JPH0729086A - Information transmitting system - Google Patents

Abstract

PURPOSE:To provide an information transmitting system capable of evading the breaking, etc., of a measuring equipment by facilitating the circuit configuration of a terminal equipment, attaining minituarization, reducing a cost and current consumption, preventing the mulfunction of a microcomputer and the breaking of a power source circuit inside a device in a transitional state at the time of turning-on the power source in the device and, moreover, preventing the transmission of an abnormal current value which exceeds its own transmission quantity. CONSTITUTION:The constant current circuit 11 of the terminal equipment is constituted of an arithmetic amplifier OP, a transistor Tr, a resistor R connected to the collector of the transistor Tr and a preservation resistor RR connected between the emitter and ground of the transistor Tr. A voltage Vdd is respectively impressed on the constant current circuit 11 and an information/voltage conversion and voltage amplifier circuit 10 from the power source 22 of a central information monitoring system through a transmission cable 20 and the resistor R of the constant current circuit 11. The protective resistor RR is operated as a current restricting equipment for preventing the overflow of current through the transistor Tr and the resistor R at the time of turning-on the power source in the device.

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 an electric current and transmitting it to a measuring device through 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 the voltage / current conversion circuit,
That is, it is input to the constant current circuit 11. This constant current circuit 1
Reference numeral 1 is composed of an operational amplifier OP, a transistor Tr, and a resistor R connected to the emitter of the transistor Tr, and information S from the information / voltage conversion and voltage amplification circuit 10
Is supplied to one input (+) of the operational amplifier OP. The output signal from the operational amplifier OP is current-amplified by the transistor Tr, and the amplified output flows through the resistor R connected to its emitter, and generates the voltage VR across the resistor R. The voltage VR generated across the resistor R corresponds to the input voltage V of the constant current circuit 11. Since the resistance R has a constant value, the current I ₁ 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 way, the current signal corresponding to the information S from this terminal device is transmitted by the transmission cable 2
Through 0, the information is supplied to the measuring load 21 which is a measuring instrument such as a moisture meter, a thermometer, a pressure gauge in the central information monitoring system, and the information S is displayed.

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. Accordingly, 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 I ₁ flowing in the transistor Tr and the information / voltage conversion and voltage amplification circuit 10.
Current I ₂ flowing through the load, and both currents (I ₁ + I ₂ ) 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 I ₂ is constant, no problem occurs in the basic structure of FIG. , When the detection output of the sensor is digital data, a digital-analog converter is required, and further, in order to improve the explosion-proof safety, the current consumption of the terminal equipment is reduced as much as possible. IC chips such as few microcomputers, digital-analog (D / A) converters, and analog-digital (A / D) converters are often used. In this case, the self-consumption current of the microcomputer, the D / A converter, etc. may fluctuate depending on the environmental temperature and the operating state, which causes a large measurement error.

In order to solve the above problem, as shown in FIG. 8, 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 set to a constant current and Providing via the current / voltage conversion circuit 12 has been proposed. As a result, the current I ₂ flowing through the information / voltage conversion and voltage amplification circuit 10 becomes constant, and the above problem is solved, but there is an irrationality of providing a constant current circuit in duplicate, and the circuit configuration becomes complicated. However, there is a drawback that the terminal device becomes large in size, the cost increases, and the current consumption increases.

Furthermore, since this type of terminal equipment is used as a transmitter installed on site, there are severe restrictions on size, price, environmental stability, explosion-proof safety, etc.
Therefore, it is desired to simplify the circuit configuration as much as possible, reduce the size and cost, reduce the current consumption, increase the environmental stability, and enhance the explosion-proof safety.

[0009]

Therefore, the present inventor has
An information transmission method as shown in FIG. 9 has been proposed for the purpose of providing an information transmission method that simplifies the circuit configuration of a terminal device, reduces the size and cost, and reduces the current consumption (Patent application 4-268198).

Briefly referring to FIG. 9, the information S from a sensor (not shown) of the terminal equipment is input to the information / voltage conversion and voltage amplification circuit 10 and a microcomputer or D arranged in the circuit 10 is connected. Information S at A / A converter
Is converted into a voltage and then amplified by a voltage amplifier to a voltage V having an appropriate magnitude.

The voltage V corresponding to this information S is input to the constant current circuit 11. The constant current circuit 11 comprises an operational amplifier OP, a transistor Tr, and a resistor R connected to the collector of the transistor Tr, and a voltage V corresponding to the information S from the information / voltage conversion and voltage amplification circuit 10. Is supplied to one input (+) of the operational amplifier OP. The output signal from the operational amplifier OP is current-amplified by the transistor Tr, 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 to the measuring load 21 and the information S is displayed.

