JPH0696382A - Information transmission system - Google Patents

Abstract

PURPOSE:To provide the information transmission system which is reduced in size and cost and also decreased in current consumption by simplify the circuit constitution of a terminal equipment. CONSTITUTION:The constant current circuit 11 of the terminal equipment consists of an operational amplifier OP, a transistor(TR), and a resistor R connected to the collector of the TR, and the voltage Vdd from a center power source 22 is applied to the constant current circuit 11 and an information/voltage converting and voltage amplifying circuit 10 through a transmission cable 20 and the resistance of the constant current circuit 11. Consequently, the current I flowing through the transmission cable 20 from the power source 22 can be shunt into a current I1 flowing to the TR and a current I2 flowing to the load of the circuit 10 after flowing through the resistor R. Consequently, even if the load current I2 of the circuit 10 varies depending upon information, the load current I1 flowing to the TR increases by the variation quantity and the current sent from the terminal equipment to a center load 21 for measurement is held invariably constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information transmission system for converting information detected by a remote terminal device into electric current and transmitting it to a measuring load via a transmission cable.

[0002]

2. Description of the Related Art For example, in a petroleum plant, a terminal device equipped with a sensor for detecting information such as water content, temperature, and pressure of crude oil is installed in a tank at a remote location where crude oil is stored. The converted information is converted into a current value of 4 to 20 mA in the terminal device, and is transmitted via a transmission cable, for example, a moisture meter, a thermometer of a central information monitoring system,
It is sent to a measuring load, which is a measuring device such as a pressure gauge, and it is constantly monitored whether or not the crude oil in the tank is maintained in an appropriate state.

FIG. 7 shows the basic configuration of a conventional information transmission system of this type. The information S such as the amount of water, the temperature, and the pressure detected by the sensor of the terminal device (not shown) is input to the information / voltage conversion and voltage amplification circuit 10, and after the information S is converted into the voltage, the voltage of an appropriate size is obtained. It is amplified to V.
The voltage V corresponding to this information S is input to the constant current circuit 11. This constant current circuit 11 is composed of an operational amplifier OP, a transistor Tr, and a resistor R connected to the emitter of the transistor Tr. It is supplied to one input (+) of OP. Operational amplifier OP
The output signal from is current-amplified by the transistor Tr, the amplified output of which flows through the resistor R connected to its emitter, generating a voltage VR across it. This resistance R
The voltage VR generated across both ends corresponds to the input voltage V of the constant current circuit 11. Since the resistance R has a constant value, the current I1 flowing through the transistor Tr and the resistance R is determined by the input voltage V.

After converting the information S detected by the sensor into an appropriate current value of 4 to 20 mA in this manner, the current signal corresponding to the information S from this terminal device is transmitted by the transmission cable 20.
The information S is displayed by being supplied to the measuring load 21 which is a measuring instrument such as a moisture meter, a thermometer, and a pressure gauge in the central information monitoring system.

On the other hand, a central information monitoring system such as 2
The power supply voltage Vdd generated from the 4V power supply 22 is applied to the constant current circuit 11 and the information / voltage conversion and voltage amplification circuit 10 via the transmission cable 20, respectively. As a result, the current I flowing from the power source 22 through the transmission cable 20 is the load of the constant current circuit 11, that is, the current I1 flowing in the transistor Tr and the information / voltage conversion and voltage amplification circuit 10.
The current I2 flowing through the load is also divided into two, and both of these currents (I1 + I2) flow through the transmission cable 20 to the measurement load 21 and return to the power supply 22.

Here, when the information / voltage conversion and voltage amplification circuit 10 is composed of a simple analog circuit or the like and the flowing current I2 is constant, no problem occurs in the basic structure of FIG. If the detection output is digital data, a digital-analog converter is required, and in order to improve the explosion-proof safety, the current consumption of the terminal equipment is reduced as much as possible. An IC chip such as a digital-analog converter or an analog-digital converter is often used. In this case, the circuit becomes complicated and the load changes or the load current flowing in the circuit changes due to information. That causes a large error.

[0007]

FIG. 8 shows a conventional basic configuration generally used to solve the above problems. That is, the difference from the basic configuration of FIG. 7 is that the power supply voltage Vdd supplied from the power supply 22 of the central information monitoring system to the information / voltage conversion and voltage amplification circuit 10 of the terminal equipment is a constant current and current / voltage conversion circuit. It is a point to supply via 12. As a result, the current I2 flowing through the information / voltage conversion and voltage amplification circuit 10 becomes constant, and the above problem is solved.

