JPH07103759A - Digital inclination measuring instrument - Google Patents

Abstract

PURPOSE:To eliminate the zero-point change of a sensor by connecting a variable resistor between a plurality of reflection-type photo reflectors of the bridge circuit of an inclination sensor, connecting a power supply between the connection points of the intermediate tap and the resistor. and then adjusting the variable resistor. CONSTITUTION:A servo-type inclination sensor 1 feeds back the unbalance of output of reflection-type photo reflectors Tra and Trd to a movable coil 17 for balancing torque when a case is inclined and then the coil 17 follows the rotation of the case. Each emitter of the reflectors Tra and Trd is connected to both terminals of a variable resistor VR and the intermediate tap of a resistor VR is connected to one terminal of a power supply Vs and the connection point of resistors R1 and R2 is connected to the other edge of a power supply Vs, where the zero-point change of the sensor 1 can be eliminated by adjusting the resistor VR and minimizing the bridge output voltage to the coil 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a servo-type tilt sensor that has both functions of a high-precision digital level and a general-purpose digital tilt measuring device, which is used in a wide range of fields such as civil engineering and mechanical engineering. The present invention relates to a digital tilt measuring instrument.

[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 has been a demand for an absolute levelness-guaranteed tilt measuring device that enables remote measurement.

A servo type inclination sensor developed by the same inventor as the present invention is disclosed in, for example, Japanese Patent Laid-Open No. 41110607.
As disclosed in Japanese Patent Publication, the accuracy is higher than that of various conventional tilt sensors, the configuration is relatively simple, and
Since it has excellent characteristics such as being less susceptible to the influence of an external magnetic field, etc., it is considered to be the mainstream of future tilt sensors in line with the above demand.

However, the obstacle to the practical use of the servo type tilt sensor is that the zero change is large. Generally, a zero change is a phenomenon in which the reading changes from the previous level when the level or tilt sensor is leveled, the reading is adjusted to the minimum value, and then it is tilted largely and then placed again horizontally. That is.

Since most of the conventional inclination measuring devices generate a zero change due to a temperature change because of poor temperature characteristics, a zero adjusting mechanism is provided without exception.

The mechanism of the zero change occurrence of the servo type tilt sensor has not been clarified yet, but as a result of research by the present inventor, it can be explained as follows.

First, the general structure of the servo type tilt sensor and the servo mechanism which is the basis of its operation will be described. As shown in FIGS. 6 and 7, the servo type tilt sensor includes a magnet 15 that generates a magnetic field, a yoke 16 that forms a path for magnetic fluxes φ1 and φ2 from the magnet 15, and a magnetic flux φ.
1 and φ2, a movable coil 17 rotatably mounted by being supported by a span band like a pendulum, shutters 18 and 19 as two reflectors attached to the left and right ends of the movable coil 17, and a reflective type Photo reflector 2
0 and 21, and a bridge circuit 22 formed as shown in FIG.

The reflection type photoreflectors 20 and 21 are fixed inside the case which is the outer shell of the servo type inclination sensor, and are inclined so as to follow the case. Therefore, the gaps g1 and g2 between the reflective photoreflectors 20 and 21 and the rotatable shutters 18 and 19 are variable.

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 applied 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 17 can be accurately detected.

As shown in FIG. 7, the movable coil 17 is adjusted so that its center of gravity G is lower than the center O by Δy in the Y direction. That is, the movable coil 17 is rotatably supported in the form of a pendulum suspended by the span band. By thus supporting the movable coil in a pendulum shape, the torque balance in the servo mechanism functions and the tilt angle can be measured.

The reflection type photoreflectors 20 and 21 are composed of photodiodes and phototransistors. The infrared rays are output from the photodiodes of the reflection type photoreflectors 20 and 21 toward the shutters 18 and 19, respectively.
The infrared rays reflected by 8 and 19 are input to the bases of the respective phototransistors to flow the photocurrent Ic.

The photocurrent Ic of each phototransistor of the reflection type photoreflectors 20 and 21 changes as shown in FIG. 9 depending on the distance from the shutter. In the servo type tilt sensor, since the linear portion of the relative photocurrent-distance curve is used, the gaps g1 and g2 are set to about 0.5 mm. In this portion, the photocurrent becomes small when the reflective photoreflector and the shutter are close to each other.

FIG. 10 shows a voltage-current curve representing the relationship between the collector-emitter voltage V _CE of the phototransistor and the photocurrent Ic, with the light amount Ee [mW / cm ² ] of infrared rays as a parameter. is there.

The bridge circuit 22 includes phototransistors Tra and Trd of the reflection type photoreflectors 20 and 21, resistors R1 and R2, a movable coil 17, and an output resistor Ro.
And a power supply Vs.

A power supply Vs is connected between the connection point of the emitters of the phototransistors Tra and Trd and the connection point of the resistors R1 and R2. Also, the phototransistor Tr
A series circuit of the movable coil 17 and the output resistor Ro is connected between the connection point of the collector of a and the resistor R1 and the connection point of the collector of the phototransistor Trd and the resistor R2.

