JP2022170642A - Analog signal input device for disconnection detection, and control system - Google Patents

Abstract

To provide an analog signal input device for disconnection detection capable of detecting disconnection of a sensor connected to an analog signal input device.SOLUTION: In the analog signal input device, analog signals are differential input from a set of input terminals to which a sensor is connected via a first input line, and the analog signals are received by the first input part in which a first resistor is interposed between the first input lines and the same. The analog signal input device converts the analog signals which are read through a second input part having the same configuration as the first input part into a form of a multiple-bit digital signal and outputs the same. Upon receiving a prescribed instruction, a current is supplied to the power line from one of the pair of first input lines, and when the output of the second input part is greater than or equal to a predetermined threshold when the output of the first input part rises, it is determined as disconnection.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an analog signal input device that detects disconnection and a control system using the same.

An input device for detecting the state of the controlled object is connected to a control device such as a data logger that records the state of the controlled object and a PLC that controls the controlled object in a predetermined sequence. The input device is connected to a sensor for detecting the state of the controlled object, amplifies the signal from the sensor, shapes the signal, and finally converts it to a digital signal. Some sensors simply detect electrical signals such as voltage and current values, thermocouples and thermistors that detect temperature, flowmeters that detect flow rate, strain gauges that detect weight and strain, and the amount of magnetic flux. There are known devices that detect various state quantities, such as magnetic sensors such as Hall elements, antenna probes that detect radio wave intensity, frequency, etc., and convert them into electric signals and output them.

Analog signals from various sensors are converted into multi-bit digital signals that can be easily handled by a control device by an analog-to-digital converter (hereinafter also referred to as ADC) provided in the input device. If the connection between the sensor and the input device becomes disconnected due to some problem (also called an open wire), the control device cannot accurately grasp the state of the controlled object, so it is necessary to detect the occurrence of an open wire. There is For this reason, conventionally, various disconnection detection methods have been proposed. For example, Japanese Unexamined Patent Application Publication No. 2002-100002 discloses a configuration in which a minute current is passed from the detection device side to a sensor to detect disconnection of a wire between the detection device and the sensor. Also, as shown in Non-Patent Document 1, an ADC has been proposed in which the ADC itself has a function for detecting disconnection. In such an ADC, a constant current source is prepared, and when the voltage between the input terminals to which the sensor is connected becomes indistinguishable from the voltage at the time of open wire, the current from the constant current source flows between the input terminals, Disconnection detection processing is performed to detect the presence or absence of disconnection based on the behavior of the voltage rise in . Generally, the output impedance of a sensor is low and the input impedance of the input device to which the sensor is connected is high. makes a difference. This difference is discriminated to detect disconnection between the sensor and the input device.

JP 2012-8014 A

Analog-to-digital converter AD7124-4 data sheet manufactured by Analog Devices, Inc.

However, such a disconnection detection method has problems that the accuracy of measurement using a sensor is lowered for disconnection detection, and that the sensor output cannot be read when performing disconnection detection. For example, in the technique disclosed in Patent Document 1, since a minute current is passed through the sensor, the detection accuracy is affected by fluctuations in this current value. In the technique of Non-Patent Document 1, since a constant current source is connected between the input terminals while disconnection is being detected, the voltage between the input terminals rises regardless of whether a disconnection has occurred or not. However, the sensor output value cannot be read until disconnection detection is completed. Furthermore, since the supply current of the constant current source provided in the ADC of Non-Patent Document 1 is about 0.5 to 4 μA, the voltage between the input terminals rises to a value that enables determination of whether or not there is a disconnection. is long, and the period during which the output of the sensor cannot be measured may extend to several seconds. In production facilities, it is often unacceptable to have a situation in which the output of a sensor cannot be read in seconds.

The present disclosure can be implemented as the following forms or application examples.

(1) A first aspect of the present disclosure is an aspect as an analog signal input device. This analog signal input device includes a set of input terminals to which a sensor is connected, and a first input section that receives analog signals from the input terminals as differential inputs via a set of first input lines, A first input section in which a first resistor is interposed between the first input lines, and a second input section that receives analog signals from the input terminals as differential inputs via a set of second input lines. a second input section having a second resistor interposed between the second input lines, and reading the analog signal individually through the first input section and the second input section to obtain the analog a signal output unit that converts a signal into a multi-bit digital signal and outputs the signal; and a current that operates in response to a predetermined instruction and supplies current from one of the pair of first input lines to the power supply line. and determining whether or not the output of the second input section when the output of the first input section is increased by receiving the current supply from the current supply section is equal to or greater than a predetermined threshold. , and a determination unit that outputs a determination result.

The principle of disconnection detection by this analog signal input device is that when a current supply unit supplies a current from one of the first input lines of the differential input to the power supply line (for example, the ground line) in response to a predetermined instruction, this current flows through a first resistor interposed between the first input lines, the output of the first input rises, as a result of which the second input is connected at the input terminal to the first input line of the first input. A different voltage appears on the second input line of the unit depending on whether or not the connection between the input terminal and the sensor is disconnected. A first resistor is interposed between the first input lines, and the voltage between the first input lines rises due to the supply from the current supply unit. This voltage causes a current to flow in the second input line, and the voltage generated by this current across the second input line varies depending on whether or not the internal resistance of the sensor is connected to the input terminal.

In this way, in the analog signal input device that converts an analog signal into a digital signal and outputs it, a disconnection can be easily detected by using a configuration including a first input section and a second input section that receive analog signals as differential inputs. can be done. By having two input sections for receiving analog signals as differential inputs, the redundancy of the configuration for inputting analog signals is increased, and disconnection detection is performed using this redundancy, eliminating waste in the circuit configuration. can do.

(2) A second aspect of the present disclosure includes an analog signal input device that inputs an analog signal from a sensor, converts it to a digital signal and outputs it, and a control device that is connected to the analog signal input device and controls the system. , is a configuration as a control system. In this control system, the analog signal input device includes a set of input terminals to which the sensors are connected, and a first input that receives analog signals from the input terminals as differential inputs via a set of first input lines. a first input unit having a first resistor interposed between the first input lines; and receiving analog signals from the input terminals as differential inputs via a pair of second input lines. a second input section in which a second resistor is interposed between the second input lines; and the analog signal separately through the first input section and the second input section a signal output unit that reads and converts the analog signal into a form of a multi-bit digital signal and outputs the signal to the control device; a current supply unit that supplies a current from one of the input lines to a power supply line; and an output of the second input unit when the output of the first input unit is increased by receiving the current supply from the current supply unit. is equal to or greater than a predetermined threshold value, and a determination result notification unit that outputs the determination result to the control device, and the control device receives the analog signal input device from the One of the conditions is that the magnitude of the digital signal corresponding to the detected value of the received sensor is indistinguishable from the case where the sensor is not connected to the input terminal of the analog signal input device. an instruction output unit that outputs the predetermined instruction to the analog signal input device; and a control signal output unit for outputting a control signal to the outside in the case of an abnormal state in which it cannot be determined that the state is not normal.

In this control system, it is possible to easily detect disconnection in the analog signal input device, which is one of the devices constituting the control system, in a highly redundant configuration. Therefore, waste in terms of circuit configuration can be eliminated. In addition, the analog signal input device that constitutes the control system and the control device that controls the system can cooperate to detect disconnection, and the reliability of the control system can be enhanced.

1 is a schematic configuration diagram showing a control system including an analog signal input device according to a first embodiment; FIG. FIG. 2 is a circuit diagram showing a specific configuration of an input section; FIG. 4 is an explanatory diagram showing the format of a communication packet for exchanging data between devices; FIG. 4 is an explanatory diagram showing an example of packets exchanged between devices; 4 is a flowchart showing a flow rate measurement processing routine; FIG. 4 is an explanatory diagram showing a route through which current flows when disconnection is detected; 4 is a timing chart showing how disconnection is detected; 4 is a flowchart showing an input signal confirmation processing routine; FIG. 2 is a schematic configuration diagram showing a control system including an analog signal input device according to a second embodiment; 8 is a flowchart showing a flow rate measurement processing routine of the second embodiment; 9 is a flow chart showing a flow rate measurement processing routine of the third embodiment; FIG. 11 is a flowchart showing the details of third voltage acquisition determination processing added in the third embodiment; FIG. FIG. 11 is a timing chart showing how disconnection detection is performed in the third embodiment; FIG.