However, in the configuration shown in FIG. 8, there is an absurdity that the constant current circuit is provided in duplicate, and the circuit configuration becomes complicated, the terminal device becomes large, the cost increases, and the current consumption increases. There is a drawback to Furthermore, since this type of terminal equipment is used as a transmitter installed in the field, there are severe restrictions on size, price, environmental stability, explosion-proof safety, etc. Therefore, the circuit configuration should be as simple and compact as possible. It is desired to reduce the consumption current, reduce the current consumption, increase the environmental resistance stability, and enhance the explosion-proof safety.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an information transmission system which simplifies the circuit configuration of a terminal device, reduces the size and cost, and reduces the current consumption.

[0010]

The above object is achieved by the information transmission system according to the present invention. In summary, the present invention includes a sensor for detecting information of an object to be measured, and an information / voltage conversion unit for converting information from the sensor into an analog voltage and a voltage signal from the information / voltage conversion unit. Terminal equipment including voltage / current conversion means for converting into a current signal, transmission means for transmitting a current signal from the terminal equipment to a measurement load, and the information / voltage conversion means and the voltage / current through the transmission means A power supply for supplying a predetermined operating voltage to the converting means, and the operating voltage from the power supply is
The voltage / current converting means and the information /
This is an information transmission system characterized in that it is supplied to a voltage conversion means.

[0011]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the basic configuration of an embodiment of the information transmission system according to the present invention. Also in this embodiment, the information S such as the amount of water, the temperature, and the pressure detected by the sensor (not shown) of the terminal device is input to the information / voltage conversion and voltage amplification circuit 10, and after the information S is converted into the voltage, it is appropriate. It is amplified to a voltage V of a large magnitude. The voltage V corresponding to this information S is input to the constant current circuit 11. The constant current circuit 11 includes an operational amplifier OP, a transistor Tr, and this transistor T.
It consists of a resistor R connected to the collector of r,
The voltage V corresponding to the information S from the voltage conversion / voltage amplification circuit 10 is supplied to one input (+) of the operational amplifier OP. The output signal from the operational amplifier OP is a transistor Tr.
Is amplified by current, and its amplified output is directly taken out from its emitter.

After the information S detected by the sensor is converted into an appropriate current value of 4 to 20 mA, the information S is converted into the information S.
The current signal corresponding to is supplied from the terminal device through the transmission cable 20 to the measuring load 21 which is a measuring device such as a moisture meter, a thermometer, a pressure gauge in the central information monitoring system, and the information S is displayed. Become.

On the other hand, a central information monitoring system, for example, 2
The power supply voltage Vdd generated from the 4V power supply 22 is applied to the resistor R of the constant current circuit 11 via the transmission cable 20 in this embodiment, but this constant voltage is applied to the information / voltage conversion and voltage amplification circuit 10. It is configured to be further applied via the resistor R of the current circuit 11. Therefore, the current I flowing from the power source 22 through the transmission cable 20 flows through the resistor R of the constant current circuit 11 as it is, and then the constant current circuit 1
It is divided into a current I1 flowing through the first transistor Tr and a current I2 flowing through the load of the information / voltage conversion and voltage amplification circuit 10. Of course, the current (I1 + I2) flowing through both circuits 10 and 11 flows through the transmission cable 20 to the measurement load 21 and returns to the power supply 22.

With such a configuration, both the current I1 flowing through the transistor Tr of the constant current circuit 11 and the current I2 flowing through the load of the information / voltage conversion / voltage amplification circuit 10 flow through the resistor R, so that the information / voltage conversion and If there is a load change in the voltage amplification circuit 10 or if the load current I2 flowing in this circuit 10 changes due to information, the load current I1 flowing in the transistor Tr of the constant current circuit 11 will increase or decrease by that amount, and the terminal The current I (that is, I1 + I2) transmitted from the device to the measurement load 21 of the central information monitoring system is always kept constant.

Therefore, according to the present embodiment, it is possible to prevent the occurrence of a measurement error without duplicating the constant current circuit in the terminal equipment and complicating the circuit configuration. Therefore,
Measurement accuracy is improved. Moreover, since the circuit configuration of the terminal device can be simplified, it is possible to reduce the size and cost, and further, it is possible to significantly reduce the current consumption. Therefore, environmental resistance stability can be greatly increased, and explosion-proof safety can be further improved. In addition, it is possible to deal with the case where the detection output of the sensor is digital data, and it is possible to use an IC chip or the like such as a microcomputer, a digital-analog converter, an analog-digital converter, etc., which consumes less current.

