JPH0457254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a receiving device that receives a signal indicated by a current value and controls a device to be controlled, such as a valve, in an industrial process or the like.

[Prior art]

In industrial processes, etc., when remotely controlling valves, etc., a receiving device called a positioner is generally installed, but such field equipment can change the current within a range of, for example, 4 to 20 mA from a central control device. A signal is transmitted based on the current value, and the receiving device receives the signal and performs control according to the current value.

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

There is.

[Summary of the invention]

The present invention has the purpose of fundamentally solving such drawbacks of the conventional technology, and has the purpose of
Note that a unified signal such as 20mA originally represents a numerical value in a range of 0 to 16mA, etc., and includes a bias component such as 4mA. impedance elements are inserted in series, and the impedance of the variable impedance element is controlled in the direction of making the line voltage of the transmission line constant, and a series circuit consisting of the impedance element in series with these elements and a second variable impedance element is connected in parallel. A load circuit is connected in parallel with the second variable impedance element, and the bias component is used as a power source for the receiving device. By measuring the voltage of the receiving impedance element and detecting the received signal from the current flowing through it, it is extremely effective in making it possible to supply power only through the two-wire transmission line. The purpose of the present invention is to provide a receiving device that has the following characteristics.

〔Example〕

Hereinafter, details of the present invention will be explained with reference to figures showing examples.

Fig. 1 is a circuit diagram, in which a two-wire transmission line L connected via line terminals t ₁ and t ₂ consists of lines L ₁ and L ₂ , and a first variable impedance element. The emitter and collector of transistor Q ₁ are inserted in series, and a resistor R _S is connected in series on the collector side of this transistor as an impedance element for reception, while a resistor R is connected in parallel with these. ₁ and _R2 are connected, and a series circuit is also connected between the emitter and collector of a resistor _R3 as a series impedance element and a transistor _Q2 used as a second variable impedance element.

In addition, in parallel with the transistor Q ₂ , an integrated circuit power supply stabilization circuit REG and a resistor R ₄ ,
Voltage divider circuit with R ₅ and differential amplifier A ₁ ,
_A2 is connected as a load circuit, and an arithmetic circuit consisting of analog-to-digital converters (hereinafter referred to as ADCs) A/ _D1 , A/ _D2 , a microprocessor, memory, etc. is connected via a power supply stabilization circuit REG.
OP and a digital/analog converter (hereinafter referred to as DAC) D/A are also connected as load circuits.

Here, the resistors R ₁ , R ₂ and the differential amplifier A ₁ constitute a first control circuit, and based on the reference voltage V _r1 from the power supply stabilization circuit REG, the transmission line L
The impedance of the transistor Q ₁ is controlled in a direction to keep the line voltage V _L constant according to the voltage V ₁ obtained by dividing the line voltage V _L by the resistors R ₁ and R ₂ .
Thereby, the line voltage V _L is maintained at a constant value of 10V, for example, regardless of the value of the line current I _L.

Also, resistors R ₄ , R ₅ and differential amplifier A ₂ are
Configuring the second control circuit, the power supply stabilization circuit REG
The voltage obtained by dividing the load circuit side voltage V _C of resistor R ₃ by resistors R ₄ and R ₅ based on the reference voltage V _r2 from
The impedance of transistor Q ₂ is controlled in the direction of keeping the value of current I _C flowing through resistor R ₃ constant according to V ₂ , and the current I _C is controlled to be 4 mA, for example, regardless of the power supply current of each load circuit. It is maintained at a constant value.

Therefore, the current I ₁ passing through the resistors R ₁ and R ₂ =
Since V _L /(R ₁ + R ₂ ) is a constant value, the resistor R _S
The current I _S flowing through is I _S = I _L − I (I _C + I ₁ ),
By setting (I _C + I ₁ ) equal to the bias component, I _S becomes only a signal component of, for example, 0 to 16 mA, so the terminal voltage of resistor R _S is converted to a digital signal by ADC/A/D ₁ . , This is given as a setting value to the arithmetic circuit OP, and the drive device described later
If the actual measurement value from DR is similarly converted by ADC/A/D ₂ and given to the arithmetic circuit OP, the circuit OP will send out a control signal by control calculation, and this will be converted into an analog signal by DAC/D/A. Convert to
By controlling the opening degree of the valve by applying it to an electro-pneumatic converter E/P, which will be described later, the opening degree of the valve is set so that the set value and the actual measurement value match.

In addition, in FIG. 1, negative feedback is applied to the differential amplifiers A ₁ and A ₂ by the above operation,
Since V ₁ = V _r1 and V ₂ = V _r2 , the following equation holds true.

