JPH09212786A - System for transmitting sensor signal and inclination measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly transmit a sensor signal without being affected by the voltage lowering of a line, thermoelectric power, contact resistance and induction voltage noise, etc., by detecting a signal from a sensor by current value through the use of a power source line. SOLUTION: A 4-20mA current transmitting system is constituted by providing a converting circuit 22 being a converting means between a receiver 20 side and a transmitter 21 side. Then, on the receiver 20 side, the converting circuit is connected to an input terminal 23, connection is executed from the converting circuit to a signal correcting circuit 24 and the signal being 0-4V is outputted from the signal correcting circuit 24 to an output terminal 25. Moreover, a power source E is connected so as to permit current 12 in the reverse direction against current I1 flowing in resistance RL to flow. That is, a circuit is the equivalent one where 24V is applied to the transmitter 21 side by two signal lines, the output of the sensor is converted into 4-20mA in the converting circuit 22 to be returned. Thus, the receiver 20 detects the state of the sensor signal with the two lines for supplying the power source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a wide range of fields such as civil engineering and mechanical engineering, and is used for an inclination measuring instrument equipped with a sensor for detecting a minute angle used for precision measurement of horizontality and inclination measurement. The present invention relates to a current transmission system of up to 20 mA, and more particularly to a transmission system for sending a sensor signal to a receiver at a remote place in a system for monitoring a sensor or controlling by a sensor signal.

[0002]

2. Description of the Related Art Conventionally, in a wide range of fields such as civil engineering and mechanical engineering, precision measurement of horizontality and inclination measurement can be controlled by the same measuring instrument, and direct measurement and measurement on an object to be measured can be performed. There is a so-called servo-type tilt measuring instrument that guarantees absolute horizontality so that telemetry can be performed.

One of the most important problems in servo-type inclinometers is the problem of offset or zero change. Generally, when the level or tilt measuring instrument is actually placed in an absolute horizontal state and indicates an angle, the indicated value is called an offset, and the level or tilt measuring instrument is set horizontally and the indicated value is the minimum value. Then, the phenomenon in which the indicated value changes from the previous horizontal time when it is placed horizontally again after being greatly tilted is called zero change.

As shown in FIG. 4, the servo-type tilt measuring instrument having such a property is mainly composed of a moving coil type instrument 2 housed in a shield case 1.
The moving coil type meter 2 is composed of a fixed portion 3 and a movable coil 4, and the fixed portion 3 is fixed in the shield case 1 and has a magnet that generates a constant magnetic field. The movable coil 4 is supported so as to freely rotate.
When a current is applied to the movable coil 4, a torque is generated in the movable coil 4 due to the interaction between the current and the magnetic field.

The magnitude T of this torque is expressed by T = ± A · B · N · Io. Here, A is the area of the movable coil 4, B is the magnetic flux density, N is the number of turns of the movable coil 4, and Io is the magnitude of the current flowing through the movable coil 4.

The movable coil 4 is structured to rotate until the torque T and the torque due to the inclination of the shield case 1 are balanced.

Although not shown, the movable coil 4 is rotatably supported by a span band so that its center of gravity is shifted downwards and is pendulum-like. By thus supporting the movable coil 4 in a pendulum shape, the torque balance in the servo mechanism described later functions and the tilt angle can be measured.

The span band is a thin band strip material made of a platinum-nickel alloy and having a rectangular cross section, and its rotational force is given by its twisting force.
Compared to the pivot support method, the span band support method
Since there is little backlash and friction, even slight vibrations received by the movable coil 4 can be accurately detected.

The movable coil 4 has arms 5A and 5A extending in the left-right direction perpendicular to the direction of the span band.
B is provided, and the shutters 6A and 6B are attached to the tips of the arms 5A and 5B with the reflection surfaces facing downward. That is,
When the movable coil 4 rotates, the two shutters 6A and 6B, which are in point symmetric positions with respect to the span band, move up and down in opposite directions.

Further, a pair of reflection type photoreflectors Tra and Trd are fixed at positions facing and facing the two shutters 6A and 6B, respectively.

