JPH075993A - Analog signal input device - Google Patents

Abstract

PURPOSE:To correct an inputted data signal to a correct value by storing a reference voltage in a reference temperature state as an expectation voltage and correcting a temperature through the use of a relation between the expectation voltage and the actual A/D-converted reference voltage. CONSTITUTION:An expectation voltage memory for storing a reference voltage outputted from an A/D converter 7 as an expectation voltage Vs at the reference temperature is formed inside a microprocessor 16. The fluctuation rate of a reference voltage V actually outputted from the A/D converter 7 to the expectation voltage becomes (fluctuation rate)=(Vs-V)/Vs. The respective data signals (a) are assumed to vary at the same rate as the reference voltage V relating to temperature fluctuation and the corrected. That is, when a data signal value after A/D conversion is defined as Da, data signal vaule Db after temperature correction becomes Db=Da+[Da(Vs-V)/Vs]. The microprocessor 16 sends out the temperature corrected data signals (a) to a host device 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention collects various analog data signals indicating the operating state of each device from plant equipment in a factory or the like, converts them into digital signals, and outputs them to a higher-level device such as a process control device. The present invention relates to an analog signal input device for sending.

[0002]

2. Description of the Related Art In a process control device for controlling the operation of plant equipment, process data (data signals) indicating the operation state from various equipments constituting a plant is collected and a predetermined process data is collected for the collected process data. The control calculation is performed to calculate the operation amount for each device and send it to each device.

Since the process control device is generally composed of a small computer, it is necessary to once convert a large number of analog data signals output from each device into digital data signals and then input them into the process control device.

An analog signal input device having such a function is constructed, for example, as shown in FIG. For example, an analog data signal a output from each sensor attached to each device of the plant is input to the analog signal input card 1 which constitutes an analog signal input device. The data signal a input into the analog signal input card 1 is applied to the first to 16th input terminals of the multiplexer 2. An analog reference voltage V is applied from the reference voltage circuit 3 obtained by dividing the control voltage Vc by the variable resistor 3a and the fixed resistor 3b to the 17th input terminal.

The multiplexer 2 is a microprocessor 4
One signal designated by the selection signal b sent from the above is selected and sent to the next amplifier 5. The amplifier 5 amplifies each of the data signals a and the reference voltage V, which are selected in order, to a predetermined signal level and sends it to the A / D converter 7 through the next isolation amplifier 6. The isolation amplifier 6 has a function of insulating the signal system power supply from the microprocessor system power supply.

The A / D converter 7 converts each input data signal a or reference voltage V into a digital data signal a or digital reference voltage V. The digital data signal a output from the A / D converter 7 or the digital reference voltage V
Is input to the microprocessor 4.

FIG. 5 is a flow chart showing the operation of the microprocessor 4. When the flow chart is started, a pointer n for selecting each input terminal of the 1st to 16th data signals a of the multiplexer 2 is initialized to 1.

Then, the selection signal b having the number designated by the pointer n is sent to the multiplexer 2. Therefore, the data signal a at the nth input terminal is selected from the multiplexer 2 and sent to the A / D converter 7 via the amplifier 5 and the isolation amplifier 5. For example, after 1 ms has elapsed from the output of the selection signal b, the A / D converter 7 is activated (P2). A / D
At the timing when the conversion process is completed, the digital data signal a output from the A / D converter 7 is read (P3).
The read data is transmitted to the host device 10 via the transmission buffer in the RAM (P4).

The pointer n is updated (n = n + 1), and when the updated pointer n is 16 or less, the process returns to P1 and the selection signal b of the corresponding pointer n is transmitted. When the updated pointer n reaches 17, the selection signal b for the reference voltage V is transmitted (P5). Then, when 1 ms has elapsed, the digital reference voltage V output from the A / D converter 7 is read (P
6). If the read reference voltage V is out of the allowable range, it is determined that the A / D converter 7 has failed, and the host device 1
A failure detection signal is sent to 0 (P7).

As described above, the microprocessor 4 executes a predetermined processing on the input digital data signal a, and then, through the interface 8 and the upper exclusive bus 9, an upper device composed of a process controller or the like. Send to 10. Further, the microprocessor 4 monitors the value of the A / D converted reference voltage V to determine whether the A / D converter 7 has a failure.