A. First embodiment:
(A1) Hardware configuration:
FIG. 1 shows the configuration of a control system 20 including the analog signal input device 40 of the first embodiment. The control system 20 includes a control device 30 that controls the processing of the entire system, an analog signal input device 40 that receives analog signal input, and an output device 80 that drives actuators and the like, all of which are connected via a communication line 90 . In FIG. 1, only one analog signal input device 40 and one output device 80 are shown for one control device 30, but in reality, a plurality of input devices including an input device for receiving digital signal input are shown. An input device and multiple output devices may be included in control system 20 . The control device 30 is also called a PLC (Programmable Logic Controller).

In the first embodiment, the flow meter 11 is connected to the analog signal input device 40 as an example of the sensor. In this example, an analog signal input device 40 is used to receive an analog signal from a flowmeter 11 that measures the flow rate of the fluid flowing through the pipe 13 in the system, and the flow rate of the fluid inside the pipe 13 is measured. The analog signal input device 40 outputs a signal corresponding to the measured flow rate to the control device 30 via the communication line 90 . The control device 30 calculates the control amount of the flow control valve 17 according to the flow rate, outputs this to the output device 80 , and controls the actuator 15 with the output device 80 .

The flow meter 11 and the input terminal 50 of the analog signal input device 40 are connected by a twisted pair cable 19 that is less susceptible to noise. This is the same for the connection of the actuator 15 as well. Of course, other types of wires such as parallel cables may be used for connection.

The control device 30 includes a known CPU 31 , memory 32 , communication section 35 and display section 37 . The control device 30 communicates with the analog signal input device 40 and the output device 80 via the communication line 90 by the communication unit 35 to control various quantities such as the flow rate of the fluid flowing through the pipe 13 .

The analog signal input device 40 has a set of input terminals 50 for connecting the flow meter 11, and a first input section 51 and a second input section 52 connected thereto. Further, the analog signal input device 40 supplies a constant current to the signal output unit 55 and the first input unit 51 that convert analog signals input from the first input unit 51 and the second input unit 52 into digital signals and output the digital signals. A current supply unit 57, a CPU 41 with a built-in memory that controls the entire analog signal input device 40, a disconnection detection determination unit 43 realized by a program executed by the CPU 41, and communication with other devices via a communication line 90. A communication unit 45 and a power supply unit 47 that supplies power to the entire analog signal input device 40 are provided. In FIG. 1 and other figures, the positive voltage line Vcc side is indicated by a horizontal bar, and the ground line GND side is indicated by a downward ▽ mark.

The CPU 41 is connected to the signal output section 55 and the communication section 45 , and can read the flow rate of the fluid in the pipe 13 measured by the flow meter 11 by reading the digital signal output by the signal output section 55 . Further, the result can be transmitted to the CPU 31 of the control device 30 via the communication unit 45, or disconnection detection can be performed in response to an instruction from the CPU 31, and the result can be notified to the CPU 31. An analog signal input device 40 receives an analog signal input to one input terminal 50 via first and second input sections 51 and 52 and analog/digital converters ADC1 and ADC2, that is, the same analog signal is input to two systems. It can be handled by hardware. The reason why such one analog signal can be handled by two systems is that the hardware is duplicated to increase its redundancy, and even if a failure occurs in one input system, the flow rate will be controlled by the other input system. This is to ensure a state in which measurement can be continued and to enhance the safety of the system. The configurations of the first input section 51, the second input section 52, and the signal output section 55 will be described in detail later. This kind of duplication is applied to all analog signals that are input, but of course the importance of analog signals in the system is graded, and in order to ensure the safety of the system, analog signals with a high rank are duplicated. It is also possible to avoid duplicating analog signals that do not or have a low degree of safety concern. In addition, triplex or higher multiplexing may be performed to increase security.

The output device 80 includes a CPU 81 that controls the entire device, a memory 82 that stores programs and data necessary for control, an output unit 85 that outputs driving signals to external devices, and a communication unit that performs communication via a communication line 90. 87. The CPU 81 executes the programmable program stored in the memory 82 to drive the actuator 15 coupled to the external device such as the flow control valve 17 via the output section 85 . Various devices such as a motor and a solenoid can be used as the actuator 15 . Also, the CPU 81 can communicate with the control device 30 via the communication unit 87 , receive instructions from the control device 30 , and transmit the current status of the output device 80 to the control device 30 .

Next, the circuit configuration of the analog signal input device 40 will be described in detail with reference to FIG. Although the analog signal input device 40 is a module capable of inputting a plurality of analog signals, only the configuration for processing one analog signal is shown in the figure. The analog signal input device 40 is provided with a plurality of input terminals. One of the input terminals 50 is connected to the twisted pair cable 19 from the flowmeter 11 shown in FIG. Inside the analog signal input device 40 , two pairs of signal lines 61 and 62 are connected to the input terminal 50 . Hereinafter, these are referred to as a first input line 61 and a second input line 62, respectively.

The first input section 51 is connected to the first input line 61 , and the second input section 52 is connected to the second input line 62 . The first input section 51 and the second input section 52 have exactly the same internal configuration in this embodiment. In the figure, boxes marked with R denote resistors, and boxes marked with C denote capacitors.

A resistor R11, a first voltage dividing resistor RD1 of the voltage dividing circuit 65, noise removing resistors R13 and R14, and an operational amplifier OP1 are connected to one of the pair of first input lines 61 from the input side. The output of OP1 is connected to the plus side input terminal I0+ of the analog-to-digital converter ADC1 via a noise removing resistor R15. A resistor R21, noise removing resistors R23 and R24, and an operational amplifier OP2 are connected to the other side of the first input line 61 from the input side.・Connected to the minus side input terminal I0- of the digital converter ADC1. The second voltage dividing resistor RD2 of the voltage dividing circuit 65 is interposed between the connection point of the first voltage dividing resistor RD1 and the resistor R13 and the other of the first input line 61. FIG. The voltage dividing circuit 65 divides the voltage input to the input terminal 50 into RD1/(RD1+RD2) by two resistors, that is, a first voltage dividing resistor RD1 and a second voltage dividing resistor RD2. Here, each symbol RD1 and RD2 is the resistance value of each resistor RD1 and RD2. The voltage dividing circuit 65 is configured using a resistor having a sufficiently high resistance value, for example, about 100 kΩ, with respect to the output impedance of the sensor, here the flow meter 11 . The voltage dividing ratio of the voltage dividing circuit 65 is not particularly limited, and may be in the range of about 1:100 to 100:1. The voltage division ratio may be determined from the voltage input to the input terminal 50 and the voltage that the signal output section 55 can accept.

As shown, a set of signal lines from the flow meter 11 input to the input terminal 50 are connected to a set of first input lines 61 of the first input section 51 . Since the voltage dividing circuit 65 described above is interposed in the first input line 61, when the voltage of the signal from the flowmeter 11 exceeds the voltage range that the first input section 51 can input, The voltage of the signal from the flow meter 11 is reduced by the voltage dividing circuit 65 to a voltage range that the first input section 51 can input. If the voltage range of the signal from the flow meter 11 is within the voltage range that can be input by the first input section 51, the voltage dividing circuit 65 is not necessary, so the first voltage dividing resistor RD1 is removed and the resistor R11 and resistor R13 are short-circuited, and the second voltage dividing resistor RD2 is connected across the first input line 61 as it is. The first input line 61 is a differential input to the first input section 51 . Therefore, the input signal from the flowmeter 11 is less susceptible to noise (differential noise) on the power supply line. The other of the first input lines 61 forming the differential input is connected to the ground line GND from the connection point between the resistors R21 and R23 via the ground resistor RG and the analog/digital converter ADC1. .

Capacitors C1 and C2 are interposed between the connection points of the noise removing resistors R13, R14 and R23, R24 and the ground line GND. A capacitor C3 is interposed on the input side of the operational amplifiers OP1 and OP2 of the noise removing resistors R14 and R15. On the analog-to-digital converter ADC1 side of the noise elimination resistors R15 and R25, capacitors C4 and C5 are interposed between the ground line GND and a capacitor C6 is interposed between the input terminals I0+ and I0-, respectively. is dressed.

Both the operational amplifiers OP1 and OP2 are configured as voltage followers for increasing the input impedance. The input terminal + of the operational amplifier OP1 is connected to the current source 57S of the current supply unit 57, and the sink 57D of the current flowing from the current source 57S is connected between the ground resistor RG and the ground line GND of the analog/digital converter ADC1. Connected to the connection point. Since the input impedance of operational amplifier OP1 is high, current from current source 57S flows through the circuit on the side of resistor R14 connected to operational amplifier OP1. The current flow from the current supply section 57 will be described later.