Reflective photoreflectors Tra, Trd
Converts the forward current IF into infrared and converts this into the shutter 6
A photodiode PDa that emits light toward A and 6B,
PDd and phototransistors PTa and PTd that receive the infrared light reflected from the shutters 6A and 6B and convert the light into collector current Ic.

If the forward current IF of the photodiodes PDa and PDd is constant, infrared light of a constant intensity is emitted, so the intensity of the infrared light received by the phototransistors PTa and PTd depends on the reflection type photo reflector Tra. T
It changes depending on the distance between rd and the shutters 6A and 6B.
That is, depending on the magnitude of the collector current Ic of the phototransistors PTa and PTd, the reflection type photoreflector Tr can be obtained.
It has a structure capable of detecting the distances La and Ld between a and Trd and the shutters 6A and 6B.

In assembling this servo type tilt measuring device, the reflection type photo reflectors Tra and Trd are arranged on a substantially circular substrate 7, and supports 8A and 8B are provided from both sides of the substrate 7.
The movable coil type instrument 2 is positioned and attached by. Then, the shutters 6A, 6B and the reflection type photo reflectors Tra, Trd are arranged so that the light emitting surface sides thereof face each other. The moving coil type instrument 2 mounted on the substrate 7
Is completed by mounting it on the base 11 via the base plate 9 and the flange 10, mounting the cover 13 having the receptacle 12 on the top, and covering the shield case 1.

As shown in FIG. 5, the reflection type photoreflectors TRa and TRd thus assembled face the shutters 6A and 6B, and the infrared rays from the photodiodes PDa and PDd. The shutter 6
Phototransistors PTa and PT by reflecting to A and 6B
send to d. That is, the structure is such that the reflection state of light from the shutters 6A and 6B is electrically converted and fed back.

On the other hand, the reflection type photo reflectors Tra and Trd in the assembled servo type inclination measuring device constitute a bridge circuit as shown in FIG.
It operates so as to keep the distance between A and 6B and the reflective photoreflectors TRa and TRd constant.

This bridge circuit, as shown in FIG.
It is composed of resistors RA and RD and phototransistors PTa and PTd, and also has phototransistors PTa and PTd.
In this structure, a variable resistance VRE for adjusting the variation of the above is interposed between the phototransistors PTa and PTd. In addition, the movable coil L and the variable resistor VRo (about 2 kΩ) are connected in series between the resistor RA and the phototransistor PTa and between the resistor RD and the phototransistor PTd, and the variable resistor VRE is connected between the resistors RA and RD. The variable r has a structure in which a resistor r (980 ohm) and photodiodes PDd and PDa are connected in series.

The movable coil L is a movable part of the so-called span band ammeter with its center of gravity displaced, and is a variable resistor VR.
o is a resistor for extracting the output.

A reflection type photoreflector TR in a tilt measuring instrument having a bridge circuit having such a structure.
As shown in FIG. 5, the relationship between a, TRd and the shutters 6A, 6B is such that the center of gravity M1 of the movable coil L forming the movable portion is set to a position lower than the center M2 of the movable portion, and a pendulum shape is formed. It has a hanging structure.

Then, the reflection type photo reflector TRa,
TRd is a reflection type light conversion element in which the phototransistors PTa and PTd and the photodiodes PDa and PDd are integrally packaged, and the photodiodes PDa and PD
Stabilized power supply (12 volt DC) is supplied to d.

If power is not supplied to the tilt measuring device having the bridge circuit, as shown in FIG. 8, when the tilt measuring device itself is tilted to the left, the reflection type photoreflector TRa is provided. The distance between the shutter 6A and the shutter 6B becomes the minimum, and the distance between the reflective photoreflector TRd and the shutter 6B becomes the maximum.