[0011]

However, the analog signal input device configured as shown in FIG. 4 still has the following problems to be solved. That is, A
When the / D converter 7 does not operate at all or outputs an abnormal value, the failure of the A / D converter 7 can be detected by the method described above.

However, a large number of electronic parts for handling analog signals such as the amplifier 5, the isolation amplifier 6 and the A / D converter 7 are incorporated in the analog signal input device. Generally, analog signals are susceptible to temperature changes.

As a result, even if the data value changes due to the temperature change in the process in which each data signal a passes through each electronic part until it is output from the A / D converter 7, the microprocessor 4 The temperature fluctuation included in the digital data signal a input from the A / D converter 7 cannot be eliminated. Therefore, the reliability of the output data signal decreases.

The present invention has been made in view of such circumstances, and stores the reference voltage in the reference temperature state of the apparatus as an expected voltage, so that the actual A / D conversion can be performed with a simple configuration. To provide an analog signal input device capable of correcting an input data signal to a correct value by using a deviation voltage of a later reference voltage from an expected voltage and significantly improving reliability of an output digital data signal. With the goal.

[0015]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an analog data signal input from the outside and a reference voltage output from a temperature-compensated reference voltage source with a multiplexer at regular intervals. In an analog signal input device for capturing an A / D conversion, outputting a data signal as a digital data signal, and monitoring an abnormal operation of an A / D conversion operation with an A / D converted reference voltage,
An expected voltage memory that stores the A / D converted reference voltage as an expected voltage when the device internal temperature is in the reference temperature state, and a deviation that calculates a deviation voltage between the actual A / D converted reference voltage and the expected voltage. The voltage calculation means and the data signal correction means for correcting the A / D converted data signal value based on the calculated deviation voltage are provided.

According to another aspect of the invention, an analog data signal input from the outside and a reference voltage output from an internal reference voltage source are taken in at a constant cycle by a multiplexer and A / D converted to obtain a data signal. Is output as a digital data signal, and A / D converted reference voltage
In an analog signal input device for monitoring an abnormal operation of a D / D conversion operation, a temperature detection unit that detects a temperature, a temperature characteristic table that stores a variation amount of an A / D converted reference voltage at each temperature, and a temperature detection unit And a data signal correction means for correcting the data signal value actually A / D converted by using the variation rate corresponding to the temperature output from the.

[0017]

In the analog signal input device thus constructed, the temperature-compensated reference voltage source that is not influenced by temperature is used, and therefore the reference voltage output from the reference voltage source is always constant. And a multiplexer and A / D
The characteristics of electronic components such as converters that handle analog signals change according to the temperature inside the device. Therefore, the reference voltage output from the A / D converter also changes according to the temperature change in the device.

A at a reference temperature state such as 25 ° C.
The reference voltage output from the / D converter is stored as the expected voltage. The deviation voltage between the reference voltage actually output from the A / D converter and the expected voltage corresponds to the deviation temperature of the in-apparatus temperature from the reference temperature. Therefore, it is possible to correct the data signal to the correct data signal value from the deviation voltage of the reference voltage by assuming that the voltage of the other data signals also fluctuates at the same rate.

According to another aspect of the invention, a temperature detecting section is provided to detect the temperature at all times when the temperature compensation type reference voltage source is not used. The rate of change of the reference voltage at each temperature is stored in the temperature characteristic table. Therefore, assuming that the A / D-converted data signal actually fluctuates at the same rate as the reference voltage, the data signal is corrected to the correct data signal value from the fluctuation rate of the reference voltage corresponding to the detected temperature. It becomes possible to do.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an analog signal input device of the embodiment. The same parts as those of the conventional analog signal input device shown in FIG. 4 are designated by the same reference numerals. Therefore, detailed description of the overlapping portions is omitted.

The analog data signal a output from each sensor 11 attached to each equipment of the plant is the signal line 1
2 is input to the analog signal input card 1 which constitutes the analog signal input device via the dedicated cable 14 which is put together by the terminal block 13 in the monitoring control room. The data signal a output from each sensor 11 has a current range of 4 to 20 mA and a voltage range of 1 to 5V.