The second input section 52 has the same internal configuration as the first input section 51 described above, except that the current supply section 57 is not connected, so detailed description thereof will be omitted. The second input 52 is connected to the set of input terminals 50 via the set of second input lines 62, the output of the second input 52 being the positive input terminal of the analog-to-digital converter ADC2. They are connected to the I0+ and negative side input terminals I0-, respectively.

The output of the analog/digital converter ADC1 and the output of the analog/digital converter ADC2 are connected to the CPU41. In this embodiment, the analog/digital converters ADC1, ADC2 and the CPU 41 are connected by serial communication, but they may be connected in parallel with a predetermined number of bits. The signal output unit 55 connected to the first input unit 51 and the second input unit 52 converts the analog signal from the flowmeter 11 connected to the input terminal 50 into a digital signal at a predetermined interval, and the CPU 41 output to The CPU 41 reads this and outputs it to the control device 30 via the communication section 45 .

Data exchange between devices, including the case where analog signal input device 40 transmits data to control device 30 , is performed by communication via communication line 90 . An example of a bucket used for this communication is shown in FIG. Since the configuration of the packet is determined by each device, it can be configured in any way. If the communication line 90 is a so-called intranet (registered trademark) conforming to the Internet, the TCP/IP protocol is used for the transport layer and the network layer, and the application layer may be determined between devices.

FIG. 3 is an explanatory diagram showing an example of the packet PT used in this embodiment. The packet PT includes a header portion HD and a data portion DT. At the beginning of the header portion HD is the destination DS of the packet, and at the end of the header portion HD is the number and type of data contained in the packet PT. contains a plurality of bits DP indicating The number of data in the data part DT is information as to how many data DD having a predetermined number of bits are included. The data type indicates whether each data DD is text TX (8 bits), numerical value Ns (8 bits), numerical value Nw (16 bits), or floating-point numerical value Nf (32 bits).

The data part DT included in each packet PT is headed by a data number DN, followed by a 3-bit status command SC, followed by 8-bit, 16-bit, or 32-bit data. DD is placed. Since the number and types of data contained in the data portion DT differ for each packet PT, each packet PT has a variable length. The data number DN corresponds to the analog signal number handled by the analog signal input device 40 . For example, if the analog signal input device 40 can input four analog signals, the data number DN1 indicates the analog signal connected to the first input terminal 50. FIG.

FIG. 4 shows, as such a packet PT, a packet PTAC transmitted from the analog signal input device 40 to the control device 30, a packet PTCA transmitted from the control device 30 to the analog signal input device 40, and a packet PTCA transmitted from the control device 30 to the output device 80. Three types of packet PTCOs that are used are exemplified. These packets contain a 3-bit status command SC, the content of which differs depending on the packet type. This status command SC is represented as a flag F in the packet PTAC transmitted from the analog signal input device 40 to the control device 30 . When the flag F=0, the data indicates that the measurement is normally performed, and the measured value is set in the data DD. If the flag F=1, it indicates that a disconnection of the sensor has been detected, and the data DD is invalid. When the flag F=2, it indicates that a short circuit between the input terminals 50 has been detected, and the data DD is invalid in this case as well. If the flag F=3, it indicates that the measurement result exceeds the maximum value (OF), and the data is set to $FF.

In packet PTCA transmitted from control device 30 to analog signal input device 40, status command SC is represented as flag G. FIG. In this packet PTCA, data DD is basically invalid. A flag G=0 indicates an instruction to continue the measurement to the analog signal input device 40 . Flag G=1 is an instruction to detect disconnection to analog signal input device 40 . Flag G=2 is an instruction to detect a short-circuit to analog signal input device 40 . Flag G=3 is an instruction to stop the analog signal input device 40 .

In the packet PTCO transmitted from the control device 30 to the output device 80, the status command SC is represented as a flag H. In this packet PTCO, when the flag H=0, it indicates an instruction to control the actuator 15 to the target value, and the data DD is the target value. When the flag H=1, it indicates an instruction to control the actuator 15 to the minimum value, and the data DD is the minimum value to be controlled. When the flag H=2, it indicates an instruction to control the actuator 15 to the maximum value, and the data DD is the maximum value to be controlled. When the flag H=3, it indicates that the output to the actuator 15 is turned off immediately, and the data DD is $00.

(A2) Flow rate measurement process:
Based on the above-described circuit configuration and method of communication between devices, flow rate measurement processing performed by the analog signal input device 40 together with the control device 30 will be described. FIG. 5 is a flowchart showing a flow rate measurement processing routine executed by the analog signal input device 40. As shown in FIG.

First, flow rate measurement processing performed by the analog signal input device 40 will be described. The processing shown in FIG. 5 is repeatedly executed at predetermined intervals at which packets can be received via the communication line 90 . When the process is started, the packet is first read from the communication line 90, and when it is determined that the packet is addressed to the analog signal input device 40 from the controller 30 by looking at the destination of the packet, the packet is read. (step S100). The contents of the packet received by the analog signal input device 40 of the present embodiment from the control device 30 are as shown as packet PTCA in FIG.

Therefore, the analog signal input device 40 checks each data in order from the first data number DN1 included in the data portion DT of the received packet PTCA, and particularly checks the flag G, which is the status command SC (step S110). . As already described, this flag G indicates that the control device 30 has instructed execution of disconnection detection when the flag G has a value of 1 . Therefore, if the flag G is not 1, disconnection detection is not performed, and the analog signal input device 40 digitizes the voltage signal from the flow meter 11 input via the first input section 51 by the analog/digital converter ADC1. It is converted into a signal and read (step S120). Furthermore, following this, the analog signal input device 40 converts the voltage signal from the flow meter 11 input via the second input unit 52 into a digital signal by the analog/digital converter ADC2 and reads it (step S122). . In the present embodiment, since the input system for converting one analog signal into a digital signal and reading it is duplicated, the signal from the same flow meter 11 is read by two systems. A voltage read from the first input section 51 through the analog-to-digital converter ADC1 is called a first voltage V1, and a voltage read from the second input section 52 through the analog-to-digital converter ADC2 is called a second voltage V2. call. The CPU 41 reads the first voltage V1 and the second voltage V2 individually (steps S120 and S122), and then sets the flag F as a status command SC when transmitting the first voltage V1 and the second voltage V2. 0 is set (step S155).

On the other hand, if the value of the flag G is 1 in the judgment of step S110 (step S110: "YES"), the process of step S125 and subsequent steps is performed assuming that the disconnection detection process is to be performed. The processing in which the control device 30 instructs the analog signal input device 40 to detect disconnection using the flag G will be described in detail later, but the analog signal input device 40 detects the instruction to detect disconnection. The output of the flow meter 11 is output in a state indistinguishable from the voltage when disconnection occurs. Therefore, the voltage of the signal input to the first input terminal 50 is approximately zero when the disconnection detection is started. In this state, when analog signal input device 40 starts disconnection detection processing in step S125 and subsequent steps, it first operates current supply unit 57 to perform processing for supplying a constant current from current source 57S to sink 57D (step S125). . A route RT1 through which current flows at this time is shown in FIG. Current flows from current source 57S through resistors R14, R13, second voltage divider resistor RD2, and ground resistor RG into sink 57D. The sink 57D is connected to the ground line GND of the entire device.

Since the current supply unit 57 can supply a current of several mA or more, the first voltage V1 across the second voltage dividing resistor RD2 is Due to the constant current Ic that rises in a short time and is supplied by the current supply unit 57,
Vop=RD2·Ic
becomes. This state is shown in FIG. In the figure, the case where there is no disconnection and the case where there is disconnection and the flowmeter 11 is not connected to the first input terminal 50 (open wire) are drawn side by side. Via, the detection result of the analog-to-digital converter ADC1 quickly becomes the voltage Vop when the disconnection detection period is started. Therefore, the first voltage V1 through the first input section 51 is read (timing t1 shown in FIG. 7). It is determined that it is time to read the voltage (step S131: "YES"), and the voltage on the side of the second input section 52 in this state is converted at timing t2 shown in FIG. (step S132). This voltage corresponds to the above-described second voltage V2 if disconnection detection is not performed. , it does not rise like the first voltage V1. Therefore, this is called a second minute voltage V2d.