In such a state, when power is supplied to the inclination measuring device having the bridge circuit, as shown in FIG. 9, infrared rays are emitted from the photodiodes PDa and PDd of the reflection type photoreflectors TRa and TRd. Is emitted, hits and is reflected by the shutters 6A and 6B, and is fed back into the bases of the phototransistors PTa and PTd to enter. Phototransistors PTa and PT that obtained infrared rays
As shown in FIG. 7, d is the amount of incident infrared rays is the current I.
a, Id, and collector-emitter voltage VCE
a and VCEd are generated and fed back to the moving coil L side. Then, as shown in FIG. 5, the bridge circuit works so as to obtain the distance La on the shutter 6A side and the distance Ld on the shutter 6B side.

The equilibrium conditions in which the distances La and Ld are the same are as follows: voltage VA = VD, collector-emitter voltage VCEa = VCEd, current IA = ID, and current Io = zero ampere in FIG. That is, voltage (VA-VD) = (VCEa-VC
The relationship of Ed) is established.

At a certain angle, the difference between the voltages VA and VD between the terminals of the resistors RA and RD or the collector-emitter voltage VCE of the two phototransistors PTa and PTd.
The difference between a and VCEd is the output voltage. At the time of inclination, the left side and the right side are normally equal and opposite in polarity, and plus or minus zero is established. Thereby, the shutter 6A,
6B and the reflective photoreflectors Tra and Trd have the same distances La and Ld.

In this way, the infrared rays reflected from the shutters 6A and 6B are converted into electric currents and hooded back while balancing the bridge circuit by using the reflection type photoreflectors Tra and Trd. The minute displacement angle is detected.

[0025]

However, in the above-mentioned conventional servo-type inclination measuring instrument, the voltage drop on the line, the attenuation due to the thermoelectromotive force, the contact resistance, Induced voltage,
There is a problem that the influence on the minute signal extracted cannot be eliminated due to noise or the like.

Therefore, there is a problem to be solved in a transmission system for ensuring the reliability of signals on a transmission line, and in particular for a servo-type inclination measuring instrument which requires the reliability of detected signals.

[0027]

In order to solve the above-mentioned problems, a sensor signal transmission system according to the present invention converts a sensor for detecting displacement or resistance change and the state of the sensor to a sensor signal and sends the sensor signal. A transmitter, a conversion means for converting the sensor signal into a predetermined current value when the sensor signal is in an on state, and a receiver for supplying a power source having a predetermined voltage and current to the sensor, the transmitter and the conversion means by at least two lines According to the present invention, the receiver is provided with detection means for detecting the state of the sensor signal via the two lines for supplying the power.

Further, in the sensor signal transmission system, the conversion means is 4 mA-based on the state of the sensor signal.
The current value is converted to a current value of 20 mA; the conversion means converts the current value to 20 mA when the sensor signal is in the off state, and 4 when the sensor signal is in the on state.
It is to convert into a current value of mA.

The tilt measuring device comprises a pair of shutters that reflect light rays to the left and right sides of a movable coil that is rotatably supported in a pendulum shape, a photodiode that emits light rays in the shutter direction, and a shutter that reflects the light rays. Sensor for detecting a minute angle, comprising a pair of reflective photoreflectors integrally formed with a phototransistor for converting the converted light rays into a current, and a bridge circuit incorporating the phototransistor of the pair of reflective photoreflectors, and the sensor A transmitter for converting the state of the sensor signal to a sensor signal and transmitting the sensor signal, a converting means for converting the sensor signal into a predetermined current value when the sensor signal is in an on state, and a power source comprising a predetermined voltage and current for the sensor, transmitter and converting means. Is supplied by at least two lines to the receiver via two lines for supplying the power. It is by providing the detecting means for detecting the state of the sensor signal Te.

Further, the conversion means provided in this inclination measuring device is 4 mA to 20 m based on the state of the sensor signal.
The current value is converted into a current value of A; the conversion means converts into a current value of 20 mA when the sensor signal is in the off state, and 4 mA when the sensor signal is in the on state.
It is to convert into the current value of.

As described above, since the signal from the sensor is received by the current value on the line for supplying the two power supplies, the configuration is simplified and noises and the like to the signal are prevented, so that a high-performance signal is obtained. Transmission can be maintained.

