JPS61109335A - Communication equipment - Google Patents

Abstract

PURPOSE:To transmit stable a data from a transmitter without giving effect of reception of a current value onto a receiver by changing a line voltage through the change of an impedance inserted to one transmission line so as to transmit information without changing the current value flowing to a two- wire transmission line. CONSTITUTION:The line voltage VL of a 2-wire transmission line L is changed by a transmitter TX of a communication equipment, and the change in the current value IL due to the change in the voltage VL is received by a receiver RX. A switch S is inserted in series with one line L2 of the transmission line L and a communication equipment CE having variable impedance elements Z1, Z2 and a control circuit CNT is connected across the switch S. The impedance of the element Z1 is changed by the control of the circuit CNT to make the voltage VL constant and a current IL flowing to the element Z1 is controlled to be constant by the control of the element Z2 at the same time. Then the line voltage Vr is changed without changing the current IL flowing to the transmission line L so as to allow the receiver RX to receive information.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oscillator that performs transmission by changing the value of current flowing through a two-wire transmission line in an industrial process, etc. This article relates to a communication device that is added to a transmission device having a receiver that receives data based on a value, and is used for transmitting and receiving data with a transmitter as necessary.

[Conventional technology]

Conventionally, in industrial measurement, when transmitting the measurement output of a differential pressure transmitter, electromagnetic flow meter, etc. to a remote point, it is generally 4 to 20 minutes.
A unified signal such as mA is used, and the measured value is indicated by the current value of this analog signal, and this current value is received by a receiver.

[Problem that the invention seeks to solve]

However, differential pressure transmitters, electromagnetic flowmeters, etc. are generally installed sparsely over a wide area, and in order to adjust them and check their operating status, staff must make frequent maintenance rounds. However, there has been a demand for a means that can make adjustments, check operating conditions, etc. by remote control using existing equipment.

[Means for solving problems]

In order to satisfy the above-mentioned demands, the present invention is constructed by the following means.

In other words, the transmitter is equipped with a function that improves reception by changing the line voltage of the two-wire transmission line, while the first variable is inserted in series with one line of the two-wire transmission line. an impedance element, a receiving impedance element connected to the variable impedance element in one page column, a first variable impedance element, a series impedance element connected in parallel to the impedance element, and a second variable impedance element. A series circuit in which the impedance of the first variable impedance element is controlled in a direction that constants the voltage between the terminals of the first variable impedance element and the receiving impedance element, and the current value flowing through the series impedance element is constant. 2nd direction
The impedance of the variable impedance element is controlled and the current value flowing through the series impedance element is maintained constant according to the transmission signal.
A communication device is configured by a control circuit that simultaneously controls each impedance of the variable impedance element and changes the voltage between the terminals.

[For production]

Therefore, only the current indicating the signal value passes through the impedance element for reception, which allows reception to be carried out, and transmission to be carried out due to changes in the voltage between the terminals corresponding to the transmission signal. While receiving with the value 1"1 and transmitting with the voltage between the terminals at the same time is possible, it is also possible to obtain a local power supply current within the range of a bias component of, for example, 4 mA through the series impedance element.

Therefore, commands etc. can be given to the transmitter from the communication device, and if the transmitter responds by changing the current value in the form of a pulse, etc., it is possible to receive the command! It becomes possible to know the response status of the l1 transmitter.

Furthermore, since it changes the current flowing through the two-wire transmission line, it is believed that it does not interfere with the reception of the current value by the receiver at all.

[Example of hell]

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

Figure 1 is a block diagram showing the communication device.
1. T! One line of a two-wire transmission line connected via
One side is the line La and the other side is the line Lb, and on the other hand, the first variable impedance element (hereinafter referred to as element) Z
+ is inserted, and a resistor R8 is connected in series as a receiving impedance element, while a series circuit consisting of a resistor Rc as a series impedance element and a second element Z2 is connected in parallel with these. It is connected.

In addition, a control circuit CNT is connected as a power supply load in parallel with the element Z2, and the circuit CNT has an inter-terminal voltage VCE + load side voltage Vc of the resistor Re, and a voltage Vc of the resistor Rs, with the line terminal t2 side as a reference. Given the terminal voltage Vs and the data from the keyboard KB, the control circuit CNT sets the first and second control voltages d1. Zz
For example, the voltage VCE is 10v by controlling the impedance of
, while maintaining the voltage Vc at a constant value of 7V, for example, and displaying the display D such as a character display according to the received value based on the voltage Vs.
A display signal is sent to P.

Here, 1, the current Ic flowing through the resistor RcK is expressed by the following equation.

Therefore, by controlling the impedance of element Zl in the direction of keeping VcF constant, and controlling the impedance of element Z2 in the direction of keeping c as a negative value, and adjusting the current 11 flowing thereto, the load current can be adjusted.