The second minute voltage V2d is generated by the following circuit configuration. As shown in FIG. 6, when disconnection detection is performed and a constant current is supplied from the current supply unit 57, a current flows through a route RT1, and Vop is applied across the second voltage dividing resistor RD2. voltage is generated. Since the second input line 62 of the second input section 52 is connected in parallel to the first input line 61 of the first input section 51, the second input line 62 of the second input section 52 has a second branch line. The voltage across piezoresistor RD2 will be added. In this case, the current will flow along the route RT2 shown in FIG. In FIG. 6, among the resistors of the second input section 52, the resistors involved in the route RT2 are matched with the resistors of the first input section 51, using a small letter r, resistor r11, resistor r21 , a first voltage dividing resistor rd1, and a second voltage dividing resistor rd2. Using these symbols, route RT2 is specifically: first voltage dividing resistor RD1→resistor R11→resistor r11→first voltage dividing resistor rd1→second voltage dividing resistor rd2 →resistor r21→resistor R21.

If the flowmeter 11 is correctly connected to the first input terminal 50 and there is no disconnection in the connection of the flowmeter 11, the internal resistance of the flowmeter 11 will be between the lines of the second input line 62. RS is connected. Since the internal resistance RS of the flowmeter 11 is relatively small, the current flowing through the route RT2 is extremely small. Since the current flowing through the route RT2 is smaller than the constant current flowing through the route RT1, the second minute voltage V2d detected via the second input section 52 has a value of approximately 0 when there is no disconnection. . Of course, if the flowmeter 11 is outputting a significant signal indicating the flow rate during disconnection detection, the second minute voltage V2d will be a voltage corresponding to this signal. This case is shown in the left column of FIG.

On the other hand, if the connection between the flowmeter 11 and the first input terminal 50 is lost for some reason and a disconnection occurs, the first voltage dividing resistor RD1 to the resistor R21 are connected to the second voltage dividing resistor. Since a circuit connected in parallel with the resistor RD2 is not formed, the amount of current flowing through the second voltage dividing resistor rd2 increases compared to when there is no disconnection, and the amount of current flowing through the second voltage dividing resistor rd2 increases accordingly. The second minute voltage V2d detected via the unit 52 rises. This state is illustrated in the right column of FIG.

Therefore, it is determined whether or not the second minute voltage V2d read in step S132 is greater than the threshold value Vref (step S140). ), and if not exceeded, the process moves to step S155, and the value 0 is set to the flag F. When the resistance value of the route RT1 from the current source 57S to the sink 57D is about 130 kΩ, and when disconnection occurs in the connection between the flowmeter 11 and the input terminal 50, the measured value of the second minute voltage V2d is 25 mV. was beyond Therefore, in this embodiment, a value of approximately 20 mV is set as the threshold value Vref.

After performing the above processing, a communication packet is prepared (step S160). Specifically, the data number DN for sending the data of the input signal connected to the input terminal 50, the value of the flag F as the status command SC, the first voltage V1 and the second voltage V2 as the data DD to be sent are prepared in the format of the packet PTAC shown in FIG. When the determination in step S140 is "NO" and the packet for communication is prepared through the process of step S155 (step S160), the first voltage V1 and the second voltage V2 are set to zero. After that, this packet PTAC is transmitted via the communication unit 45 (step S170), and the above-described flow rate measurement processing routine ends. In this packet PTAC, as shown in FIG. 4, when the flag F has a value of 1 or 2, the data is invalid. .

The packets thus transmitted are transmitted via the communication line 90 and received by each device connected to the communication line 90 . The control device 30 constantly acquires packets from the communication line 90, and when the acquired packet is a packet PTCA addressed to the control device 30 from the analog signal input device 40, executes the input signal confirmation processing routine shown in FIG. do. When this process is started, first, the process of reading the contents of the packet PTAC from the analog signal input device 40 is performed (step S200). Next, the value of the flag F of the status command SC included in this packet PTAC is discriminated (step S210).

When the flag F has a value of 0, that is, when the measurement using the flow meter 11 in the analog signal input device 40 is normally performed, the first voltage V1 and the second voltage V2 included in the packet PTAC are read out, It is determined whether the two match (step S220). If the flag F has a value of 1 in step S210, a disconnection is detected, and if the first voltage V1 and the second voltage V2 do not match in step S220, the first input unit 51 or It can be determined that some abnormality has occurred in the second input unit 52 . Note that V1=V2 is a judgment including a predetermined allowable range. When it is determined that some kind of abnormality has occurred, the fact that an abnormality has been detected is displayed on the display section 37 (step S225). Then, assuming that the output device 80 is instructed, the flag H is set to 1 (step S230), a packet PTCO for the output device 80 is formed, and this packet PTCO is output to the output device 80. FIG.

As shown in FIG. 4, in the packet PTCO, the flag H of the status command SC being 1 indicates a command to control the actuator 15 to the minimum value. Also, the data DD of this packet indicates the minimum value in that case. Although no particular flow chart is shown for processing, the output device 80 receiving this packet PTCO controls the actuator 15 at the fastest speed to the minimum value indicated by the data DD since the flag H=1. Controlling the actuator 15 to the minimum value means to set the flow rate to the minimum, for example zero, in this embodiment. Such control is performed for the purpose of controlling the system on the safe side.

For example, if the fluid flowing through the pipe 13 is a fluid that promotes a reaction, the flow rate of the fluid is minimized to suppress the acceleration of the reaction and ensure the safety of the system. Conversely, if the object is being cooled, for example, by a fluid or coolant, the actuator 15 may be controlled to the maximum value at the fastest speed to prevent overheating and ensure system safety. When the flag H has a value of 0, normal control is performed to control the actuator 15 up to the target value. The minimum value control when H=1 and the maximum value control when H=2 are similar to normal control in that the actuator 15 is controlled to the minimum or maximum value. , other actuators, etc., are not controlled in a time-sharing manner, but the designated actuator is controlled to the minimum or maximum value at the fastest speed. In this way, when it is determined that some kind of abnormality has occurred, after setting the flag H and outputting the packet PTCO, the flag of the status command SC is included in the packet PTCA output to the analog signal input device 40. G is set to a value of 3 (step S240).

On the other hand, if the determination in step S220 is "YES", that is, if the first voltage V1 and the second voltage V2 match, it can be determined that the measurement by the analog signal input device 40 was performed properly. It is determined whether or not the first voltage V1 is equal to or lower than a preset threshold value V0 (step S250). This threshold value V0 is set to a low voltage that makes it difficult to distinguish from disconnection, which is actually several tens of millivolts. If it is determined that the first voltage V1 is equal to or less than the threshold value V0, it is determined whether this determination is the first determination of the day (step S260), and if it is the first determination of the day, an instruction to detect disconnection is issued. As a preparation, the value 1 is set to the flag G (step S270). The value of this flag G is a flag referred to in the flow rate measurement processing routine ( FIG. 5 , step S110) in the analog signal input device 40 already described. Since disconnection does not occur frequently, it suffices to check once a day when the control system 20 is in operation. Of course, the disconnection detection instruction may be issued every time the first voltage V1 becomes equal to or lower than the threshold value V0, or the disconnection detection instruction may be issued once every several times.

If the first voltage V1 is not equal to or lower than the threshold value V0 (step S250: "NO"), or if the determination is made for the second time or later on the current day (step S260: "NO"), the flag G is set to a value of 0. (Step S280). After setting flag G (steps S240, S270, S280) as described above, packet PTCA for analog signal input device 40 is prepared and transmitted to analog signal input device 40 (step S285). With this, the input signal confirmation processing routine ends.

According to the analog signal input device 40 of the first embodiment described above, and the control system 20 including the device 40, the control device 30, and the output device 80, analog signal input capable of converting an analog signal into a digital signal and outputting it In the device 40, disconnection of the connection of the flowmeter 11 to the input terminal 50 can be easily detected. By having two input sections 51 and 52 for receiving analog signals as differential inputs, the redundancy of the configuration for inputting analog signals is increased, and disconnection detection is performed using this redundancy. Waste can be eliminated.