Further, by adopting this sensor signal transmission in the inclination measuring device, it becomes possible to accurately transmit the signal from the sensor having a minute angle.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sensor signal current transmission system according to the present invention will be described below with reference to the drawings.
As for the inclination measuring device, it has been explained in the prior art, so please refer to that.

4 to 20 depending on the sensor signal current transmission system
As shown in FIG. 1, the mA current transmission method is a transmission method for sending a sensor signal to a receiver at a remote place in a system for monitoring a sensor or controlling by a sensor signal.

That is, in the 4 to 20 mA current transmission system, a conversion circuit 22 as conversion means is provided between the receiver 20 side and the transmitter 21 side.

The receiver 20 side is connected to a conversion circuit via an electric wire resistance RE (250 ohms) to an input terminal 23 for inputting a +24 VDC power source, and the conversion circuit connects the electric wire resistance RF (2
It is connected to the signal correction circuit via 50 ohms) and outputs a signal of 0 to 4 V from the signal correction circuit 24 to the output terminal 25.

The signal correction circuit 24 has a configuration in which a constant current circuit A5, a resistor RG, and a power source E connected in series are connected in parallel to a resistor RL (250 ohm in the embodiment) connected in series with a resistor RF. ing. The power source E is connected so that a current I2 in the opposite direction to the current I1 flowing through the resistor RL flows.

That is, 24 V is transmitted by the transmitter 21 with two signal lines.
To the output side, and the output of the sensor is converted into 4 to 20
It is an equivalent circuit that converts to mA and sends back.

Resistance RE at both ends of the transmitter 21, RF = 25
0 ohm is the resistance of the electric wire, and the receiver 20 side puts the resistance RL = 250 ohm on one side and the voltage between terminals (10 volt)
Has been taken out. A current of 4 mA always flows and resistance R
There is a voltage drop of 1V between the L (250 ohm) terminals.
A voltage of 5 V is obtained at a current of 20 mA, and a voltage of 1 to 5 V is obtained. By the way, in order to return the current of 4 mA to the voltage of 1 V to the voltage of 0 V, the resistance E of the receiver 20 is set to RL = 250.
A reverse current I2 is applied to the ohm to cancel it. When the current I1 flows through the resistor RL, a voltage of (plus) → (minus) polarity is generated, and when the current I2 flows, the voltage of (minus) → (plus) polarity is generated. Therefore, the constant current circuit of the signal correction circuit 24. If the current I2 is adjusted so that the voltage becomes the same at A5, the voltage drop of the resistor RL is canceled. Therefore, 4mA → 0mA, 1-5V → 0-4
V can be realized.

On the transmitter 21 side, a sensor is connected to the conversion circuit 22, and a current Ii = 100 μA flows.

The conversion circuit 22, as shown in FIG.
The A constant current circuit 26, the 100 μA constant current circuit 27, an external power supply 28, and an amplifier 29 are included.

The 4 mA constant current circuit 26 is 24 volt DC
It is a circuit that creates a constant current of 10 V and 4 mA from a power supply, and consists of three terminals so that the current can be adjusted.

The 100 μA constant current circuit 27 inputs 4 mA from the 4 mA constant current circuit 26 and outputs Ii = 100 μA, and is connected to an external sensor, that is, a sensor of a so-called inclination measuring device. That is, since the current value 4 mA is offset, zero (displayed as 4 mA) and disconnection,
Or, when the circuit is opened (zero current), there is an advantage that the state without a signal can be distinguished.

On the transmitter 21 side of the sensor, for example, 0 to 1
00 mv is converted into 4 to 20 mA and transmitted to the receiver 20 side. On the receiver 20 side, insert a resistance of 250Ω, and
The output is obtained by setting the voltage of mA to 1 to 5V. However, it is impossible to discriminate the signal of 1 to 5 V to be input to the control circuit (not shown), that is, the signal in the state where the so-called getter is applied. Therefore,
The signal correction circuit 24 converts the signal into a signal of 0 to 4 V and outputs the signal.