The data signal a input into the analog signal input card 1 is applied to the first to 16th input terminals of the multiplexer 2. An analog reference voltage V is applied to the 17th input terminal from the temperature compensation type reference voltage circuit 15 in which the control voltage Vc is divided by the variable resistor 15a and the fixed resistor 15b. Therefore, the reference voltage V does not depend on the temperature t in the device.

The multiplexer 2 is the microprocessor 1
Select signal b sent from 6 through photo coupler 17
One signal designated by is selected and sent to the next amplifier 5. The amplifier 5 amplifies each of the data signals a and the reference voltage V, which are selected in order, to a predetermined signal level and sends it to the A / D converter 7 through the next isolation amplifier 6. The A / D converter 7 converts each input data signal a or reference voltage V into a digital data signal a or digital reference voltage V and sends it to the microprocessor 16.

In the microprocessor 16, for example, 2
An expected voltage memory is formed which stores the reference voltage output from the A / D converter 7 in the state of the reference temperature ts such as 5 ° C. as the expected voltage Vs.

Next, a method of correcting the temperature of each data signal a output from the A / D converter 7 will be described. Actually A /
The fluctuation rate of the reference voltage V output from the D converter 7 with respect to the expected voltage Vs is: fluctuation rate = (Vs-V) / Vs, and each data signal a has a reference voltage V with respect to a temperature change.
Assuming that it changes at the same rate as, the correction value is: correction value = data signal value after A / D conversion × variation rate. The true value of each data signal a is true value = data signal value after A / D conversion + correction value Therefore, if the data signal value after A / D conversion is Da, the correct data signal value Db after temperature correction is Db. = Da + [Da (Vs-V) / Vc]. The microprocessor 16 sends the temperature-corrected data signal a to the interface 8 and the upper dedicated bus 9
To the higher-level device 10 via the.

Next, the actual operation of the microprocessor 16 will be described with reference to the flowchart of FIG. The same parts as those in the flow chart of the conventional apparatus shown in FIG. Therefore, detailed description of the overlapping portions is omitted.

When the flow chart is started, the pointer n is initialized to 1. Selection signal b of the number designated by pointer n
To the multiplexer 2. Therefore, the nth analog data signal a is selected from the multiplexer 2 and sent to the A / D converter 7 via the amplifier 5 and the isolation amplifier 6. After 1 ms has elapsed from the output of the selection signal b,
The A / D converter 7 is activated (P2). At the timing when the A / D conversion processing is completed, the digital data signal a output from the A / D converter 7 is read (P3).

Then, the value D of the read data signal a
Temperature correction is executed for a using the correction equation described above (P3a). The fluctuation rate [(Vs-V) / Vs] is the reference voltage V output from the A / D converter 7 in the immediately preceding cycle.
The value calculated using is used. The temperature-corrected data signal a to this correct value Db is transmitted to the host device 10 via the transmission buffer in the RAM (P4).

The pointer n is updated (n = n + 1). When the updated pointer n is 16 or less, the process returns to P1 and the selection signal b of the corresponding pointer n is sent out. When the updated pointer n reaches 17, the selection signal b for the reference voltage V is transmitted (P5). Then, when 1 ms has elapsed, the digital reference voltage V output from the A / D converter 7 is read (P
6). From the reference voltage V, the variation rate [(Vs-
V) / Vs] is calculated. Then, the calculated variation rate is stored and held until the next cycle (P6a).

If the read reference voltage V is out of the allowable range, it is determined that the A / D converter 7 has failed, and a failure detection signal is sent to the host device 10 (P
7). According to the analog signal input device configured as described above, each time the reference voltage V from the reference voltage circuit 15 is selected by the selection signal b from the microprocessor 16, the fluctuation rate [(Vs-V) / Vc ] Is automatically calculated and stored until the next cycle. Therefore, the latest variation rate corresponding to the current in-apparatus temperature t is stored and held.

Then, each data signal a read in the next cycle is corrected to a digital data signal having a correct value Db by using the latest fluctuation rate. Therefore, even if the temperature t in the apparatus changes, the digital data signal s output from the analog signal input apparatus becomes a data signal that correctly corresponds to the data signal a output from the sensor 11, and the reliability of the entire apparatus is improved. Greatly improved.

Further, according to this method, since the temperature correction is performed by the software method without adding any hardware component such as an electronic component, the manufacturing cost of the entire apparatus is significantly increased. There is no.