On the other hand, the power supply voltage Vdd generated from the DC power supply 22 of the central information monitoring system is the transmission cable 2
It is applied to the resistor R of the constant current circuit 11 via 0, but is applied to the information / voltage conversion and voltage amplifier circuit 10 via the resistor R of the constant 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 current I ₁ flowing in the transistor Tr of the constant current circuit 11 and the information / voltage conversion and voltage amplification. It will be divided into the current I ₂ flowing through the load of the circuit 10. Of course, the current (I ₁ + I ₂ ) 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 this configuration, both the current I ₁ flowing through the transistor Tr of the constant current circuit 11 and the current I ₂ flowing through the load of the information / voltage conversion and voltage amplification circuit 10 flow through the resistor R, so that the information / voltage. If there is a load change in the conversion and voltage amplification circuit 10 or if the load current I ₂ flowing in this circuit 10 changes due to information, the load current I ₁ flowing in the transistor Tr of the constant current circuit 11 will increase or decrease by that amount. Therefore, the current I (that is, I ₁ + I ₂ ) transmitted from the terminal device to the measurement load 21 of the central information monitoring system is always kept constant.

Therefore, according to this information transmission system, 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 structure. Therefore, the measurement accuracy is improved. Moreover, since the circuit configuration of the terminal device can be simplified, downsizing and cost reduction can be achieved, and the current consumption can be significantly reduced.
Therefore, environmental resistance stability can be greatly increased, and explosion-proof safety can be further improved. In addition, as described above, even when the detection output of the sensor is digital data, an IC chip such as a microcomputer, a digital-analog converter, an analog-digital converter or the like which consumes less current is used. can do.

However, as a result of further research and experiments conducted by the inventor of the information transmission system having such a configuration,
I found the following:

That is, in the information transmission system shown in FIG. 9, as described above, the information / voltage conversion and voltage amplification circuit 1 is used.
In order to eliminate the influence of the self-consumption current of the microcomputer and the D / A converter in 0 depending on the environmental temperature and the operating state, the microcomputer and the D / A conversion are performed via the resistor R of the constant current circuit 11. A method of supplying an operating voltage (Vdd) to a container or the like is adopted. However, when the power of the device is turned on, the voltage rise of the microcomputer power supply is slow due to the transient characteristics of the constant current circuit 11 and the D / A conversion and voltage amplification circuit, so that an excessive current flows through the transistor Tr and the resistor R. (1) The voltage drop due to the resistor R is large, causing malfunction such as the microcomputer running away. (2) Overcurrent damages the power supply circuit inside the device, mainly the three-terminal regulator. (3) An abnormal current value exceeding the original transmission current is transmitted, and the measuring instrument is damaged. I found that there was a problem.

Therefore, it is an object of the present invention to simplify the circuit configuration of the terminal equipment, to reduce the size and cost, and to reduce the current consumption, and to reduce the power consumption of the equipment inside the equipment in a transient state. The present invention provides an information transmission method capable of preventing the malfunction of the microcomputer and the damage of the power supply circuit, and further, preventing the transmission of the abnormal current value exceeding the original transmission amount and avoiding the damage of the measuring instrument. That is.

[0019]

The above object is achieved by the information transmission system according to the present invention. In summary, the present invention provides (a) a sensor for detecting information of an object to be measured, an information / voltage conversion circuit for converting the information from the sensor into an analog voltage, and a voltage signal from the information / voltage conversion circuit. Terminal device including a voltage / current conversion circuit for converting a current signal into a current signal; (b) a transmission means for transmitting a current signal from the terminal equipment to a measurement load; (c) the voltage / current through the transmission means. A conversion circuit and a power supply for supplying a predetermined operating voltage to the information / voltage conversion circuit; and (d) a resistor connected to the current amplifying means of the voltage / current conversion circuit with the operating voltage from the power supply. The voltage / current conversion circuit and the information / voltage conversion circuit are supplied through an element, and a current signal from the voltage / current conversion circuit is supplied to the terminal device via a protective resistance element connected to the current amplification means. The information transmission system, characterized by transmitting to et the measuring load.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The information transmission system according to the present invention will be described below in more detail with reference to the drawings.

FIG. 1 shows the basic configuration of an embodiment of the information transmission system according to the present invention. In the present embodiment, the information S such as the amount of water, the temperature, and the pressure detected by a 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 voltage, It is amplified to a voltage V of an appropriate magnitude.