Next, a specific example of the information / voltage conversion and voltage amplification circuit 10 of this embodiment corresponding to the case where the detection output of the sensor is digital data will be described.

For example, as a sensor for detecting the concentration of a component in the liquid phase such as the amount of water in crude oil, a moisture (gas) sensor having a capacitance change type electric characteristic or a resistance change type electric Moisture (gas) sensors that have specific characteristics are often used. As shown in FIGS. 2 and 3, these sensors include, for example, two inverters 51 and 52 connected in series, such as a C-MOS type Schmitt inverter, and a resistor R1 inserted in the feedback circuit of the preceding-stage inverter 51. When,
Similarly, it is used as an oscillating frequency determining element of the CR oscillating circuit 50, which is composed of a capacitance element (capacitor) C1 connected to the input side of the inverter 51 in the preceding stage.

That is, in FIG. 2, a capacitance change type sensor Ch whose capacitance changes in accordance with a change in the concentration of an object to be measured such as moisture is shown as an input side of the inverter 51 at the preceding stage and a capacitance element. CR oscillator circuit 5 inserted in series with C1
0, and the capacitance of the sensor Ch changes in accordance with the change in the concentration of the object to be measured, so that the oscillation frequency of the CR oscillation circuit 50 is correspondingly changed. No, it sends the signal to a microcomputer, performs arithmetic processing in the microcomputer to detect the oscillation frequency, converts the detected frequency into a pulse signal corresponding to the concentration of the measured object, and outputs the pulse signal.

Further, in FIG. 3, a resistance change type sensor Rh whose electric resistance value changes in accordance with a change in concentration of an object to be measured such as water is provided in the CR oscillation circuit 50 described above.
The resistor R1 inserted in the feedback circuit of the inverter 51 at the previous stage
Instead of, insert as a resistance element for determining the oscillation frequency,
The CR oscillating circuit 50 is configured so that the electric resistance value of the sensor Rh changes according to the change of the concentration of the object to be measured.
The oscillating frequency of the R oscillating circuit 50 is correspondingly changed, and C
It detects the oscillation frequency of the R oscillator circuit 50 and provides a pulse output corresponding to that frequency.

Further, as shown in FIG. 4, a sensor GS having an electric characteristic in which the capacitance component C and the electric resistance component R are changed according to the change in the concentration of the object to be measured such as water is used, and the same is used. The first, second and third three switches X of the configuration,
When used as a capacitance change type sensor by Y and Z, the sensor GS is connected in series between the input side of the preceding inverter 51 and the capacitance element C1 as shown in FIG. Further, when it is used as a variable resistance type sensor, as shown in FIG. 3, the sensor GS is switched and connected so as to be inserted in the feedback circuit of the inverter 51 in the preceding stage in place of the resistor R1, and the above-mentioned diagram is used. A configuration is also proposed in which the CR oscillation circuit 50 shown in FIGS. 2 and 3 is configured.

The first, second and third switches X, Y,
Z has one movable contact XC, YC, ZC and two fixed contacts X0 and X1, Y0 and Y1, Z0 and Z1, respectively, and the first switch X has a movable contact XC whose resistance R2 is for removing DC voltage. Is connected to the connection point of the electrostatic capacitance element C1 and the first fixed contact X0 is not connected, and the second fixed contact X1 is connected to the input side of the inverter 51 at the preceding stage. In addition, the movable contact YC of the second switch Y is connected to the other terminal of the sensor GS, and the first fixed contact Y0 is connected to the connection point between the resistor R2 for removing the DC voltage and the electrostatic capacitance element C1. , The second fixed contact Y1 is the third switch Z
Of the second fixed contact Z1. Furthermore, the third
The switch Z has a movable contact ZC whose front is the inverter 5
1 is connected to the output side, and the first fixed contact Z0 is connected to the resistor R1.
It is connected to the.

In the above structure, three switches X,
When the movable contacts XC, YC, ZC of Y and Z are connected to the first fixed contacts X0, Y0, Z0 side as shown in the drawing, the resistor R1 is inserted in the feedback circuit of the inverter 51 at the preceding stage, The sensor GS is connected in series with the capacitance element C1 on the input side of the inverter 51 of the preceding stage, and the sensor G
A capacitance measurement type circuit configuration in which a resistor R2 for removing a DC voltage is connected in parallel between both ends of S, and the oscillation frequency changes in accordance with the capacitance value of the same sensor GS as in FIG. The oscillator 50 is configured.