Moreover, since the current supply unit 57 used for disconnection detection supplies a sufficient amount of current to the circuit resistance, the time required for disconnection detection can be shortened. Since the analog-to-digital converters ADC1 and ADC2 are provided for each of the two input sections 51 and 52, the voltages of the two input sections 51 and 52 can be measured almost simultaneously. can be completed at home. Moreover, when there is no disconnection, the second minute voltage V2d measured by the second input section 52 is the same as the second voltage V2 normally detected by the second input section 52, so the disconnection is being detected. However, the magnitude of the analog signal from the flow meter 11 can be measured. These features are particularly desirable when control system 20 is an industrial PCL device. When the control system 20 controls the production line, there is no delay in grasping the state of the object, and the state of the sensor can always be grasped, so the quality of the product can be sufficiently ensured, and the delay in the input of the analog signal can be reduced. There is no possibility that defective products will be produced due to

Furthermore, in the present embodiment, the control device 30 issues a wire breakage detection instruction to the analog signal input device 40, and the frequency and timing of wire breakage detection performed by the analog signal input device 40 is determined by the operation status of the control system 20 as a whole. can be properly determined by looking at In the present embodiment, the voltage of the analog signal from the flow meter 11 detected by the first input unit 51 becomes equal to or less than the threshold value V0 (several tens of mV) within a day when the control system 20 is in operation. Since the disconnection is detected only at the timing, the subsequent flow rate measurement can be performed after confirming the occurrence of the disconnection. Moreover, if the analog signal from the flow meter 11 does not have a value that can be taken when disconnection occurs, the disconnection detection itself is not performed, so that disconnection detection does not waste time.

Furthermore, in this control system 20, when disconnection is detected, the output device 80 is used to drive the actuator 15 that controls the physical quantity being measured by the sensor (here, the flow meter 11) in which the disconnection has occurred. , control is performed on the side that enhances the safety of the system to be controlled. Therefore, a decrease in system safety can be suppressed.

B. Second embodiment:
Next, an analog signal input device 40A of a second embodiment and a control system using this device will be described. FIG. 9 is a schematic configuration diagram of an analog signal input device 40A of the second embodiment. The overall control system has the same configuration as the first embodiment shown in FIG. The analog signal input device 40A of the second embodiment has substantially the same configuration as the analog signal input device 40 of the first embodiment, but each of the first input section 51 and the second input section 52 is provided with an analog/digital converter. It differs from the first embodiment in that a single analog-to-digital converter ADC is connected via a multiplexer (MPX) 71 instead of having ADC1 and ADC2. The multiplexer 71 switches between the output of the first input section 51 and the output of the second input section 52 according to an instruction from the CPU 41 or at predetermined intervals. The output of the multiplexer 71 is input to an analog-to-digital converter ADC via an amplifier (AMP) 73 , converted into a multi-bit digital signal, and read into the CPU 41 . The analog/digital converter ADC has the same function as the analog/digital converters ADC1 and ADC2 of the first embodiment. Also, the amplifier 73 is a gain variable amplifier, and its amplification degree is switched by a signal from the outside. In this embodiment, the gain is switched by the CPU 41 .

The CPU 41 of the analog signal input device 40A having the above configuration executes the flow rate measurement processing routine shown in FIG. This processing routine is basically the same as the processing routine of the first embodiment shown in FIG. 5, and differs therefrom in the following two points. One is that processing for switching the multiplexer 71 is provided between steps S120 and S122. Another is that step S131 in the first embodiment consists of step S131a for performing switching processing of the multiplexer 71, step S131b for setting the gain of the amplifier 73, and step S131c for determining the passage of time T1. The difference is that it is replaced with the readable judgment processing 131A.

As described above, in the second embodiment, a single analog-to-digital converter ADC is provided for the first input section 51 and the second input section 52, and the process of reading the first voltage V1 (step After S120), the multiplexer 71 is switched to switch the input of the analog/digital converter ADC from the output of the first input section 51 to the output of the second input section 52 (step S121). After the switching process by the multiplexer 71 (step S121), the second voltage V2 is obtained (step S122).

In the readable judgment processing 131A, after the signal from the first input section 51, that is, the first voltage V1 is acquired when disconnection is detected, the multiplexer 71 is operated to prepare for the acquisition of the second minute voltage V2d. The signal from the 2-input unit 52 is switched (step S131a), and the gain is set to increase the gain of the amplifier 73 (step S131b). Since the voltage detected by the second input unit 52 when detecting disconnection is a low voltage of about several tens of mV, increasing the gain facilitates the detection of the voltage and improves the detection accuracy. After that, in the second embodiment, after the time T1 has passed (step S131c), the process of acquiring the second minute voltage V2d (step S132) is performed. In the second embodiment, since the multiplexer 71 is switched, it is not confirmed whether the first voltage V1 has become sufficiently high. Since the time required for the first voltage V1 to become sufficiently high when the constant current is supplied by the current supply unit 57 can be obtained in advance, this time T1 is set. It acquires the voltage V2d.

According to the second embodiment described above, the same effects as those of the first embodiment can be obtained. can be simplified. Further, since the second minute voltage V2d is read by increasing the gain of the amplifier 73, there is an effect that the accuracy of disconnection detection can be improved.

C. Third embodiment:
Next, a third embodiment will be described. In the third embodiment, the same hardware configuration as that of the control system 20 including the analog signal input device 40 of the first embodiment is used, and the processing routine shown in FIG. , the flow rate measurement processing routine shown in FIG. 11 is executed. This processing routine is basically the same as the processing routine of the first embodiment shown in FIG. 5, but differs in the following two points. One is the provision of an initial voltage Vi acquisition determination process (step S115) that branches to step S120 or S125 after step S110. The point is that it has a judgment process (step S145). The processing of the third embodiment will be described below, focusing on these steps S115 and S145.

As in the first embodiment, first, the value of the flag G is determined (step S110), and when it is determined that the flag G has a value of 0, that is, an instruction to detect disconnection has been received, the initial voltage Vi acquisition determination is performed in the third embodiment. The process (step S115) is executed. In this process, first, the voltage between the first input terminals 50 is acquired as the initial voltage Vi using the first input unit 51 (step S115a). Subsequently, it is determined whether the initial voltage Vi is substantially equal to 0 volt (step S115b). The term "substantially equal" as used herein means within ±10% of the value being compared. Of course, the range may be set in advance, and may be, for example, a range of ±5%. Although the initial voltage Vi is acquired using the first input section 51 here, it may be acquired using the second input section 52 .

It is often the case that the flag G is set to 1 and disconnection detection is performed at a timing when the flow meter 11 is not yet operating, such as when the system is started. Therefore, normally there will be no output from the flow meter 11 and the initial voltage Vi should be approximately equal to 0 volts. On the other hand, if the initial voltage Vi deviates from 0 volts and the voltages cannot be said to be substantially equal (step S115b, "NO"), the flowmeter 11 is considered to be operating, so disconnection detection is not performed. Instead, the process proceeds to step S120 to perform a process of obtaining the first voltage V1 and the second voltage V2, a process of setting the flag F to a value of 0, and the like. Since these processes have already been described in the first embodiment, description thereof will be omitted.

On the other hand, when it is determined that the initial voltage Vi is approximately equal to 0 volt (step S115b, "YES"), the current supply unit 57 is operated to supply a constant current as described in the first embodiment. Specifically, a process (step S125) is performed to flow a constant current from the current source 57S to the sink 57D, acquire the first voltage V1 and the second minute voltage V2d (steps S130 to S132), and obtain the second minute voltage V2d. It is determined whether the voltage V2d is greater than the threshold Vref (step S140).

Then, in the third embodiment, the process of step S145 is executed. As shown in FIG. 12, this step S145 includes a process of stopping the supply of the constant current and waiting for a certain period of time (step S145a), and a process of acquiring the third voltage V3d using the second input unit 52 ( Step S145b) and a process of determining whether the third voltage V3d is substantially the same as the first voltage V1 (Step S145c). In step S145a, the current supply unit 57 is made to stop supplying the constant current, and the process waits for a predetermined period of time. Waiting for the passage of the predetermined time is because the circuit has capacitive components such as stray capacitance and capacitor C3, and even if the supply of the constant current is stopped, the current flowing through the second voltage dividing resistor rd2 will not immediately flow. This is because the third voltage V3d can take a significant value without becoming 0 volts.

The timing of constant current supply by the current supply unit 57 is shown in the upper part of FIG. As already explained, when the flag G is determined to be 1, the process of obtaining the initial voltage Vi is immediately performed. This timing is shown in the figure as t0. If the initial voltage Vi is approximately equal to 0 volts (step S115b, "YES"), following this determination, the supply of constant current is started at timing Tion. This is the timing corresponding to the processing in step S125 of FIG. When the supply of constant current is started, the voltage across the second voltage dividing resistor RD2 increases with the current flowing from the current source 57S to the sink 57D. This change in voltage is shown as a solid line J1 in the middle of FIG. This change is the same as the first voltage shown in FIG. 7 in the first embodiment. At the timing t1 after the timing Tion at which the supply of the constant current is started, the first voltage V1 is acquired by the first input unit 51 (step S130). This voltage Vop is, as described in detail in the first embodiment,
Vop=RD2·Ic
becomes.