Regardless of the current Ic, the current Ic remains constant, and the following equation holds true.

IL = Is+ II +I2-= Is+ Ic-
'-Is=IL IC... (2) That is, by setting IC equal to the bias component, if the line current IL is, for example, 4 to 20 mA, the current Is flowing through the resistor Rs will be the signal component of 0 to 16 mA. Therefore, the received value υ can be detected by the voltage VS.

Further, when IL is 4 to 20 mA, a maximum power supply current of 4 mA can be freely supplied.

Note that on the oscillator side, which will be described later, a constant current circuit sends out the line current It, so even if the impedance on the line side changes, the current value is not affected.

Regarding the above, when transmitting command data etc. to the transmitter, the control voltage vd1. If Vd2 is changed simultaneously in a pulsed or analog manner, the inter-terminal voltage VCE changes without changing the line current (L), and thereby transmission occurs.

Therefore, for example, while keeping the current Ic at 4 mA,
By increasing or decreasing the voltage VCE, it is possible to transmit by changing the voltage while receiving by the current value.

In addition, on the transmitter side, the line voltage of the two-wire transmission line corresponding to the change in the inter-terminal torlical pressure VCE is compared with a predetermined reference voltage, and the change is extracted and decoded. It is possible to simultaneously transmit and receive current values.

Furthermore, in the case where a change in voltage Vc affects the operation of each load circuit, a voltage stabilizing circuit may be inserted into a portion through which current I2 passes.

I Konoha Power・, Element 2. ．． As 22, C, a transistor,
You can use something that exhibits controllably variable impedance, such as a photocoupler.

FIG. 2 is a block diagram showing the entire configuration of the transmission device,
A two-wire transmission line (hereinafter referred to as a transmission line) consisting of a transmitter TX such as a differential pressure transmitter or an electromagnetic flowmeter, and a power supply B, L2.
A resistor r is inserted in series with the power source B as an impedance element, and the terminal voltage of the resistor r is applied to the receiver RX.

Therefore, the line current It flowing to the transmission path due to t@B
When the oscillator TX changes, for example, in the range of 4 to 20 mA, a corresponding terminal voltage Vr is generated in the resistor r,
When the receiver RX detects this, the signal indicated by the current value is received.

Further, a switch S is inserted in series in the line L2 as one line of the transmission path, and a switch S is connected to both ends of the line L2 as shown in FIG.
Communication device C is connected, and switch S is turned on when not transmitting and receiving, but when transmitting and receiving, switch S is turned off.
Transmission and reception will take place between F and the transmitter TX.

That is, the transmitter TX changes the line current It in an analog manner in a range of 4 to 20 mA depending on the differential pressure or flow rate, etc., but the communication device CE changes the inter-terminal voltage VCE in response to the transmission No. 4. Then, while the current It does not change, the line voltage VL changes according to the change in the voltage vcg, which is expressed by the linear equation of the voltage Vt tt.

VL=VB-It(r+Rt) VCE...1
3) Therefore, VB: Voltage of power supply B RL: Roof resistance of transmission path Therefore, transmission due to voltage change from communication device cE,
The transmitter TX can receive the signal by changing the line voltage VL, and the receiver RX can continue to receive the signal by using the current It.

In addition, the transmission from the transmitter TX to the communication device CE is performed by superimposing a pulse-like current change that changes at high speed on the value of the analog line current ■, so that the striking force λ is enough, and the input side of the receiver RX By inserting an r-wave generator, an integrating circuit, etc. that removes high-speed changes, the receiving condition of the receiver RX does not have a shape V at all.

Note that it is preferable that the pulse-like current change is such that the same change is repeated in the positive and negative directions, and the average value becomes zero.

FIG. 3 (ζ) is a block diagram of the control circuit CNT in FIG.
, Analog-to-digital converter (hereinafter referred to as ADC)
A/, D % Digital to analog converter (hereinafter referred to as D
AC) D/A1, D/A2 and Interface I
/F"+, I/F2 is arranged around the periphery, and these are connected by a bus line. The processor CPU executes instructions in the fixed memory ROM, and predetermined data is transferred to the variable memory IJ.
Control operations are performed while accessing the RAM.

The voltage shown in Figure 1 is cl#i, voltage stabilization part RE.
In addition to being stabilized at G, the local power supply E and (...) are used to supply various parts.

On the other hand, a multiplexer MPX controlled by the processor CPU is provided at the input f of the ADC-A/D, thereby controlling the respective voltages VCE and Vc.

Vs is sequentially and repeatedly selected, each converted into a digital signal by the ADC-A/D, and then applied to the processor CPU. In order to provide control data to /A1 and D/A2, control voltages Vd, Vd2 converted into analog signals are sent out.