V ₁ =V _L R ₂ /R ₁ +R ₂ =V _r1 ∴ V _L =V _r1 (1 + R ₁ /R ₂ ) ...(1) V ₂ =V _C R ₅ /R ₄ +R ₅ =V _r2 ∴ V _C =V _r2 (1+R ₄ /R ₅ )...(2) Here, since V _r1 and V _r2 are stabilized, V _L and V _C are also constant, and the following equation is obtained.

I _C =V _L −V _C /R ₃ ...(3) That is, (I _C +I ₁ ) is constant.

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

I _L = I ₁ + I ₂ + I ₃ + I _S = I ₁ + I _C + I _S ... (4) Here, since I ₁ and I _C are constant, I _S = I _L − (I _C + I ₁ ) ... (5) Therefore, if I _L is, for example, 4 to 20 mA, I _C
By setting +I ₁ =4 mA, I _S =0 to 16 mA, and a maximum power current of AmA can be stably supplied to each load circuit without interfering with reception of the signal indicated by I _S.

Note that on the central control device side, the line current I _L is sent out by a constant current circuit, so even if the input impedance of the receiving device changes, the current value is not affected.

In other words, the current value of the signal (4
~20mA) is performed by a constant current circuit. This constant current circuit operates so that a set constant current value always flows, and when the above signal current is set to a value between 4 and 20 mA, that signal current value is currently flowing. If the current value is greater than the current value, the voltage must increase in order to increase the current, so the terminal voltage is increased. This terminal voltage is the line voltage of the transmission line.
V _L , the receiving device detects this rise in line voltage V _L and transistor Q ₁ increases the current.
It acts to increase I _S and is controlled to keep the line voltage V _L constant. At this time, line current I _L
increases by the amount that the receiving device current I _S increases.

In the constant current circuit on the control device side, the voltage increase operation continues until the line current I _L reaches the set signal current value, and the voltage increase stops when the output current reaches the set signal current value. . At this time, the current value output from the constant current circuit is the set signal current value, and the current value of the receiving device I _S increases by the current value increased by the setting of the constant current circuit. .

FIG. 2 is a block diagram showing an example of the entire configuration of the receiving device according to the present invention. The output from the receiving device RE shown in FIG. P becomes a pressure according to the output of the receiving device RE, and the driving device such as an air cylinder
This is sent to the DR, which drives the valve V to control the opening degree, and the current opening degree is detected as an actual measurement value by a potentiometer connected to the drive shaft, and is given to the receiving device RE. It's summery.

Therefore, power is supplied simultaneously using only the two-wire transmission line, and the required amount of wire and the number of man-hours for installation are significantly reduced, resulting in a reduction in equipment costs.

However, in FIG. 1, the transistors Q ₁ ,
Other controllable variable impedance elements such as field effect transistors and photocoupler may be used in place of _Q2 , and the same applies to circuit configurations that directly read the current value without converting the input signal to voltage using the resistor _R. The same effect can be obtained even if a variable impedance element such as a constant current diode is used in place of the resistor _R3 . Furthermore, without using the power supply stabilization circuit REG, the reference voltage V _r1 ,
Generate V _r2 and load circuit all transistor Q ₂
may be connected in parallel.

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.

Further, in FIG. 2, the device may be driven by a motor or the like, and in addition to the valve V, a damper, a pump, etc. may also be controlled equipment, and the present invention can be modified in various ways.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the power required on the receiving side is simultaneously supplied using only the two-wire transmission line, eliminating the need for a power supply line and significantly reducing line equipment costs. However, remarkable effects can be obtained in various receiving devices that receive signals indicated by current values.

[Brief explanation of the drawing]

The figure shows an embodiment of the present invention, and FIG. 1 is a circuit diagram;
FIG. 2 is a block diagram showing the entire configuration of the receiving device. L...Two-wire transmission line, _Q1 , _Q2 ...Transistor (variable impedance element), R _S , _R3 ...Resistor (impedance element), _R1 , _R2 , _R4 , _R5 ...
...Resistor, REG...Power stabilization circuit, A ₁ , A ₂ ...
...Differential amplifier.

Claims (1)

[Claims] 1. A receiving device that supplies a signal current from a constant current circuit of a control device to a two-wire transmission line and receives a signal indicated by the current value of a line current flowing through the two-wire transmission line, a series circuit of a first variable impedance element and a receiving impedance inserted in series with the transmission line; and a series circuit of a first variable impedance element and a receiving impedance inserted in series with the transmission line; a first control circuit for controlling the impedance of the impedance; and a series circuit of a series impedance element and a second variable impedance element connected in parallel to the series circuit of the first variable impedance element and the receiving impedance. a second control circuit that controls the impedance of the second variable impedance element so as to keep the value of the current flowing through the series impedance element constant; and a second control circuit connected in parallel to the second variable impedance element. and a receiving circuit that receives a signal indicated by the current value of the line current by detecting a voltage generated across the receiving impedance element.