By the way, the sensor is often regarded as a mere displacement or resistance change, not as an energy source. In order to convert the sensor output into a signal, it must be supplied to the power supply. That is, the sensor (transmitter 21 side)
And the receiver 20 are connected by two lines to supply power. In this way, the sensor (transmitter 21 side) and the receiver 2
The 0 side is connected by two lines and 24 V DC is supplied from the receiver 20 side. In most cases 4 mA current transmitter 2
It is supplied as the power on the 1st side. Since the current value of 4 mA is flowing even when the sensor signal is zero, the current value is 4 mA when the signal is zero. Normally, the current is 16 mA at full scale span, and therefore 4 to 20 mA / 0
It becomes 16 mA, and the current is 4 mA.

In this way, the receiver 20 with two lines
The structure is such that power is transmitted in the direction from the side and signals by current are transmitted in the direction returning.

The signal transmission by this current has an advantage that the signal is not affected by voltage drop of one line, thermoelectromotive force, contact resistance, induced voltage noise and the like.

Further, since it is offset by a current of 4 mA, there is also an advantage that it is possible to distinguish the state of no signal when zero (displayed as 4 mA) and disconnection or open circuit (current zero).

The transmitter side 21 converts, for example, 0 to 100 mV into 4 to 20 mA for transmission, and the receiver 20 side has a resistance 2
Insert 50 ohms, current 4-20mA, voltage 1-5V
To get the output. However, as described above, the receiver 2
In order to output from the 0 side, the digitized number such as the voltage of 1 to 5V is returned to the signal of the voltage of 0 to 4V by the signal correction circuit 24.

Next, a tilt measuring instrument adopting a signal transmission method using a 4 to 20 mA conversion circuit will be used.

FIG. 3 shows the ± 4 used in the inclination measuring device.
It shows a ± 20mA conversion circuit, and it has a structure that supplies a power of ± 24V with two lines each by a 3-wire signal line, and detects that the sensor swings counterclockwise. Constant current circuit 30 and minus constant current circuit 31 that detects the sensor swinging clockwise.
And ± 4 mA adjustment circuit 3 for each
It has a structure in which 2, 33 are provided.

Positive constant current circuit (Positive C
The current sink 30 is a Zener diode ZD which mainly supplies the amplification amplifier 34, the Darlington transistor Tr1 and a voltage of + 10V to the amplification amplifier 34.
1 and the signal Vin from the sensor is zero (when the tilt angle is horizontal), the current +4 in the direction of arrow P1.
It has a circuit configuration that allows mA to flow.

Negative constant current circuit (Negative)
The current source 31 is similar to the positive constant current circuit 30 in that the amplifier 35, the Darlington transistor Tr2, and the voltage of −10 V are mainly amplified.
5 and a Zener diode D2 supplied to the sensor 5, and when the signal Vin from the sensor is zero (when the tilt angle is horizontal), a current of -4 mA flows in the direction of arrow P2. The GND line flows in the directions of both arrows P3 and P4 and becomes zero.

In such a circuit configuration, if the sensor of the tilt measuring device is swung clockwise even a little, the Darlington transistor Tr2 operates and the Darlington transistor T
If r1 does not operate, or if it shakes counterclockwise from the horizontal even a little, the Darlington transistor Tr1 operates and the Darlington transistor Tr2 does not operate.

By thus detecting the tilt of the tilt measuring device using the 4 to 20 mA converter, the detected sensor signal can be supplied to a control circuit or the like (not shown) with high accuracy. is there.

[0056]

As described above, the sensor signal transmission system according to the present invention supplies power from two power supply lines and detects a signal from the sensor by a current value using the same two power supply lines. By doing so, there is an effect that the sensor signal can be accurately transmitted without being affected by the voltage drop of the line, the thermoelectromotive force, the contact resistance, the induced voltage noise and the like.

Further, by adopting the sensor signal transmission system based on the current value in the inclination measuring device, the sensor signal detected by the sensor of the inclination measuring device is accurately supplied to the control circuit etc. without being affected by noise or the like. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration for converting a sensor signal according to the present invention into a current value by a 4 to 20 mA conversion circuit.

