JPS63168571A - 2-wire type transmitter - Google Patents

Abstract

PURPOSE:To achieve calculation in a wide measuring range accurately, by arranging a polarity discriminator for voltage to be supplied and a range switch for switching conversion characteristic according to the polarity of the voltage. CONSTITUTION:This 2-wire type transmitter SC has two ranges to set an input/ output conversion characteristic thereof SC corresponding to the two ranges by switching while sending out a signal converted. The polarity of a supply power source to the transmitter SC on the side of a receiver RC is set by switching with a polarity setter 10. Consequently, the transmitter SC discriminates the polarity of the supply power source while outputting a range switching signal corresponding to the positive or negative of the polarity from polarity discriminator 4. The switch 20 changes the input/output conversion characteristic over to that corresponding to the range switching signal from the device 4. Thus, two ranges are automatically switched by this two-wire method, thereby enabling accurate calculation in a wide measuring range.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a two-wire transmission system having dual range input/output conversion characteristics, and more specifically, to a two-wire transmission system with an improved range switching mechanism. Concerning vessels.

<Conventional technology> Conventionally, in order to accurately measure physical quantities over a wide measurement range,
There is a transmitter that divides the measurement range into multiple ranges, converts it into an electrical signal, and transmits the signal to a receiver. In such a multi-range transmitter, in addition to two transmission lines that supply power to the transmitter and transmit the transmitter's DC 4 to 20 mA output signal, there is also a discrimination signal line that transmits a signal for determining the range. was necessary. Therefore, with a two-wire transmitter that connects the transmitter and receiver with only two transmission lines, only one range can be measured and transmitted.

To solve this problem, an AC signal of a specific frequency is superimposed on the output signal of 4 to 20 mA DC, and the frequency of the AC signal is used to determine which range the output signal corresponds to, thereby measuring multiple ranges. A two-wire transmitter configured as described above has been proposed (an example of such a two-wire transmitter is Japanese Utility Model Application Publication No. 175764/1983).

<Problems to be Solved by the Invention> However, such a conventional two-wire transmitter requires a plurality of AC oscillators or a frequency-switchable AC oscillator on the transmitter side. There was a problem that the circuit became complicated.

Furthermore, since the AC excavator consumes a large amount of power, it has been difficult to apply this configuration to a transmitter such as a two-wire electromagnetic flowmeter, which has large power consumption constraints.

Furthermore, the receiver side requires a filter that separates the DC 4 to 20 mA output signal from the AC signal for range determination, and a circuit that detects the frequency of the AC signal.
If the frequency of the range discrimination signal is set high, the attenuation of the discrimination signal will increase as the transmission distance increases, making it difficult to receive.On the other hand, if the frequency is set low, the filter shape will become larger and the output signal and range discrimination There was a problem in that it was difficult to separate the signal from the signal.

<Purpose of the Invention> The present invention was made in order to solve the above problems, and it is possible to configure the circuit simply, suppress the increase in power consumption, and accurately determine the range. The purpose of the present invention is to provide a dual range two-wire transmitter.

<Means for Solving the Problems> The present invention has a function of converting an input physical quantity into an electrical signal and outputting it, and the power consumed for the conversion is reduced by two wires used for transmitting the output electrical signal. A two-wire transmitter supplied through the transmission line is provided with two input/output conversion characteristics, a means for determining the polarity of the supplied voltage, and a range switching means for switching the conversion characteristics according to the polarity of the voltage. This makes it possible to perform dual range measurements, making it possible to measure a wide range and perform forward and reverse measurements.

Effect> In the present invention, the polarity determining means of the two-wire transmitter determines the polarity of the supplied power and outputs a range switching signal corresponding to positive and reverse polarities.

The range switching means switches the human output conversion characteristic to the input/output conversion characteristic of the range corresponding to the range switching signal from the polarity determining means.

Therefore, the input/output conversion characteristics of the two-wire transmitter are switched in accordance with the polarity of the supplied power, and transmission is performed by outputting dual range output signals.

<Example> An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a two-wire transmitter according to an embodiment of the present invention, in which SC is a transmitter, RC is a receiver, and Ll
, L2 are two transmission lines connecting the transmitter SC and the receiver RC.