On the other hand, the detected voltage of the second input section 52 when a constant current is supplied exhibits different behavior depending on the presence or absence of disconnection. The difference in voltage caused by the presence or absence of disconnection is shown in comparison with FIG. After a predetermined time has passed since the acquisition of the first voltage V1 and timing t2 at which the second minute voltage V2d can be read, the second input section 52 operates the second divided voltage of the second input section 52. A voltage across the resistor rd2 is obtained as a second minute voltage V2d (step S132).

After that, the supply of the constant current is stopped at timing Tioff, waiting for a certain period of time (step S145a), and at timing t3, the second input unit 52 acquires the third voltage V3d (step S145b). Since the constant current supply from the current supply unit 57 is stopped, the measured third voltage V3d is normally the voltage before the constant current supply, that is, approximately 0. This state is shown as a solid line J2 in FIG. On the other hand, if there is no disconnection in the wiring from the flowmeter 11 to the first input terminal 50 and the signal from the flowmeter 11 is input by chance at the timing of disconnection detection, the second input unit 52 detects The voltage signal is shown as dashed line B2. In the figure, circles indicate to which of solid lines J1, J2, and dashed line B2 the voltage obtained at predetermined timings t0 to t3 corresponds.

When the third voltage V3d is obtained in this way (FIG. 12, step S145b), it is determined whether or not the third voltage V3d is substantially the same as the initial voltage Vi (step S145c). If both are substantially equal (step S145c, "YES"), it is determined that a disconnection has occurred, and the process proceeds to step S150 (FIG. 11). At step S150, a value 1 is set to a flag F indicating whether or not disconnection is detected, and a packet is prepared and transmitted (steps S160 and S170). On the other hand, if it cannot be determined that the two are substantially the same (FIG. 12, step S145c, "NO"), the reason why the second minute voltage V2d exceeded the threshold Vref (step S140, "YES") is not due to disconnection. Instead, it is determined that the signal sent from the flowmeter 11 was a voltage higher than the threshold value Vref (second minute voltage V2d), and the value 0 is set to the flag F (FIG. 11, step S155) to prepare the packet. is transmitted (steps S160, S170). Note that when the determination in step S145c is "NO" and the packet for communication is prepared through the process of step S155 (step S160), the voltage obtained in step S130 is used as the first voltage V1, The voltage (third voltage V3d) obtained in step S145b is set as the voltage V2.

The case where the third voltage V3d could not be determined to be substantially the same as the initial voltage Vi will be described with reference to FIG. Immediately after Tioff, the voltage detected by the second input section 52 decreases. This is because, if the constant current supplied by the current supply unit 57 is lost in the disconnection state, no potential difference occurs across the second voltage dividing resistor rd2. This is because V3d is about the initial voltage Vi (approximately 0 volts) obtained by the first input unit 51 at timing t0. On the other hand, if the third voltage V3d acquired by the second input section 52 at the timing t3 is not at the same level as the initial voltage Vi, even if the third voltage V3d is lower than the threshold Vref, the disconnection cannot occur. , the signal from the flow meter 11 is detected.

According to the third embodiment described above, when the current supply unit 57 starts supplying a constant current in response to a disconnection detection instruction (G=1), the flow meter 11 sets the threshold Vref at the time of disconnection detection. When a voltage signal that exceeds the voltage is input, it is not erroneously detected as disconnection. In this embodiment, the initial voltage Vi and the third voltage V3d are obtained before the supply of the constant current (timing t0) and after the supply is stopped (timing t3). This is because it is possible to determine for which reason the second minute voltage V2d acquired at the time (timing t2) was generated. If it is determined that V3d≈Vi at timing t3, it is possible to detect whether or not the wiring from the flow meter 11 to the first input terminal 50 is broken. That is, in the third embodiment, when a signal is input from the flowmeter 11, it is not erroneously detected that a disconnection has occurred. Other effects are the same as those of the first embodiment.

Although the hardware configuration similar to that of the first embodiment is assumed in the third embodiment, similar processing can be performed using a hardware configuration similar to that of the second embodiment. For convenience of understanding, at timing t2 in FIG. 13, the voltage detected by the second input unit 52 when disconnection occurs and the signal from the flowmeter 11 when disconnection does not occur are input. In this case, the voltage detected by the second input unit 52 has the same height, but the signal from the flowmeter 11 does not necessarily match the second minute voltage V2d generated by supplying the constant current. It does not matter if the two are different.

In each of the above-described embodiments, the flag F has a binary value of 1 (disconnection has occurred) or 0 (it cannot be determined that a disconnection has occurred), but in step S115b If the determination is "NO" or if the determination in step S145c is "NO", the flag F may be set to a value other than 0 or 1. Alternatively, the obtained voltages Vi, V1, V2, V2d, and V3d may be sent as data to the control device 30, and the control device 30 may determine whether or not there is a disconnection.

In some of the above-described embodiments, after the flag G has a value of 1 and the disconnection detection process is started, the conditions for disconnection detection are met, for example, when the determination in step S140 is "NO". If not, the flag F is set to 0 (step S155), and the process proceeds to packet preparation (step S160). If it is determined that the disconnection detection conditions are not met, steps S120 and S122 are executed to measure the first voltage V1 and the second voltage V2, as in the case where the flag G is not 1, and then You may make it perform the process after step S155. Alternatively, the flag F is set to a value other than 0 or 1, that is, a value indicating that disconnection detection was attempted but conditions for disconnection detection were not met, and a packet that does not include voltage-related data is prepared. It may be assumed that

D. Other aspects:
(1) Such an analog signal input device 40 can also be implemented with the following configuration. For example, the analog signal input device includes a set of input terminals to which a sensor is connected, and a first input section that receives analog signals from the input terminals as differential inputs via a set of first input lines, A first input section in which a first resistor is interposed between the first input lines, and a second input section that receives analog signals from the input terminals as differential inputs via a pair of second input lines, , a second input with a second resistor interposed between the second input lines, and the analog signal is separately read through the first and second inputs to convert the analog signal into a multi-bit digital a signal output unit that converts the signal into a signal form and outputs a signal; a current supply unit that operates in response to a predetermined instruction and supplies a current to the power supply line from one of the pair of first input lines; a determination unit that determines whether or not the output of the second input unit when the output of the first input unit is increased is greater than or equal to a predetermined threshold and outputs the determination result. may be In this way, in an analog signal input device capable of converting an analog signal into a digital signal and outputting it, a disconnection can be easily detected using a configuration including a first input section and a second input section that receive analog signals as differential inputs. can be done. By having two input sections for receiving analog signals as differential inputs, the redundancy of the configuration for inputting analog signals is increased, and disconnection detection is performed using this redundancy, eliminating waste in the circuit configuration. can do.

The principle of disconnection detection is that the output of the first input unit rises due to the current supplied from one of the first input lines of the differential input from the current supply unit to the power supply line (for example, the ground line), but the output of the first input unit rises. Different voltages appear in the second input line of the second input section connected to the first input line of the one input section depending on whether or not the connection between the input terminal and the sensor is disconnected. A resistor or capacitor is normally interposed between the first input lines for noise elimination or voltage division, and the voltage between the first input lines rises due to the supply from the current supply section. This voltage causes a current to flow in the second input line, and the voltage generated across the second input line by this current differs depending on whether the internal resistance of the sensor is connected to the input terminal. The current supplied from the current supply unit is desirably a constant current in order to be able to manage the magnitude of the voltage rise, but it does not have to be a constant current. Moreover, if the magnitude of the current is sufficiently large with respect to the circuit resistance of the first input section, the time required for disconnection detection can be shortened, which is preferable. Being able to shorten the time required for disconnection detection is particularly desirable in industrial applications. In a production line or the like, if the status of an object is not grasped for a significant amount of time, or if it cannot be grasped for a significant amount of time, the quality of the product cannot be sufficiently ensured, and defective products may be produced. Such a situation can be avoided if rapid disconnection detection becomes possible. Of course, under the condition that disconnection detection can take time, for example, if disconnection detection is performed during initialization processing at startup, the current value can be sufficiently increased with respect to the circuit resistance of the first input section. It is also possible to detect disconnection with a small current without using a current. The predetermined instruction for the current supply unit to start supplying current may be given from the outside as an instruction for the disconnection detection operation, or may be a simple instruction given at predetermined intervals. Also, such an instruction may be given as an instruction to start a series of diagnostic operations for ascertaining that the analog signal input device is operating normally. In this case, disconnection detection may be performed as one of a series of operation checks.

