JPS60257630A - Communication equipment - Google Patents

Abstract

PURPOSE:To supply power only with a two-wire transmission line by controlling the 1st variable impedance element inserted in series with the transmission line and the 2nd variable impedance connected in parallel with a load based on a separate reference voltage. CONSTITUTION:A control circuit comprising resistors R1, R2 and a differential amplifier A1 controls the impedance of a transistor (TR)Q1 in the direction making a line voltage VL constant in response to a voltage V1 based on a reference voltage Vr1. A control circuit comprising resistors R4, R5 and a differential amplifier A2 controls the impedance of a TRQ2 in a direction making the value of a current Ic flowing to a resistor R3 constant in response to a voltage V2 based on a reference voltage Vr2. A terminal voltage Vs across the resistor Rs is converted into a digital signal by an analog-digital converter A/D1 and the signal is given to an arithmetic circuit OP as a setting value.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention receives a signal indicated by a current value flowing through a two-wire transmission line in an industrial process or the like, and controls equipment to be controlled such as a valve. The present invention relates to a communication device that transmits a signal indicating a control state or the like based on a change in line voltage of a transmission path.

[Prior art]

In industrial processes, etc., when remotely controlling valves, etc., a receiving device called a positioner is generally installed.
A central control device transmits a signal with a current value that varies in the range of, for example, 4 to 20 mA, and a receiving device receives the signal and performs control according to the current value.

However, in the past, a two-wire transmission path was required to transmit the current value indicating the signal, and a separate two-wire power path was required to supply the power required by the receiving device. A total of four lines are indispensable, which increases the amount of wire required for the line and the number of man-hours for laying the line, resulting in high equipment costs.

In addition, conventionally, when controlling pulp, monitoring the situation, etc.
It is necessary to provide a separate transmitting device and connect this to the central control device through a dedicated transmission path, which has the disadvantage of being uneconomical in terms of equipment investment.

[Summary of the invention]

The purpose of the present invention is to fundamentally solve these conventional drawbacks, and the unified signal such as 4 to 20 mA used in industrial measurement originally represents a numerical value in the range of 0 to 16 mA, etc. Note that it contains a bias component,
A first variable impedance element and a reception impedance element are inserted in series in a two-wire transmission line, and the impedance of the variable impedance element is controlled in a direction to keep the line voltage of the transmission line constant. A series circuit consisting of a series impedance element and a second variable impedance element is connected in parallel, and the current flowing through the series impedance element is controlled to be kept at a constant value according to the bias component, and then the second variable impedance element and the second variable impedance element are connected in parallel. A load circuit is connected in parallel, the bias component is used as a power source, and the line voltage is changed according to the transmitted signal while the current flowing through the series impedance is kept constant, thereby performing transmission. , it is an object of the present invention to provide an extremely effective communication device which is capable of supplying power through only a two-wire transmission line and is equipped with a transmitting and receiving function.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to figures showing examples.

FIG. 1 is a circuit diagram, in which a two-wire transmission line connected via line terminals tl + t, , starts from the line LIIL2, and a transistor Q+ is used as the first variable impedance element. The emitter and collector of are inserted in series, and a resistor RB is connected in series on the collector side as a receiving impedance element, while a voltage divider by a resistor a Rt + R2 is connected in parallel to these. A series circuit is connected between the emitter and the collector of a resistor R3 as a series impedance element and a transistor Q2 used as a second variable impedance element.

In parallel with transistor Q2, as a load circuit, a differential amplifier AI + A2, a voltage divider circuit with resistors R4 + R5, and a digital-to-analog converter (hereinafter referred to as DAC) are connected.
) D/A1 to D/A3, analog-to-digital converter (
An arithmetic circuit OP consisting of A/DI, A/D2, microprocessor, memory, etc. is connected, and the arithmetic circuit OP is connected to the DAC-D/A1゜D/A.
The reference voltages vrl and vr2 are sent out through the terminals 2 and 2.

Here, resistor RI+R2 and differential amplifier A,
constitutes a first control circuit, and includes a DAC/D/A.