On the other hand, the movable contacts XC, YC, ZC of the three switches X, Y, Z are the second fixed contacts X1, Y.
1 and Z1 side, the sensor GS is inserted in the feedback circuit of the inverter 51 of the preceding stage instead of the resistor R1, and the resistor R2 for removing the DC voltage on the input side of the inverter 51 of the preceding stage is the first resistor. Shorted by switch X at 1,
Since the capacitance element C1 is connected to the input side of the inverter 51 at the preceding stage through the first switch X, the CR oscillator 50 whose oscillation frequency changes according to the electric resistance value of the sensor GS as in FIG. To be done.

The oscillating output from the CR oscillating circuit 50, that is, the frequency signal is sent to the microcomputer 60, where it is arithmetically processed to detect the oscillating frequency, and the detected frequency is converted into a pulse signal corresponding to the concentration of the object to be measured. Convert and output.

Normally, C- is used as the inverters 51 and 52.
A MOS type Schmitt inverter is used, and the CR oscillation circuit 50 outputs a pulse signal whose frequency changes in accordance with a change in the electrostatic capacitance value of the sensor GS or a change in the electric resistance value, and the pulse signal is sent to the microcomputer 60. . In this example, the microcomputer 60 includes a counter unit 61 that counts the number of pulses of the input frequency signal F _C or F _R.
And a storage unit 62 including a ROM (Read Only Memory) storing an arithmetic processing program, and a storage unit 6 based on the number of pulses within a fixed time counted by the counter unit 61.
2 detects the frequency according to the program and converts the detected frequency into a pulse signal corresponding to the concentration of the object to be measured, and a control command from the arithmetic processing unit 63 to control lines LX, LY, LZ. Through a control port 64 for supplying the analog switches X, Y, Z to control the connection mode of these switches, and a parallel input / output port (I) for outputting the pulse signal P ₀ and the strobe signal STR from the arithmetic processing unit 63. / O port) 65.

The operation mode of the C-MOS type Schmitt inverters 51 and 52 will be briefly described as follows.
Both Schmitt inverters have two threshold voltages, a high level threshold voltage V _TH and a low level threshold voltage V _TL , and generate a high level output voltage V _H when the input voltage is lower than the high level threshold voltage V _TH. In addition, when the input voltage reaches the high level threshold voltage V _TH , the output voltage switches from the high level V _H to the low level V _L , and the low level is maintained until the input voltage drops to the low level threshold voltage V _TL. Of the output voltage V _L is held, and when the input voltage drops to the low level threshold voltage V _TL , the output voltage switches from the low level V _L to the high level V _H. Therefore, C
The R oscillating circuit 50 outputs a pulse voltage having a cycle corresponding to charging / discharging of the electrostatic capacity element C1 or the electrostatic capacity element C1 and the series circuit of the sensor GS.

The pulse signal P ₀ and the strobe signal STR output from the parallel I / O port 65 of the microcomputer 60 are converted into analog voltage signals by the simple digital-analog converter shown in FIG. Is sent to the operational amplifier OP of the constant current circuit 11 of FIG.

Parallel I / of the microcomputer 60
In this example, from the O port 65, the pulse signal P ₀ corresponding to the concentration of the measured object such as the amount of water in crude oil is output at regular intervals, and at the same time, the strobe signal STR having the same period is output. The pulse signal P ₀ is a diode D11 and a resistor R
It is stored in the capacitor C11 via 11. That is, the capacitor C11 is charged with electric charge through the resistor R11 only in the section where the pulse output voltage is at a high level. The diode D11 is a diode for preventing a reverse current for preventing the electric charge charged in the capacitor C11 from being discharged when the pulse output is at a low level.

On the other hand, the strobe signal STR is supplied to the first one-shot multivibrator MM1. The first one-shot multivibrator MM1 is activated when the strobe signal STR changes from the high level to the low level, that is, when the strobe signal STR falls, so that the output of the strobe signal STR is at the low level. Therefore, the same operation is performed (however, the output of the second one-shot multi-vibrator MM2 operates at the low level when the output of the first one-shot multi-vibrator MM1 changes from the high level to the low level). Therefore, the first and second switches SW1 and SW
2 is in the off state as shown.

Now, assuming that the pulse width of the pulse signal P ₀ is t1 (high level time) and the voltage value at the high level is V, 1
Assuming that the voltage of the capacitor C11 becomes Vc by charging the capacitor C11 with one pulse, the following equation holds.