FIG. 4 is a flowchart of the control situation by the processor CPU, and shows the multiplexer MPX and ADC-A.
/Dk After carrying out the voltage "VCE acquisition" 101, 'VCE is determined by comparison with the first reference voltage Vrl stored in the fixed memory IJ ROM.
-Vr+? ” 102, and this is N(N
If o), the control voltage Vd1 is corrected according to the value of VCE, and this is repeated when step 102 is Y (YES).

Next, as in step 101, take in the voltage 11Vc.
111 and the same steps as step 102.
7, by comparison with the second reference voltage Vr2? )'V
c:vr2? ``112'' is determined, and when this is N, the control voltage %Vd 2 correction'' 113 is performed as in step 103 until this becomes Y.

-1: After making VCE and Vc constant, the voltage "Vs capture" 12 is carried out in the same manner as in step 101.
1, performs the taku conversion operation ``122'' to decode the pulse signal accordingly, and then sends the taku display signal through the interface I/F l '123
Do the following.

FIG. 5 is a flowchart of transmission control, and after performing the taku control process ``201'' shown in FIG. 4, it is also determined whether or not to transmit data from the keyboard KB.
202, and if this is Y, perform 5 conversion calculation #203 to the transmission data, and then perform the control voltage %vd+・Vd2 simultaneous change'' 204 assuming that the current Ic can change, thereby transmitting. , and repeat steps 201 and subsequent steps.

6 and 7 are block diagrams similar to FIG. 1 showing other embodiments, and in FIG. 6, the resistor Re
is inserted into the line terminal t2 side, and in FIG.
It is the same as in Fig. 1 except that s is inserted to the line terminal tl side.

Note that the control circuit CNT needs to select the detection reference potential of each voltage depending on the insertion position of the resistors Rs and Rc.
Accordingly, the configuration shown in FIG. 3 may be slightly modified.

Therefore, the purpose is achieved with only a single control circuit CNT, and the same #! Since the jcNTid is entirely constructed of digital circuits, the communication situation is stable and miniaturization is easy.

FIG. 8 is a circuit diagram showing an example in which the control circuit is an analog circuit, and the emitter and collector of the transistor Q+ as the first variable impedance element are connected in series with the line terminals tl and t2. At the same time, a resistor Rs is connected in series to the collector side of this as an impedance element for reception, and a voltage divider circuit consisting of resistors R+ and Rz is connected in parallel with these. , resistor R as a series impedance element
A series circuit is connected between the emitter and the collector of the transistor Q2 and the transistor Q2 used as the second variable impedance element.

In addition, in parallel with the transistor Q2, as a load circuit, a voltage dividing circuit including a differential amplifier A+, A2, a resistor Rt + R5, DAC-1)/An, D/A+z, A
Arithmetic circuit OP1 interface I/F consisting of DC/A/D, microprocessor, memory, etc.
lr, ■/F12, and display section DP are connected 9, and the arithmetic circuit OP sends out reference voltages Vr], vr, via DAC-D/An, D/An.

Here, the resistors R+, R2 and the differential amplifier At constitute a part of the control circuit, and the DAC/D/A 11
Based on the reference voltage Vrl from , the terminal voltage ■. E
The impedance of the transistor Q+ is controlled in the direction of keeping the inter-terminal voltage VcF, , constant according to the voltage V1 divided by the resistors R, , R, and thereby the line current 11. The terminal voltage Vcg regardless of the value of
For example, k is maintained at a constant value of IOV.

Further, the resistor R4+ Rli and the differential amplifier A2 also constitute a part of the control circuit, and the load circuit 4jAIJ of the resistor R3 is controlled based on the reference voltage Vr2 from the DAC-D/A12.
'fl(voltage Vc is divided by resistors R4 and R5 and f?
According to the C voltage V2, the impedance of the transistor Q2 is controlled in the direction of keeping the current IcO value flowing through the resistor R3 constant, and the power supply current of each load circuit remains unchanged.
For example, the current Ic is maintained at a constant value of 4 mA.

Therefore, resistors R1 and R2 are set to high resistance values, and this I'
If we ignore the current wire 1 leading to 1-, then the current Is' flowing through the resistor Rs, l5 = 11-Ic, and by setting Ic (i7 equal to the bias component, j
), Is is, for example, only a signal component of O□-1,6+nA, so the terminal voltage Vs of resistor Rs is
//Convert to a digital signal using D11, then! When t is given to the arithmetic circuit OP as a reception signal, the circuit OP sends out a display signal by conversion calculation, and a) this is sent to the display section DP via the interface I/F 11.
It is used to display the received data.

In addition, in FIG. 8, negative feedback is applied to the differential amplifiers AI and A2 by the above operation, and
, V2 and Vrz, the following equation holds true.