The transmitter SC has a detector 1 that converts a physical quantity, such as a flow rate, into an electrical signal, and the electrical signal is amplified by an amplifier AI, converted to a digital quantity by an A/D converter 2, and inputted to a microprocessor 3. Ru.

The microprocessor 3 reads the digital amount from the A/D converter 2 at a predetermined timing based on a predetermined program, and receives a range switching signal E3 from the polarity determining means 4, which will be described later, and controls the range switching means, etc. It mainly consists of a CPU that executes processing, a ROM that stores fixed information such as program data, and a RAM that temporarily stores data related to arithmetic processing by the CPU in a readable and writable manner. After the digital quantity input to the microprocessor 3 is subjected to arithmetic processing corresponding to a predetermined range, a voltage signal E1 is sent to the D/A converter 5.
is converted to

The voltage signal E1 is applied to the differential amplifier A2 and the transistor Tr2.
and is input to a voltage-current conversion circuit made up of resistors R1 to R5. Then, the differential amplifier A2 controls the transistor Tr2 so that the voltage signal E1 and the voltage E2 generated across the current detection resistor R5 provided on the negative line have a proportional relationship, and the voltage signal E1 increases. Then, E
The value of voltage E2 is increased until l and E2 are proportionally balanced. Therefore, two transmission lines L1. The current flowing through L2 is increased or decreased in proportion to El.

In the embodiment, the polarity determining means 4 includes a transistor Trl, a diode D1, and resistors R6 and R7, and the base of the transistor Tri is connected to 21 points connected to the transmission line L1 via a diode DI and a resistor R6. Ori,
The collector is connected to the output positive line of the constant voltage circuit A3 via a resistor R7. When the transmission line L1 has positive polarity, the transistor Tri is turned on, and the collector output, that is, the range switching signal E3, is at a low level. When the transmission line L1 is negative polarity, the transistor Tr1 is turned off, and the range is switched. Signal E3 becomes high level. still,
The diode D1 becomes reverse biased when the 21st point becomes negative polarity, and prevents the reverse leakage current between the emitter and base of the transistor Tri from flowing by bypassing the current detection resistor R5. Therefore, the output of the transmitter sc No errors occur in the signal.

The diode bridge D2 is a bridge rectifier for full-wave rectification, and regardless of whether the polarity of the power supplied from the transmission lines LL and L2 is positive or reverse, the output terminal positive side P2 of the diode bridge D2 always has the positive polarity. It is formed to be.

A receiver RC most suitable for combination with the above-mentioned transmitter SC has the following configuration. That is, the receiver RC includes a power source ES for the transmitter SC, and the power source ES is connected to the switch SW.
, two transmission lines Ll through a load resistance RL for current detection.
, L2 so that a voltage is supplied to the transmitter sc&:. The receiver RC is provided with a switch SW for switching the polarity of the supplied power between positive and reverse, and a setting device 6 for driving the switch SW.
The setting device 6, which constitutes the polarity setting means 10, amplifies the voltage signal obtained by converting the output signal (4 to 20 mA DC) of the transmitter SC with the load resistor RL with the amplifier 7 and outputs the output voltage VO, The output voltage VO is the comparator CMI,
Input to CM2. The comparators CMI and CM2 are set to reference voltages ECI and EC2, respectively, and the outputs of the comparators CMI and CM2 are input to the determination circuit 8.
In response to this, the determination circuit 8 outputs a setting signal to switch the switch SW to the A side or the B side.
1, EC2 has an input/output conversion characteristic, for example, as shown in FIG. (that is, the maximum output signal), and when the output signal for switching from the second range to the second range is 02, the reference voltage ECI is set to a voltage equivalent to C1, and the reference voltage EC2 is set to a voltage equivalent to C2. Then, while the switch SW is on the A side and the measurement of the lunge is being performed, when the flow rate on the QA edge line decreases below Q2, the output voltage vO becomes the reference voltage EC2, and the comparator CM2 becomes H level. . Upon receiving this, the judgment circuit 8
The switch SW is switched to the B side, the polarity of the transmission line L1 is set to negative, and the transmitter SC is switched to measurement in the second range. Also, when the switch SW is on the B side and the second range measurement is being performed, if the flow rate on the QB line increases to 02 or more, the output voltage VO becomes greater than the reference voltage ECI, and the comparator CMI becomes L level. Become. In response to this, the determination circuit 8 switches the switch SW to the A side, and the transmission line L1
With the polarity set as positive, the transmitter SC switches to the measurement of the first lunge.