FIG. 2 is an explanatory diagram showing details of the same 4 to 20 mA conversion circuit.

FIG. 3 is an explanatory diagram of a tilt measuring device that employs the same 4 to 20 mA conversion circuit.

FIG. 4 is a perspective view showing a structure in which a tilt measuring device is disassembled.

FIG. 5 is an explanatory view showing a tilt structure of a tilt measuring device.

FIG. 6 is an explanatory view showing a tilt structure of a tilt measuring device.

FIG. 7 is a circuit diagram in which the inclination of the inclination measuring device is detected by a bridge circuit.

FIG. 8 is an explanatory diagram showing an inclination caused by two shutters.

FIG. 9 is an explanatory diagram showing an inclination caused by two shutters.

[Explanation of symbols]

1 Shield Case 2 Moving Coil Type Instrument 3 Fixed Part 4 Moving Coil 5A, 5B Arms 6A, 6B Shutter 7 Substrate 8A, 8B Support 9 Base Plate 10 Flange 11 Unit 12 Receptacle 13 Cover 20 Receiver 21 Transmitter 22 Converter 22
Input terminal 24 Signal correction circuit 25 Output terminal 26 4mA constant current circuit 27 100μA constant current circuit 28 External power supply unit
29 Amplification section 30 Positive constant current circuit 31 Negative constant current circuit 32 +4 mA adjustment circuit 33 -4 mA adjustment circuit 3
4 Amplification Amplifier 35 Amplification Amplifier Tra, Trd Reflective Photoreflector PDa, PDd Photodiode Ic Collector Current PTa, PTd Phototransistor La, Ld Interval RA, RD Resistor VRE Variable Resistor L Moving Coil VRo Variable Resistor r Resistor M1 Heavy Core M2 Core Ia, Id, Io, IC current VCEa, VCEd Collector-emitter voltage VA, VD terminal voltage Tr1, Tr2 Darlington transistor ZD1, ZD2 Zener diode

Claims (6)

[Claims] 1. A sensor for detecting displacement or resistance change,
A transmitter that converts the state of the sensor into a sensor signal and sends the sensor signal, a conversion unit that converts the sensor signal into a predetermined current value when the sensor signal is in an ON state, and a predetermined voltage and current for the sensor, the transmitter, and the conversion unit. And a receiver for supplying a power source through at least two lines, wherein the receiver is provided with a detection means for detecting the state of the sensor signal via the two lines for supplying the power source. Characteristic sensor signal transmission system. 2. The sensor signal transmission system according to claim 1, wherein the conversion means converts the current value of 4 mA to 20 mA based on the state of the sensor signal. 3. The converting means converts a current value of 20 mA when the sensor signal is in an off state and a current value of 4 mA when the sensor signal is in an on state. 1. The sensor signal transmission system according to 1. 4. A pair of shutters that reflect light rays to the left and right sides of a movable coil that is rotatably supported in a pendulum shape, a photodiode that emits light rays in the shutter direction, and the light rays reflected from the shutters as current. A sensor for detecting a minute angle, which comprises a pair of reflective photoreflectors integrally formed with a phototransistor for conversion and a bridge circuit incorporating the phototransistor of the pair of reflective photoreflectors, and a sensor signal indicating the state of the sensor. A transmitter for converting and sending to a sensor, a converter for converting the sensor signal into a predetermined current value when the sensor signal is in an on state, and at least two power supplies consisting of a predetermined voltage and current for the sensor, transmitter and converter. And a receiver for supplying the sensor signal via two lines for supplying the power source. Inclination measuring device, characterized in that a detecting means for detecting a state. 5. The tilt measuring instrument according to claim 4, wherein the converting means is adapted to convert into a current value of 4 mA to 20 mA based on the state of the sensor signal. 6. The converting means converts a current value of 20 mA when the sensor signal is in an off state and a current value of 4 mA when the sensor signal is in an on state. The tilt measuring device according to item 5.