Sensors to detect disconnection may be sensors that simply detect electrical signals such as voltage and current values, thermocouples and thermistors that detect temperature, flowmeters that detect flow rate, and sensors that detect weight and strain. It may be a sensor that detects various state quantities, such as a strain gauge that detects, a magnetic sensor such as a Hall element that detects the amount of magnetic flux, and an antenna probe that detects radio wave intensity, frequency, and the like. The sensor may be of any kind as long as it can detect some physical quantity and is connected to the input terminal of the analog signal input device by wire.

The sensor and the analog signal input device need only be connected by wire at least at the connection point with the analog signal input device side, and there is no problem even if a part of the sensor side is wirelessly connected. As for the wired connection, it is preferable to use a cable with high noise resistance such as a twisted pair cable. If the noise resistance performance is not a problem, a general parallel cable may be used for connection. A shielded cable may also be used to improve noise immunity.

(2) In such a configuration, the first resistor and the second resistor are provided as resistors constituting a voltage dividing circuit that adjusts the magnitude of the voltage of the analog signal from the sensor. may be By doing so, the resistor of the voltage dividing circuit can be used as a resistor that causes a voltage rise due to the current from the current supply unit, and the circuit configuration can be simplified. Of course, apart from the resistors of the voltage dividing circuit, or instead of the resistors of the voltage dividing circuit, a resistor is provided for causing a voltage rise between the first input lines of the first input part due to the current from the current supply part. may

(3) In such a configuration, a capacitor having a capacitance larger than the parasitic capacitance of the first input line may be interposed between the first input line and the power supply line. This makes it possible to eliminate noise on the first input line, which is a differential input. When such a capacitor is provided, part of the current supplied from the current supply section is used to charge the capacitor, so that the rise in the voltage between the first lines is delayed accordingly. Therefore, when such a capacitor is provided, the amount of current to be supplied by the current supply section should be determined in consideration of the capacitance of the capacitor and the delay in voltage rise time.

(4) In such a configuration, the threshold is set at the second input when the sensor is not connected to the input terminal by the voltage generated across the first resistor by the current supplied from the current supply. It may be determined corresponding to the voltage generated across the second resistor due to the current flowing into the line. By doing so, it is possible to detect the presence or absence of disconnection simply by comparing the voltage generated in the second resistor with the threshold value.

(5) In such a configuration, a communication unit that exchanges a signal including the digital signal with a control device is provided, and the communication unit is configured such that the magnitude of the digital signal included in the exchanged signal is determined by the sensor. and the input terminal is within a range that can occur when the connection between the input terminal and the input terminal is broken. It may be performed for the supply section. In this way, disconnection detection can be performed under the instruction of the control device when there is a possibility of disconnection, and unnecessary disconnection detection is not performed. Even if the magnitude of the digital signal included in the exchanged signal is within the range that can occur when the connection between the sensor and the input terminal is disconnected, it is not necessary to detect the disconnection each time. Not necessarily. The disconnection detection may be performed only once every several times. In that case, the determination may be made by the control device, or may be made by the analog signal input device which receives an instruction from the control device. Even if the condition is satisfied, the disconnection detection may be performed once a day, for example, when the condition is satisfied for the first time, instead of performing the disconnection detection every time.

(6) In such a configuration, the determination unit transmits the determination result to at least one of a management device that manages a control system to which the analog signal input device is connected, and a presentation device that presents the determination result to a user. It may be output to one side. If the determination result is output to the management device, it can be used for management of the control system by the management device. On the other hand, if the judgment result is presented to the user by the presentation device, the user can easily take appropriate measures upon receiving the presentation of the judgment result indicating the presence or absence of disconnection. Of course, you can do both. The management device may be a control device that controls a controlled object in the control system, or may be a device dedicated to management, such as a diagnosis computer. How to use the determination result regarding the presence or absence of disconnection may be determined in the system design. The presentation of the determination result by the presentation device may be displayed on a display or the like, or may be reported by voice. Of course, only the fact that a wire breakage has occurred may be presented, or information such as which sensor of which device was broken and when the wire was broken may be presented together. The presence or absence of disconnection may simply be recorded.

(7) In such a configuration, the signal output section includes a first analog/digital converter that converts the analog signal received via the first input section into the digital signal, and the a second analog-to-digital converter for converting an analog signal to said digital signal. In this way, the analog signal input to the first input section and the analog signal input to the second input section can be independently output as digital signals, and the two signals can be output substantially simultaneously. Therefore, digital signals can be output in a short period of time in spite of being multiplexed.

(8) In such a configuration, the signal output section includes an analog/digital converter that selectively converts the analog signal received via the first input section and the second input section into a digital signal by time division. It may be prepared. This can reduce the number of analog/digital converters and simplify the configuration. In order to selectively convert to a digital signal by time division, a multiplexer may be provided to switch between the output of the first input section and the output of the second input section. Of course, a single switch, such as a relay, SSR, analog switch, etc., may be individually provided and turned on/off exclusively. If the output stages of the first input section and the second input section are provided with a configuration capable of making the output high impedance, such as a tri-state buffer, the outputs may be wired-coupled. In this case, the output stage on the data measuring side of the first input section and the second input section is switched from the high impedance state to the normal output state during measurement.

(9) In such a configuration, in the first case where the determination unit determines that the output of the second input unit receiving the current supply from the current supply unit is equal to or greater than a predetermined threshold, the A second controller that outputs the determination result that the connection to the sensor is disconnected and determines that the output of the second input unit that receives the current supply from the current supply unit is less than a predetermined threshold value. In this case, the determination result that the connection to the sensor is disconnected may not be output. In this way, the analog signal input device outputs the result of determining whether or not there is a disconnection, so that the external device can easily take necessary measures in response to this determination result.

(10) In such a configuration, in the first case, the determination unit determines the output of the second input unit after stopping the current supply, and determines the output of the second input unit after stopping the current supply. When the output drops to the level before receiving the current supply, outputting the judgment result that the connection to the sensor is broken, and outputting the second input section after stopping the current supply. does not drop to the level before receiving the current supply, the determination result that the connection to the sensor is broken may not be output. In this way, the analog signal input device outputs the determination result of determining whether or not there is a disconnection, so that the external device can easily take necessary measures in response to this determination result, and the disconnection detection process can be performed. It becomes easy to avoid erroneously detecting disconnection when an output exceeding the threshold value is received from the sensor to the second input section when performing this operation.

(11) As an aspect other than the above, implementation as a control system is also possible. The control system includes an analog signal input device for inputting an analog signal from a sensor, converting it to a digital signal and outputting it, and a control device connected to the analog signal input device for controlling the system. In this control system, the analog signal input device includes a set of input terminals to which the sensors are connected, and a first input that receives analog signals from the input terminals as differential inputs via a set of first input lines. a first input unit having a first resistor interposed between the first input lines; and receiving analog signals from the input terminals as differential inputs via a pair of second input lines. a second input section in which a second resistor is interposed between the second input lines; and the analog signal separately through the first input section and the second input section a signal output unit that reads and converts the analog signal into a form of a multi-bit digital signal and outputs the signal to the control device; a current supply unit that supplies a current from one of the input lines to a power supply line; and an output of the second input unit when the output of the first input unit is increased by receiving the current supply from the current supply unit. is equal to or greater than a predetermined threshold value, and a determination result notification unit that outputs the determination result to the control device, and the control device receives the analog signal input device from the One of the conditions is that the magnitude of the digital signal corresponding to the detected value of the received sensor is indistinguishable from the case where the sensor is not connected to the input terminal of the analog signal input device. an instruction output unit that outputs the predetermined instruction to the analog signal input device; and a control signal output unit for outputting a control signal to the outside in the case of an abnormal state in which it cannot be determined that the state is not normal. In this way, as a control system, disconnection detection in the analog signal input device can be easily performed in a highly redundant configuration. Therefore, waste in terms of circuit configuration can be eliminated. In addition, the analog signal input device that constitutes the control system and the control device that controls the system can cooperate to detect disconnection, and the reliability of the control system can be enhanced. In the analog signal input device that constitutes this control system, disconnection detection is performed by combining two input sections for inputting analog signals, and the current supplied by the current supply section can be increased. If it can be shortened and there is no disconnection, the analog signal can be read even during the disconnection detection operation. If the control system is an industrial PCL device, it is particularly desirable to be able to shorten or eliminate the disconnection detection time. In a production line controlled by an industrial PLC, if the status of an object is not grasped for a significant amount of time or is delayed, the quality of the product cannot be sufficiently ensured, and defective products may occur. . Such a situation can be avoided if rapid disconnection detection is possible, or if analog signals can be input even during disconnection detection.