Vc = V (1−e ^{−t1 / C11 · R11} ) (1) When t1 << C11 · R11, the above equation (1) can be expressed as follows.

Vc = V (t1 / C11R11) (2) When N pulses are output in one cycle, it is assumed that the equation (2) holds similarly, the voltage of the capacitor C11. Vc1 can be expressed by the following equation.

Vc1 = V (Nt1 / C11 · R11) = N (Vt1 / C11 · R11) (3) Therefore, the voltage Vc1 proportional to the pulse number N is stored in the capacitor C11.

When N pulses are output, the strobe signal STR changes from high level to low level. The fall is the first one-shot multi-vibrator MM
1 is detected, and one pulse Vs1 having a pulse width of time constant t2 = R12 · C12 is output. The output pulse Vs1 from the one-shot multivibrator MM1 turns on the first switch SW1 for a time t2, and a part of the electric charge charged in the capacitor C11 is transferred to the capacitor C14. If the voltage of the capacitor C14 at that time is Vc2, the total charge Q becomes Q = C11.Vc1 = (C11 + C14) .Vc2 ... (4), and if C11 >> C14, then Vc2 = Vc1. The charging voltage Vc1 of the capacitor C11 is transferred to the capacitor C14 as it is.

Since the capacitance of the capacitor C14 is very small, the voltage of the capacitor C14 changes due to the influence of the leakage current of the first switch SW1, the capacitance between contacts, the input impedance of the amplifier circuit AMP, and the bias current. , It is necessary to pay sufficient attention to their selection. For example, it is necessary to select a switch that has the smallest leakage current between contacts and has the smallest capacitance between contacts.

The one-shot multivibrator M
It is also necessary to take a sufficient time for the pulse width t2 of M1 to minimize the time during which the voltage of the capacitor C14 changes. For example, if the voltage Vc2 of the capacitor C14 is Vc2 >> Vc1 in the previous cycle, the total charge Q'of the capacitors C11 and C14 is the first when the first switch SW1 is in the ON state.
Capacitor C when the switch SW1 of is on
11, when the voltage of C14 is Vc3, Q '= C11.Vc1 + C14.Vc2 = (C11 + C14) .Vc3 (5). Even in this case, the voltage of the capacitor C11 is held in the capacitor C14. That is, Vc1
In order for = Vc3 to be satisfied, it is necessary to use in the voltage range (Vc1 to Vc2) where C11 · Vc1 >> C14 · Vc2 is satisfied.

However, for example, in the case of continuous measurement, there is no sudden change, and there is a gradual change, so it is not necessary to satisfy the above equation (5), and C11> Only the condition of> C14 should be satisfied.

First one-shot multivibrator M
When the output pulse of M1 falls, the first switch SW
1 is turned off, the second one-shot multivibrator MM2 is activated at the same time, and the time constant t3 = R13 · C.
One pulse Vs2 having a pulse width of 13 is output. The output pulse Vs2 from the one-shot multivibrator MM2 turns on the second switch SW2 for the time t3, the electric charge charged in the capacitor C11 is rapidly discharged, and the voltage of the capacitor C11 becomes 0V. This is the capacitor C1 due to the pulse output of the next cycle.
Since 1 is recharged, the zero point is corrected. Also, note that the first switch S
Since the second switch SW2 is turned on at the same time when W1 is turned off, the charge of the instantaneous capacitor C14 may be discharged by this operation. Therefore, it is preferable to insert, for example, a CR delay circuit in the preceding stage of the control line for the second switch SW2. As with the first switch SW1, it is necessary to select the second switch SW2 that has the smallest leakage current between contacts and the smallest capacitance between contacts.

Waveforms of the above-mentioned signals STR and P ₀ , output waveforms V of the one-shot multivibrators MM1 and MM2
FIG. 6 shows voltage waveforms Vc1 and Vc2 of s1 and Vs2 and capacitors C11 and C14.

The analog signal Vc2 thus converted by the simple digital-analog converter is amplified by the amplifier circuit AMP to an appropriate size and the constant current circuit 11 is supplied.
Is supplied to one input (+) of the operational amplifier OP.