Note that the output voltage 0 is outputted to an indicator, an integrating type, etc. via a range conversion circuit (not shown) controlled by the determination circuit 8. This range conversion circuit converts the output voltage 0 corresponding to the range being measured, and outputs the output voltage vO of the first range and second range as a continuous quantity.

Next, the operation of the two-wire transmitter configured as described above will be explained.

First, when the switch SW of the receiver RC is on the A side, the polarity of the transmission line L1 becomes positive, and the power supply voltage is supplied to the transmission WSC. Therefore, a positive voltage is applied to the 21 points of the transmitter SC, the transistor Tr1 is turned on, and the range switching signal E3 of the polarity determining means 4 becomes low level.

The detected flow rate is output in the detector 1 as an electrical signal, and further converted into a digital quantity by the A/D converter 2.

Then, the microprocessor 3 starts after going through an initial set operation according to the control program as shown in the flowchart of FIG.
Read the digital quantity from k unit 2. Next, the process proceeds to step 110, and it is determined whether or not the range switching signal E3 is at a low level. If the determination is YES, the process proceeds to step 120, where the digital quantity is arithmetic processed using a coefficient corresponding to the first lunge. Next, the process proceeds to step 140 and the calculated digital amount is output to the D/A converter 5.

On the other hand, when the switch SW of the receiver RC is switched to the B side, the polarity of the transmission line L1 becomes negative, and a negative voltage is applied to the 21st point. Then, the transistor Tri is turned off, and the range switching signal E3 of the polarity determining means 4 becomes high level.

When the range switching signal E3 becomes high level, the determination in the switch 110 in the microprocessor 3 becomes No, and the process proceeds to step 130, where the digital amount is arithmetic processed using a coefficient corresponding to the second range. Then step 14
0 and outputs the calculated digital amount to the D/A converter 5. When the process of step 140 is completed, step 100
Go back and repeat the above process.

The input/output of the above microprocessor 3 is 50 tons in the second lunge and 20 tons in the human output conversion characteristics shown in Figure 3 if the full scales of the second range are selected as 50 tons and 20 tons, respectively.
At 0M3/H, the output signal is full scale 20mA, and in the second range, at 20M3/H, the output signal is full scale 20mA. Therefore, step 120
When the digital quantity calculated by the microprocessor 3 in the first lunge is a value equivalent to 50M3/H, in step 140 D
/The digital amount output to the A converter 5 is an output signal of 20 m.
This is a value equivalent to A. Further, when the digital amount calculated in the second range in step 130 is a value equivalent to 20 M3 /H, the digital amount output to the D/A converter 5 in step 140 is a value equivalent to 20 mA. In addition, step 1 above
The processing of 10°120.130 corresponds to the range switching means 20 of the present invention.

The digital quantity input to the D/A converter 5 is the voltage signal E
After being converted to 1, DC4~ from transistor Tr2
It is output as a 20 mA output signal to the receiver RC via transmission lines Ll and L2.

In the receiver RC, the output signal of the transmitter sc is converted into a voltage signal by the load resistor RL, and is input to the setting device 6.

The setting device 6 outputs a setting signal when the switch SW is on the A side and the flow rate decreases to Q2 or less (output signal is 02 or less) while measuring the lunge, switches the switch SW to the B side, and connects the transmission line. Switch the polarity of L1 to negative. Also switch sw
is on the B side and during measurement in the second range, when the flow rate increases to 92 or higher (output signal is higher than C1), a setting signal is output, the switch SW is switched to the A side, and the polarity of the transmission line L1 is set to positive. Switch. As a result, in the transmitter SC, the range is switched and measurement is performed as described above.

In addition, in Fig. 3, the flow rate is at full scale Q2 in the second range.
We showed an example of switching to the 2nd lunge when it reaches Q2.
The range may be changed at an arbitrary ratio of, for example, 90% to 20 mA of the output signal, or at an arbitrary ratio of, for example, 90% to 20 mA of the output signal. It is also possible to add hysteresis to range switching.