(12) Such a configuration may further include an output device connected to the control device, wherein the output device is an actuator involved in controlling a physical quantity whose behavior is detected by the sensor to which the analog signal input device is connected. may be connected so as to be able to drive the actuator, and when the control signal is received from the control device, the behavior of the physical quantity drives the actuator toward a state where the safety of the control system is increased. . By doing so, it is possible to enhance the safety of the system in the event that the connection with the sensor is broken.

(13) In such a configuration, in the control system, each device constituting the control system is interconnected by a communication line, and at least the control device receives the digital signal, the predetermined instruction, the judgment Results and said control signals may be exchanged with other devices by communication over said communication line. In this way, it becomes easy to make each device cooperate by communication, and by using this communication, it is possible to easily realize a predetermined instruction for disconnection detection and the sharing of the result thereof.

(14) In each of the above embodiments, part of the configuration implemented by hardware may be replaced by software. At least part of the configuration implemented by software can also be implemented by a discrete circuit configuration. In addition, when part or all of the functions of the present disclosure are realized by software, the software (computer program) can be provided in a form stored in a computer-readable recording medium. "Computer-readable recording medium" means not only portable recording media such as flexible disks and CD-ROMs, but also various internal storage devices such as RAM and ROM, and fixed to computers such as hard disks. It also includes an external storage device. That is, the term "computer-readable recording medium" has a broad meaning including any recording medium capable of fixing data packets instead of being temporary.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in the respective modes described in the Summary of the Invention column may be used to solve some or all of the above problems, or Substitutions and combinations may be made as appropriate to achieve part or all. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

ADC, ADC1, ADC2 --- analog/digital converters, OP1, OP2 --- operational amplifiers, PTAC, PTCA, PTCO --- packets, RD1 --- first voltage dividing resistor, RD2 --- second voltage dividing resistor, 11 --- flow meter, 13 Piping 15 Actuator 17 Flow control valve 19 Twisted pair cable 20 Control system 30 Control device 31 CPU 32 Memory 35 Communication unit 37 Display unit 40, 40A ... analog signal input device, 41 ... CPU, 43 ... determination section, 45 ... communication section, 47 ... power supply section, 50 ... input terminal, 51 ... first input section, 52 ... second input section, 55 ... signal output section, 57 Current supply unit 57D Sink 57S Current source 61 First input line 62 Second input line 65 Voltage dividing circuit 71 Multiplexer 73 Amplifier 80 Output device 81...CPU, 82...memory, 85...output section, 87...communication section, 90...communication line

Claims (13)

An analog signal input device,
a set of input terminals to which sensors are connected;
A first input unit that receives analog signals from the input terminals as a differential input via a pair of first input lines, the first input having a first resistor interposed between the first input lines. Department and
A second input unit that receives analog signals from the input terminals as a differential input via a set of second input lines, the second input having a second resistor interposed between the second input lines. Department and
a signal output unit that individually reads the analog signals through the first input unit and the second input unit, converts the analog signals into multi-bit digital signals, and outputs the analog signals;
a current supply unit that operates in response to a predetermined instruction and supplies a current from one of the pair of first input lines to a power supply line;
determining whether or not the output of the second input section when the output of the first input section is increased by receiving the current supply from the current supply section is equal to or greater than a predetermined threshold, and displaying the determination result; a determination unit that outputs;
An analog signal input device with 2. The analog signal according to claim 1, wherein said first resistor and said second resistor are each provided as resistors forming a voltage divider circuit for adjusting the magnitude of the voltage of said analog signal from said sensor. input device. 3. The analog signal input device according to claim 1, wherein a capacitor having a capacitance equal to or larger than a stray capacitance parasitic on said first input line is interposed between said first input line and said power supply line. . The threshold is determined by the voltage generated across the first resistor due to the current supplied from the current supply and by the current flowing into the second input line when the sensor is not connected to the input terminal. 4. An analog signal input device according to any one of claims 1 to 3, defined corresponding to the voltage across the second resistor. The analog signal input device according to any one of claims 1 to 4,
A communication unit that exchanges signals including the digital signal with a control device,
The control device, wherein the communication unit determines that the magnitude of the digital signal included in the exchanged signal is within a range that can occur when the connection between the sensor and the input terminal is broken. When receiving the instruction signal output by the, performs the predetermined instruction to the current supply unit for disconnection detection,
Analog signal input device. 3. The determination unit outputs the determination result to at least one of a management device that manages a control system to which the analog signal input device is connected and a presentation device that presents the determination result to a user. The analog signal input device according to any one of claims 1 to 5. The signal output section includes a first analog-to-digital converter for converting the analog signal received via the first input section into the digital signal, and a first analog-to-digital converter for converting the analog signal received via the second input section into the digital signal. 7. An analog signal input device according to any one of claims 1 to 6, comprising a second analog-to-digital converter for converting. 3. The signal output unit comprises an analog/digital converter for selectively time-divisionally converting the analog signal received via the first input unit and the second input unit into a digital signal. Item 7. The analog signal input device according to any one of items 6. The analog signal input device according to any one of claims 1 to 8,
The determination unit
In a first case where it is determined that the output of the second input section receiving the current supply from the current supply section is equal to or greater than a predetermined threshold value, the determination is made that the connection to the sensor is broken. output the result,
In a second case where it is determined that the output of the second input section receiving the current supply from the current supply section is less than a predetermined threshold, it is determined that the connection to the sensor is broken. do not output judgment results,
Analog signal input device. The determination unit
In the first case, determining the output of the second input section after stopping the current supply,
outputting the determination result that the connection to the sensor is disconnected when the output of the second input unit drops to the level before receiving the current supply after the current supply is stopped;
If the output of the second input unit does not decrease to the level before receiving the current supply after the current supply is stopped, the determination result that the connection to the sensor is broken is not output.
10. The analog signal input device according to claim 9. A control system comprising an analog signal input device for inputting an analog signal from a sensor, converting it to a digital signal and outputting it, and a control device connected to the analog signal input device for controlling the system,
Analog signal input device
a set of input terminals to which the sensors are connected;
A first input unit that receives analog signals from the input terminals as a differential input via a pair of first input lines, the first input having a first resistor interposed between the first input lines. Department and
A second input unit that receives analog signals from the input terminals as a differential input via a set of second input lines, the second input having a second resistor interposed between the second input lines. Department and
a signal output unit that individually reads the analog signals through the first input unit and the second input unit, converts the analog signals into multi-bit digital signals, and outputs the analog signals to the control device; ,
a current supply unit that operates in response to a predetermined instruction from the control device and supplies a current from one of the pair of first input lines to a power supply line;
a determination unit configured to determine whether or not the output of the second input unit when the output of the first input unit is increased in response to the current supply from the current supply unit is equal to or greater than a predetermined threshold;
a determination result notification unit that outputs the result of the determination to the control device;
with
The control device is
The magnitude of the digital signal corresponding to the detected value of the sensor received from the analog signal input device is indistinguishable from the case where the sensor is not connected to the input terminal of the analog signal input device. As one of the conditions, an instruction output unit that outputs the predetermined instruction to the analog signal input device;
When the judgment result received from the analog signal input device is an abnormal state in which it cannot be judged that the connection between the sensor and the input terminal of the analog signal input device is not disconnected, a control signal is output to the outside. a control signal output unit for output;
comprising
control system. 12. A control system according to claim 11, wherein
Further comprising an output device connected to the control device,
The output device is
is connected so as to be able to drive an actuator involved in control of a physical quantity whose behavior is detected by the sensor to which the analog signal input device is connected;
When the control signal is received from the control device, the actuator is driven toward a state in which the behavior of the physical quantity increases the safety of the control system.
control system. In the control system, each device constituting the control system is interconnected by a communication line,
13. The control according to claim 11, wherein at least said control device exchanges said digital signal, said predetermined instruction, said judgment result and said control signal with another device by communication via said communication line. system.

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