According to the voltage V1 obtained by dividing the voltage vL by resistor R1+R2, the transistor Q
By controlling the impedance of 1, for example, the line voltage vL is controlled to be 10, regardless of the line current ILO value.
v is kept at a constant value.

Further, the resistor R4+R and the differential amplifier Az constitute a second control circuit, and based on the reference voltage vrz from the DAC-D/A2, the load circuit side voltage VO of the resistor R3 is controlled by the resistor R, , R5, the impedance of the transistor Q2 is controlled in the direction of keeping the value of the current 1c flowing through the resistor R3 constant, and the current Ia is is maintained at a constant value of 4 mA, for example.

Therefore, if the resistor RI+R2 has a high resistance value and the current 11 passing through it is negligible, then the resistor Rs
The current IS flowing through is 18=IL-Ic, and by setting Ia equal to the bias component, Ill+ is, for example, only the signal component of 0 to 16 mA)
In the competition, the food end pole snow mVq winter ΔDr.

A/D l converts it into a digital signal and gives it as a setting value to the arithmetic circuit OP, and at the same time converts the actual measured value from the drive device DR, which will be described later, to the ADC@A/D2 in the same way and sends it to the arithmetic circuit OP. When the signal is given, the same circuit OP sends out a control signal by control calculation, which is converted into an analog signal by DAC@D/A3 and given to the electro-pneumatic converter E/P, which will be described later, to control the opening degree of the valve. The opening degree of the valve is set assuming that the set value and the measured value match.

In addition, in FIG. 1, negative feedback is applied to the υ differential amplifier AI+A2 by the above operation, and ■, KiV, .
, V, , Ki vr2, the following equation holds true.

VL = Vr + (1 + dirt) (1) V c = vy2 (1 + n) (2) In this case, Vrl + Vr2 is ISI where the data from the arithmetic circuit OF is constant! 7 Since it is stabilized, vL and vc are also constant, and the following equation can be obtained.

That is, IC becomes constant.

On the other hand, line current IL is expressed by the following equation.

■5-IL-■c ・・・・・・・・・・・・・・・・
... (5) Therefore, ■L is, for example, 4 to 20
mA, by setting Ic=4mA, I S
= 0 to 16 mA, and a maximum power current of 4 mA can be stably supplied to each load circuit without interfering with the reception of the signal represented by υ and 1 s.

In addition, on the central control device side, the line current is 1! due to the constant current circuit. , and even if the input impedance on the receiving end changes, the current value will not be affected.

Regarding the above, when transmitting actual measured values etc. to the control device,
In response to the transmission signal, the reference voltage Vr1. is maintained while keeping the current IC constant. As the arithmetic circuit OP changes Vr2, it changes the data to the DAC board D/A2 in a pulsed manner, so the line voltage vL changes in a pulsed manner accordingly, and thus transmission is performed. The actual measured value etc. will be indicated by the pulse code.

In other words, to keep the current c constant, 4-1, (If the numerator of formula 31 is unchanged, then VL-Vc is vR,
The following equation is obtained from equations (1) and (2).

・・・・・・・・・・・・ aυ Here, if the relationship is as follows, The following relationship holds true from θυ and 0 equation.

Therefore, if the relationship of formula 03 is maintained, ADC-A/D
++In order to change the data to AlO2 at the same time, the electric iI
The line voltage vL can be freely raised or lowered while c remains at 4 mA, for example, and transmission can be performed by changing the voltage while receiving by the current value.

It should be noted that on the control device side, by means of comparing the line voltage with a predetermined reference voltage, extracting and decoding the change, it is possible to transmit and receive the current value at the same time.

In addition, if changes in voltage Va affect the operation of each load circuit, insert a voltage stabilization circuit to the part where electric current switch 2 connects, and connect a resistor R4 + R% circuit to the input side of this circuit. do it.

FIG. 2 is a block diagram showing the entire configuration of the communication device. The received output from the communication device CE shown in FIG. Pressure corresponding to the output is sent to the drive device DR such as a cylinder or air cylinder, which drives the valve V to control the opening degree, and is also driven by a potentiometer etc. connected to the drive shaft.
The current opening degree is detected as an actual measurement value and given to the communication device CE.