The voltage V corresponding to the information S is input to the voltage / current conversion circuit, that is, the constant current circuit 11. The constant current circuit 11 includes an operational amplifier OP and a transistor Tr.
And a resistor R connected to the collector of the transistor Tr, and according to the present invention, the transistor T
A protective resistor R _R is inserted between the emitter of r and ground. The voltage V corresponding to the information S from the information / voltage conversion and voltage amplification circuit 10 is the operational amplifier O of the constant current circuit 11.
Is supplied to one input (+) of P, and also an operational amplifier OP
The output signal from the transistor Tr is current-amplified by the transistor Tr, and the amplified output is taken out from the emitter of the transistor Tr via the resistor R _R.

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 current signal corresponding to is transmitted from the terminal device to the transmission cable 20.
The information S is displayed by being supplied to a current measuring device, that is, a measuring load 21, which is a measuring device such as a moisture meter, a thermometer, and a pressure gauge in the central information monitoring system.

On the other hand, the power supply voltage Vp generated from the DC power supply 22 of the central information monitoring system is applied to the constant current circuit 11 via the transmission cable 20 in the present embodiment. Operating voltage V of amplifier circuit 10
dd is applied via the resistor R of the constant 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 current I ₁ flowing through the transistor Tr and the protection resistor R _R of the constant current circuit 11 and the information / It is divided into the current I ₂ flowing through the load of the voltage conversion and voltage amplification circuit 10. Of course, the current (I ₁ +) flowing through both circuits 10 and 11
I ₂ ) flows through the transmission cable 20 to the measurement load 21 and returns to the power supply 22.

With this configuration, both the current I ₁ flowing through the transistor Tr of the constant current circuit 11 and the current I ₂ flowing through the load of the information / voltage converting and voltage amplifying circuit 10 flow through the resistor R. If there is a load change in the conversion and voltage amplification circuit 10 or if the load current I ₂ flowing in this circuit 10 changes due to information, the load current I ₁ flowing in the transistor Tr of the constant current circuit 11 will increase or decrease by that amount. Therefore, the current I (that is, I ₁ + I ₂ ) transmitted from the terminal 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 or an analog-digital converter which consumes less current.

Further, according to the present invention, as described above, the protection resistor R _{R is provided} between the emitter of the transistor Tr and the ground.
Is inserted. The protection resistor R _R has a function of preventing an excessive current from flowing through the transistor Tr in a transitional state when the device power is turned on. Therefore, this protection resistor R
The sizes of _R and the resistance R can be determined as follows.

The operating voltage Vdd of the circuit 10 varies with the transmitted current I and is represented by the following equation.

Vdd = Vp-R * I Here, the minimum required voltage value of Vdd is Vd _MIN ,
If the maximum current value transmitted is I _MAX , then Vd _MIN = Vp−R * I _MAX .

Therefore, the value of the resistor R is determined by R = (Vp-Vd _MIN ) / I _MAX .

Further, the protection resistor R _R is set so as to satisfy the following condition.

I _MAX > Vp / (R + R _R ) Therefore, for example, Vp = 5.0V, V
dd = 4.5V, and as a I _{MA X} = 20mA, R
= 25Ω and R _R = 225Ω.

As described above, according to the present invention, by inserting the protective resistor R _R between the emitter of the transistor Tr of the constant current circuit 11 and the ground, the transistor Tr and the transistor Tr can be operated in a transient state when the device is powered on. It is possible to prevent an excessive current from flowing through the resistor R. That is, since the protection resistor R _R functions as a current limiter, it is possible to prevent a malfunction such as a runaway of the microcomputer due to a voltage drop in the initial transient characteristics.

According to the results of experiments conducted by the present inventor, it is possible to effectively prevent an excessive current from flowing through the transistor Tr and the resistor R when the power is turned on by inserting the protective resistor R _R having the above size. The voltage rise time of the power supply for the microcomputer can be changed from the conventional 2000 mS to 3
It could be reduced to 0 mS. This completely eliminated runaway microcomputers.

Further, the protection resistor R _R prevents an overcurrent from flowing in the device, thereby preventing damage to electronic parts in the device due to the overcurrent, and further, the original transmission amount through the transmission cable 20. It is possible to prevent an abnormal current value exceeding the above value from flowing to a measuring device such as a moisture meter, a thermometer, a pressure gauge in the central information monitoring system.

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 a 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 provided on the input side of the inverter 51 at the preceding stage and the 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. The signal is sent to a microcomputer provided in the microcomputer 10, the processing is performed in the microcomputer to detect the oscillation frequency, and the detected frequency is converted into a pulse signal corresponding to the concentration of the object to be measured and output.