In addition, when a forward flow and reverse flow detector is provided to measure the flow rate of forward flow and reverse flow, it is possible to use this invention to measure the forward flow in the first lunge and the reverse flow in the second range. . Figure 4 shows an example of switching between forward flow and reverse flow.
This is a case where the full scale of the second range is set to 50M3/H and the reverse flow Q2 is set to -50M3/H. In FIG. 4, when the output signal becomes 4 mA or less during measurement with the lunge, the setting device 6 switches the switch SW to the B side, and the transmitter SC becomes the second range for backflow measurement.

For backflow measurement, the A/D converter 2 may use a known method that is compatible with both forward and reverse directions.

Furthermore, Fig. 5 is an example in which the measurement states of Figs. 3 and 4 are combined, where the full scale of the second range is set to Ql of the forward flow, for example +50M3/H, and the full scale of the second range is set to the Ql of the reverse flow.
2, for example -20M3/) (for example, -20M3/).

The physical quantity detected by the transmitter SC is temperature.

Various process variables such as differential pressure and flow rate may be used.

<Operations and Effects of the Invention> As explained above, the two-wire transmitter of the present invention has two ranges, and the human output conversion characteristics of the transmitter can be switched and set to correspond to the two ranges. A two-wire transmitter that transmits a converted signal, and the transmitter determines the polarity of the power supply by a polarity setting means that switches and sets the polarity of the power supply to the transmitter on the receiver side. At the same time, a polarity determining means outputs range switching No. 1a corresponding to positive or reverse polarity, and a range switching means switches the input/output conversion characteristic to the human output conversion characteristic of the range corresponding to the range switching signal from the polarity determining means. Because of the built-in configuration, it is possible to automatically switch between two ranges using a two-wire system, making it possible to accurately measure a wide measurement range. This makes it possible to combine a dual range with a 2-wire transmitter, maximizing its functionality as a 2-wire transmitter.

In addition, when the polarity setting means for automatic dual ranging is provided on the receiver side in this way, only the polarity determination means and range switching means are provided on the transmitter side, so the transmitter can be simplified and Can be configured at low cost. Moreover, the increase in power consumption due to the functions added to the transmitter is extremely small, making it ideal for application to transmitters with large power consumption constraints, such as two-wire electromagnetic flowmeters.

Furthermore, unlike conventional two-wire transmitters, there is no attenuation of the range discrimination signal due to long transmission distances or difficulty in separating the output signal from the discrimination signal, making it possible to accurately discriminate the range of the output signal. I can do it.

In addition, by setting the second range and the second range to the same setting, the same output signal can be obtained regardless of the connection polarity of the transmission line.Therefore, there is no need to consider polarity when connecting the transmission line, and installation work is required. It has the effect of being able to do it easily and quickly.

In addition, when the two-wire transmitter of the present invention is combined with a conventional receiver and power supply device without a polarity switching function, the two-wire transmitter of the present invention has a polarity discrimination means and two input/output conversion characteristics. The human output conversion characteristics can be changed by changing the wiring of the transmission line or by inserting a reversing switch into the transmission line. Therefore, if the timing of range switching is known in advance, the transmitter will be effective even if it is buried underground or installed in a place that cannot be easily approached by people.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of a two-wire transmitter according to an embodiment of the present invention, Fig. 2 is a flowchart showing the arithmetic processing of the range switching means of the microprocessor, and Fig. 3 is a dual range input/output conversion diagram. A diagram illustrating the characteristics, Figure 4 is a diagram showing an example of applying human output conversion characteristics to forward flow and reverse flow, and Figure 5 is a diagram showing an example of applying the input/output conversion characteristics to forward flow, reverse flow, and dual range. FIG. 4... Polarity determination means, 6... Setting device, 10... Polarity setting means, 20... Range switching means, SW... Switch, SC... Transmitter, RC... Receiver . Patent application agent: Aichi Tokei Denki Co., Ltd.

Claims (1)

[Claims] Two-wire transmission that has the function of converting an input physical quantity into an electrical signal and outputting it, and the power consumed for conversion is supplied through two transmission lines used for transmitting the electrical signal. A two-wire transmitter comprising: two input/output conversion characteristics, means for determining the polarity of the supplied voltage, and range switching means for switching the conversion characteristics according to the polarity of the voltage.