FIG. 3 is a block diagram showing a schematic structure of an analog signal input device according to another embodiment of the present invention. The same parts as those in the embodiment of FIG. 1 are designated by the same reference numerals. Therefore, detailed description of the overlapping portions will be omitted.

In the analog signal input device of this embodiment, the reference voltage circuit for outputting the reference voltage V is shown in FIG.
As in the conventional device shown in FIG. 3, a normal reference voltage circuit 3 that is not temperature-compensated is used.

Further, a temperature detector 19 is provided adjacent to the analog signal input card 1. This temperature detector 19
Measures the temperature inside the device and sends it to the microprocessor 18 as a digital temperature t inside the device.

A temperature characteristic table 20 is connected to the microprocessor 18. In this temperature characteristic table 20, each temperature t detected by the temperature detection unit 19 is shown.
In contrast, the variation rate of the reference voltage V is stored. Specifically, for example, when the reference voltage output from the A / D converter 7 at 25 ° C. is set as the expected voltage Vs, the fluctuation rate of the reference voltage V output at each temperature t from the expected voltage Vs [( Vs-V) / Vs] is stored.

Therefore, every time the actual value Da of each data signal a output from the A / D converter 7 is read, the variation rate [(Vs-V) / Vs] corresponding to the current temperature t is calculated as a temperature characteristic. Read from table 20. Then, the correct value Db of each data signal a is calculated by the same method as described above.

Db = Da + [Da (Vs-V) / Vc] Even with such a configuration, each data signal a sent from the analog signal input device to the host device 10 has a temperature-corrected correct value Db. Since it has the data signal a that it has, it is possible to obtain substantially the same effect as that of the embodiment shown in FIG.

[0039]

As described above, according to the analog signal input device of the present invention, the reference voltage in the device temperature is stored as the expected voltage, and the expected voltage and the actual A / D-converted voltage are stored. The temperature of the data signal is corrected using the relationship with the reference voltage. Therefore, with a simple configuration, the input data signal can be corrected to a correct value, and the reliability of the output digital data signal can be significantly improved. Further, it is possible to correct the temperature of the input data signal to a correct value by using the temperature detection unit that detects the temperature and the temperature characteristic table.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an analog signal input device according to an embodiment of the invention.

FIG. 2 is a flowchart showing the operation of the apparatus of the embodiment.

FIG. 3 is a block diagram showing a schematic configuration of an analog signal input device according to another embodiment of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a conventional analog signal input device.

FIG. 5 is a flowchart showing the operation of the conventional device.

[Explanation of symbols]

1 ... Analog signal input card, 2 ... Multiplexer,
3.15 ... Reference voltage circuit, 5 ... Amplifier, 6 ... Isolation amplifier, 7 ... A / D converter, 8 ... Interface, 10 ... Upper device, 11 ... Sensor, 13 ... Terminal block, 16, 18 ... Microprocessor, 19 ... Temperature detector, 20 ... Temperature characteristic table.

Claims (2)

[Claims] 1. An A / D device that captures an analog data signal input from the outside and a reference voltage output from a temperature-compensated reference voltage source with a multiplexer at regular intervals.
An analog signal input device for converting and outputting the data signal as a digital data signal, and monitoring an abnormal operation of an A / D conversion operation with an A / D converted reference voltage, An expected voltage memory for storing the A / D converted reference voltage as an expected voltage, a deviation voltage calculation means for calculating a deviation voltage between the A / D converted reference voltage and the expected voltage, and this calculation An analog signal input device, comprising: a data signal correction means for correcting the A / D-converted data signal value based on the generated deviation voltage. 2. An analog data signal input from the outside and a reference voltage output from an internal reference voltage source are taken in at a constant cycle by a multiplexer and A / D converted, and the data signal is converted into digital data. In the analog signal input device that outputs a signal and monitors the operation abnormality of the A / D conversion operation with the A / D converted reference voltage, the temperature detection unit for detecting the temperature and the A / D conversion at each temperature are performed. A temperature characteristic table that stores the variation rate of the reference voltage, and a data signal correction unit that corrects the data signal value that is actually A / D converted using the variation rate corresponding to the temperature output from the temperature detection unit. Equipped analog signal input device.