Further, in FIG. 3, the resistance change type sensor Rh whose electric resistance value changes in accordance with the change of the concentration of the object to be measured such as moisture 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 electric characteristics 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 moisture is used and the same. 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 above 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, the 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 and ZC of the three switches X, Y and Z are the second fixed contacts X1 and 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 oscillation output from the CR oscillation circuit 50, that is, the frequency signal is sent to the microcomputer 60, where it is arithmetically processed to detect the oscillation frequency, and this detection frequency is converted into a pulse signal corresponding to the concentration of the object to be measured. Convert and output.

Usually, 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 the present embodiment, the microcomputer 60 is a memory that includes a counter unit 61 that counts the number of pulses of the input frequency signal F _C or F _R , and a ROM (Read Only Memory) that stores an arithmetic processing program. An arithmetic processing unit that detects a frequency according to the program of the storage unit 62 from the number of pulses in a certain time counted by the unit 62 and the counter unit 61, and converts the detected frequency into a pulse signal corresponding to the concentration of the measured object. 63, a control port 64 for supplying a control command from the arithmetic processing unit 63 to each analog switch X, Y, Z through the respective control lines LX, LY, LZ to control the connection mode of these switches; Part 63
And a parallel input / output port (I / O port) 65 for outputting the pulse signal P ₀ and the strobe signal STR.

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. Further, 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 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. It is sent to the operational amplifier OP of the constant current circuit 11 of FIG.

Parallel I / O of the microcomputer 60
In the present embodiment, a pulse signal P ₀ corresponding to the concentration of the object to be measured such as the amount of water in crude oil is output from the O port 65 at regular intervals, and at the same time, the strobe signal STR having the same period.
Is output. The pulse signal P ₀ is stored in the capacitor C11 via the diode D11 and the resistor R11. That is, the resistor R1 is provided only in the section where the pulse output voltage is at a high level.
The electric charge is charged in the capacitor C11 through 1. 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, assuming that the equation (2) holds similarly, the voltage of the capacitor C11 is obtained. 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 number of pulses 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.

Here, 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.

Also, the one-shot multi-vibrator 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). 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. Therefore, 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 simplified 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 conventional digital-analog converter consumes several mA to several tens of mA, whereas the digital-analog converter of this embodiment has a current consumption of less than 1 mA at the maximum.

Therefore, by adopting the configuration of this embodiment, the environmental resistance stability of the terminal equipment is greatly increased, and
There is a remarkable effect that 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 used, etc. can be arbitrarily changed as necessary.

[0065]

As described above, according to the information transmission system of the present invention, the operating voltage of the terminal equipment for transmitting the information from the sensor to the measuring equipment is converted into the current amplifying means of the voltage / current conversion circuit. The current signal as information from the voltage / current conversion circuit is supplied from the terminal device to the measuring device through the protective resistance device connected to the current amplification means while being supplied through the resistance device connected to the. Therefore, the circuit configuration of the terminal device can be simplified, the size and cost can be reduced, and the current consumption can be reduced, and the malfunction of the microcomputer in the device and the power supply circuit in the transient state when the power is turned on to the device can be reduced. It is possible to prevent the damage of the measuring instrument and further prevent the transmission of the abnormal value exceeding the original transmission amount, thereby avoiding the damage of the measuring device.

[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.

FIG. 9 is an overall configuration diagram showing still another example of the basic configuration of the conventional information transmission system.

[Explanation of symbols]

10 Information / voltage conversion and voltage amplification circuit 11 Voltage / current conversion circuit (constant current circuit) 20 Transmission cable 21 Current measuring device (measurement load) 22 Power supply 50 CR oscillation circuit 51, 52 Schmidt inverter 60 Microcomputer OP operational amplifier R resistance _R R protection resistance Tr transistor

Claims (2)

[Claims] 1. A sensor for detecting information of an object to be measured, an information / voltage conversion circuit for converting the information from the sensor into an analog voltage, and a voltage signal from the information / voltage conversion circuit as a current signal. A terminal device including a voltage / current conversion circuit for converting into a voltage; and (b) transmission means for transmitting a current signal from the terminal device to a measurement load; (c) the voltage / current conversion circuit through the transmission means; A power supply for supplying a predetermined operating voltage to the information / voltage conversion circuit; and (d) an operating voltage from the power supply through a resistance element connected to a current amplification means of the voltage / current conversion circuit. The current signal from the voltage / current conversion circuit is supplied to the voltage / current conversion circuit and the information / voltage conversion circuit, and the current signal from the voltage / current conversion circuit is measured from the terminal device via a protective resistance element connected to the current amplification means. An information transmission method characterized by transmitting to a regular load. 2. The information / voltage conversion circuit 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 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.