In this way, the information detected by the sensor is converted into C
The R oscillation circuit 50 converts the pulse signal into a pulse signal, the microcomputer 60 detects the frequency of the pulse signal, converts the pulse signal into a binary pulse signal corresponding to the concentration of the object to be measured such as the amount of water, and outputs the binary pulse signal at regular intervals. However, if this pulse data is configured to be directly converted into an analog voltage output by using a simple digital-analog converter with an extremely simple circuit configuration, the circuit configuration of the terminal device is greatly simplified,
Therefore, it is possible to reduce the size and cost, and
The current consumption is extremely low. Incidentally, the current consumption of the conventional digital-analog converter is several mA to several tens of mA, whereas the maximum current consumption of the digital-analog converter of this example is less than 1 mA. Thus, by adopting the configuration of this example, the environmental resistance stability of the terminal device is greatly increased, and the explosion-proof safety is further improved.

In the above embodiments, the case where the present invention is applied to a petroleum plant has been mainly described, but it goes without saying that the information transmission system according to the present invention is not limited to this. Also, not only information such as the amount of water in crude oil, but also the concentration of water in the gas phase such as humidity, the concentration in the liquid phase such as the amount of water in lubricating oil, and other various gases and liquids The present invention can also be applied to the case of measuring the concentration of a certain component. Furthermore, the above embodiments are merely examples of the present invention, and the circuit configuration, the elements to be used, etc. can be arbitrarily changed as necessary.

[0044]

As described above, according to the information transmission method of the present invention, it is possible to reliably prevent the occurrence of measurement error without the need to provide the terminal device with a double constant current circuit. Therefore, the measurement accuracy is increased and the circuit configuration can be simplified, so that the size and cost can be reduced, and the current consumption can be significantly reduced.
As a result, there is a remarkable effect that environmental stability is significantly increased and explosion-proof safety can be further enhanced. Furthermore, it can be applied to the case where the detection output of the sensor is digital data, and in this case, the circuit configuration can be simplified by using a microcomputer with low current consumption, a simple digital-analog converter, etc. And cost can be reduced, and current consumption can be significantly reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a basic configuration of an embodiment of an information transmission system according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of a CR oscillation circuit including, as an oscillation frequency determining element, a sensor applicable to the information / voltage conversion and voltage amplification circuit of the information transmission system of the present invention shown in FIG.

3 is a circuit diagram showing another specific example of a CR oscillation circuit including a sensor applicable to the information / voltage conversion and voltage amplification circuit of the information transmission system of the present invention shown in FIG. 1 as an oscillation frequency determining element.

FIG. 4 is a circuit configuration diagram showing still another specific example of the CR oscillation circuit including a sensor applicable to the information / voltage conversion and voltage amplification circuit of the information transmission system of the present invention shown in FIG. 1 as an oscillation frequency determining element. is there

5 is a simplified digital type used in the information / voltage conversion and voltage amplification circuit of the information transmission system of the present invention shown in FIG.
It is a circuit diagram which shows one specific example of an analog converter.

FIG. 6 is a waveform diagram showing voltage output in each part of the digital-analog converter of FIG.

FIG. 7 is an overall configuration diagram showing an example of a basic configuration of a conventional information transmission system.

FIG. 8 is an overall configuration diagram showing another example of the basic configuration of the conventional information transmission system.

[Explanation of symbols]

 10 Information / voltage conversion and voltage amplification circuit 11 Constant current circuit 20 Transmission cable 21 Measurement load 22 Power supply 50 CR oscillation circuit 51, 52 Schmitt inverter 60 Microcomputer OP operational amplifier R resistance Tr transistor AMP amplification circuit MM1, MM2 One shot multi Vibrator SW1, SW2 switch

Claims (3)

[Claims] 1. An information / voltage conversion means for converting information from the sensor into an analog voltage, and a voltage signal from the information / voltage conversion means into a current signal. A terminal device including voltage / current converting means for converting, a transmitting means for transmitting a current signal from the terminal device to a measuring load, and the information / voltage converting means and the voltage / current converting means through the transmitting means. A power supply for supplying a predetermined operating voltage, the operating voltage from the power supply is passed through the impedance element connected to the current amplifying means of the voltage / current converting means to the voltage / current converting means and the information / voltage converting means. An information transmission method characterized in that it is supplied to a means. 2. The information / voltage conversion means detects a CR oscillating circuit including the sensor as a frequency determining element, a frequency of an oscillation output of the oscillating circuit, and detects the detected frequency as the information of the object to be measured. And a pulse signal voltage output from the arithmetic and control unit is accumulated every one period to be converted into a voltage signal, and the converted voltage signal 2. An information transmission system according to claim 1, further comprising a digital-analog conversion means for amplifying and outputting as an analog voltage signal. 3. The sensor has electrical characteristics such that a capacitance component, an electrical resistance component, or both components change according to the concentration of a certain component in a gas phase or a liquid phase. Information transmission method.