Therefore, power is supplied only through the 21/M type transmission line, and monitoring information is also transmitted through the communication device CE, which greatly reduces the amount of wire required and the number of man-hours required for installation. Moreover, since a separate transmitter is not required, equipment costs can be reduced.

However, in FIG. 1, other controllable variable impedance elements such as field effect transistors and photocouplers may be used in place of transistors Q+ and Q2, and an impedance element such as a diode may be used in place of resistor R8+R3. The same applies if you use DAC-D/A+, D
/ Regardless of A2, the reference voltage V is determined by a constant voltage diode, etc.
rl l VF6 may be generated and these may be switched at the time of transmission, and the arithmetic circuit OP may be configured by a combination of various logic circuits, or may be configured by an analog circuit! ll
Configure DAC-D/A, ~D/A3 and ADC-A
/D, , A/D2 can also be omitted.

Note that the bias component of the line current may be determined according to the required power supply current of the load circuit, and a motor or the like may also be used as the load circuit.

In addition, in FIG. 2, the drive may be performed by a motor or the like, and in addition to the valve V, a damper, a pump, etc. may also be controlled equipment, and a temperature sensor or a fluid leakage sound may be detected. The present invention can be modified in various ways, such as by providing a vibration sensor or the like and providing the detection outputs of these to the communication device CB to be transmitted as monitoring information.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, power is simultaneously supplied only through a two-wire transmission line, and reception based on current values and transmission based on voltage changes can be performed using the same device. In addition, remarkable effects can be obtained in controlling and monitoring various devices to be controlled.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, with FIG. 1 being a circuit diagram and FIG. 2 being a block diagram showing the entire configuration of a communication device. L...Fist/2-wire transmission line, Ql, Q2...Transistor (variable impedance element), Rs+"s...
・Resistor (impedance element), R1+R2+R4
+ R5e * m * Resistor, At + A2 e
m**Differential amplifier, l)/Al, D/Az---
-DAC (digital to analog converter), OP...
・Arithmetic circuit. Patent applicant Masaki Yamakawa (and 2 others) Agent for Yamani-no-Newel Co., Ltd. Procedural amendment (Mutsu) 1981 Patent Application No. 113010 2. Title of invention Communication device 3. Related Patent Applicant Name (Name) (666) Yamatake Honeywell Co., Ltd.
廿3 た力 inertia t-Th1=Illusion power number--...-(1) In the 2nd page, line 16 of the specification, ``are'' is replaced with ``are,'' but such field equipment is and correct it. (2) "1 Pulp" on page 3, line 7 of the same ministry is corrected to "bulbs, etc." (3) Add the following to the next section of ``Naru.'' on page 9, line 7 of the same book. (4) Add the following to the end of "-decode" on page 10, line 8 of the same book. [Or, in the case of an analog signal, extract its change.'' (5) In line 15 of the same page of the same book, change ``showing the entire configuration of the communication device side'' to ``an example showing the entire configuration of the communication device side according to the present invention.'' and correct it. (6) "..." in the same book, page 11, line 13, ", R3...-1 to line 14," is corrected as follows. The same applies to a circuit configuration that directly reads the current value without converting the input signal to a voltage, and the same applies when a variable impedance element such as a constant current diode is used in place of the resistor R1. ,"that's all

Claims (1)

[Claims] A device for receiving a signal indicated by a current value of a line current passing through a two-wire transmission line, comprising: a first variable impedance element inserted in series with the transmission line; and a first variable impedance element connected in series with the variable impedance element. a receiving impedance element, a first control circuit that controls the impedance of the first variable impedance element based on a first reference voltage in a direction to constant the line voltage of the transmission line; A series circuit including a first variable impedance element, a series impedance element connected in parallel to the impedance element, and a second variable impedance element; a second control circuit that controls the impedance of the variable impedance element based on a second reference voltage; a load circuit connected in parallel with the second variable impedance element; and a load circuit that controls the impedance of the series variable impedance element in accordance with a transmission signal. A communication device comprising means for simultaneously changing the first and second reference voltages while maintaining a constant current value.