Here, Vrl and vr2 are stabilized as long as the data from the arithmetic circuit OP can be kept constant, so VC
K and Vc also become constant, and the following equation is obtained.

That is, Ic remains constant.

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

IL==L+Iz+l344s =11+IC+Is
- Ambiguous (7) Here, if ■ and KiO, then s=■L-IC...(8) Therefore, if ■L is, for example, 4 to 20 mA, Ic=
4 mA (so that ■s = 0 to 16 mA, cuff, it is possible to stably supply a maximum of 4 mA of power supply current to each load circuit without interfering with the reception of the signal indicated by Is.

Regarding the above, when transmitting command data etc. to the transmitter TX, the arithmetic circuit OP changes the reference voltages Vrl and Vrx while keeping the current Ic constant according to the transmission signal. /A12
In order to change the data to, for example, in a pulse-like manner, the inter-terminal voltage VCE changes in a pulse-like manner accordingly, and transmission is thereby performed, and transmission No. 4 is indicated by the pulse code.

That is, in order to keep the current Ic constant, the numerator of equation (6) should remain unchanged. If VCE VC is VR, then the following equation can be obtained from equations (4) and (5).

・　・　・　・　(9) At 0, if we have the following relationship, From equations (9) and (10), the following relationship holds true.

However, since the relationship of equation (11) must be maintained, the ADC/A
, /Do, If the data to the A/D 12 are changed at the same time, it is possible to raise or lower the terminal voltage VcE while keeping the current Ic at 4 mA, for example9, and reception based on the current value is performed. It is hoped that transmission can be carried out by changing the voltage while the voltage changes.

As described above, any data can be sent and received between the transmitter TX and the communication device C, without affecting the reception of the current value by the receiver RX.
It is up to Car to give various commands to the transmitter TX and monitor and check the operating status based on the responses of the transmitter T″X.

However, instead of resistor 1 (18), you can use an impedance element such as a guioto, or directly detect the current value! DJ
A constant voltage diode or the like may be used as the resistors Rc and R3.

In addition, in FIG. 8, other controllable variable impedance elements such as a field effect transistor or a photocoupler may be used in place of the transistor QhQ2, and the DAC
-D/An, D/A1p, the reference voltages Vr+ and Vr2 may be generated by a constant voltage converter or the like, and these may be switched at the time of transmission.

Various modifications can be made, such as determining the amount of change depending on the situation.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the line voltage is changed by changing the impedance inserted into one line of the transmission line without changing the current value flowing through the two-wire transmission line, and transmission is stopped. Therefore, transmission and reception with the transmitter can be freely performed without affecting reception of the current value by the receiver at all, and remarkable effects can be obtained in commands to the transmitter, monitoring of the transmitter, and the like.

[Brief explanation of the drawing]

The figures show embodiments of the present invention, in which Fig. 1 is a block diagram of a communication device, Fig. 2 is a block diagram showing the entire transmission device, and Fig. 3 is a block diagram showing the entire transmission device.
The figure is a block diagram of the control circuit, Figures 4 and 5 are flowcharts of the control situation, Figures 6 and 7 are block diagrams similar to Figure 1 showing other embodiments, and Figure 8 is the control circuit. This is a circuit diagram when constructed using an analog circuit. L...2-wire transmission line, Z, , Z,... element (variable impedance element), Rs, Rc...
Resistor (impedance element), CNT...φ control circuit, CPU...processor, ROM...fixed memo +1, RAM...variable memory, MPX...war...
Multiflexor, A/D. A/Dr1...ADCC analog/deisotal converter), D/A+, D/A2, D/Au,
D/AI2...Exposure/DAC (digital to analog converter), KB...Keyboard, DP...
Display section, Qi+Q2''...Transistor (variable impedance element), Rs+R3...Resistor (
impedance element), R1, R2, R4, R5...
・Resistor, A+, A2...Differential amplifier, OP・
... Arithmetic circuit, TX ... Transmitter, RX ...
Receiver, CE...Communication i#', Position, IL...Line current, VL...Line voltage, VcE...Terminal voltage, Ic...Input current.

Claims (1)

[Claims] A transmission device comprising: a transmitter that transmits by changing a current value passing through a two-wire transmission line, and also receives according to a change in line voltage of the transmission line; and a receiver that performs reception according to a current value of the transmission line. A first variable impedance element inserted in series with one line of the transmission path, a reception impedance element connected in series with the variable impedance element, and the first variable impedance element and the impedance element. In contrast, a series circuit including a series impedance element and a second variable impedance element connected in parallel, and the first variable The second
controlling the impedance of the variable impedance element of the first and second variable impedance elements while simultaneously controlling the impedance of the first and second variable impedance elements while maintaining a constant value of the current flowing through the series impedance elements according to the transmission signal; A communication device comprising: a control circuit that changes a voltage between terminals.