In the bridge circuit 22, collector-emitter voltage V _CE of each of the phototransistors Tra and Trd _.
Be V _CE a and V _CE d, and the voltages of the resistors R1 and R2 are V
_{Assuming A} and V _D , the output voltage Vo of the movable coil 17 is Vo = V _CE a−V _CE d = V _A −V _D.

The balance condition of the bridge is V _A · V _CE d = V _D · V _CE a.

The operation of the servo type tilt sensor having the above structure will be described. First, when the case of the servo type tilt sensor is tilted to the right when the power is not turned on, the reflection type photoreflectors 20 and 21 are shown in FIG.
Although it tilts with the case as shown in, shutters 18 and 1
9 is held horizontal until it collides with the surfaces of the reflective photoreflectors 20, 21.

Therefore, when the power is turned on, the reflection type photo
The relative photocurrent Ia of the deflector 20 increases and the voltage V_CEa is reduced
A little, on the other hand, the relative photocurrent I of the reflective photoreflector 21.
d decreases and voltage V_CEd increases. So V_CEd-V
_CEa = -Vo or V_CEa-V _CEMoveable by d = Vo
A current Io flows through the ill 17. Allowed by this current Io
A torque is generated to rotate the moving coil 17 in the direction of the arrow.
It

The magnitude T of the torque is represented by T = ± A · B · N · Io. Here, A is the area of the movable coil 17, B is the magnetic flux density, and N is the number of turns of the coil.

The movable coil 17 rotates until the torque T and the torque due to the inclination of the case are balanced, so-called torque balance occurs, and the gap g1 and the gap g2 are automatically controlled so as to be equal as shown in FIG. It

When the servo type tilt sensor is horizontal, the output current Io oscillates alternately in the positive and negative directions.
The difference between the positive peak value Io ⁺ and the negative peak value I ⁻ is zero. Thereby, the movable coil 17 is pulled in the X-axis direction. This state is called a state in which the servo is operating, and the shutters 18 and 19 are ready to rotate following the rotation of the case.

When the case is tilted from this state, a difference occurs between the voltage V _CE a of the phototransistor Tra and the voltage V _CE d of the phototransistor Trd as described above, and the current Io due to this difference Vo causes the moving coil 17 to move. And as a result, the shutters 18, 19 are reflected by the reflective photoreflector 2.
Rotation is performed so that the gaps g1 and g2 with respect to 0 and 21 are made equal.

Therefore, even if the case is rotated by 0 to 360 degrees, the shutters 18 and 19 are the reflection type photoreflector 2.
Following the rotation of the case, the gaps g1 and g2 between 0 and 21 are kept equal. On the other hand, the output voltage Vo outputs a voltage corresponding to the tilt angle. Such torque balance is due to the pendulum-like structure in which the center of gravity G of the movable coil is displaced as described above.

As described above, the servo-type tilt sensor operates by the servo mechanism. In this case, the servo-type tilt sensor is leveled to adjust the reading to zero, tilted by a certain angle, and then leveled again. When returned, the indicated value should return to zero, but why does the so-called zero change that does not return occur?

In order to elucidate the generation mechanism of the zero change in the servo-type tilt sensor, the conventional servo-type tilt sensor is horizontally and horizontally at 10 ° and 15 °.
FIG. 1 shows the results of measuring the voltage and current of each part of the bridge circuit 22 for each case of inclination of 30 ° and 30 °.
3 shows.

The points of particular interest in this measurement data are that V _CE a and V _CE d at the time of horizontal are both 8.45 V, and Ia and Id are −4.23 mA and −4.
It shows almost the same value as 18 mA.

Although the variation in the performance of the phototransistor is larger than that of a general transistor, the reason why the measurement result is as described above is that the movable coil 17 automatically selects the distance between the shutter and the reflection type photoreflector by the servo mechanism. However, it is considered that V _CE a and V _CE d and Ia and Id are made equal to each other by making the relative light conversion rates of the reflection type photoreflectors different from each other.

Based on the above measurement data, as shown in FIG. 10, a load line corresponding to each inclination angle is drawn on the V _CE -Ic curve.

As a result, it can be seen that the operating point of the load line is deviated when the servo type tilt sensor is tilted.
Such delusion of the operating point of the load line means that the load line does not return to its original position when the servo type tilt sensor is returned from the tilted state to the horizontal state. This is considered to be the cause of the zero change.

In order to verify the above hypothesis, as shown in FIG. 14, each relative light conversion rate-distance characteristic curve Q of the left and right reflection type photoreflectors of the conventional servo type tilt sensor.
1 and Q2 were drawn symmetrically with respect to the center of the moving coil.

In FIG. 14, the straight line m is the distance g1, g
2 shows a horizontal reference line where 2 are equal and both are 0.5 mm. A straight line n indicates a state in which the movable coil is tilted with respect to the horizontal reference line m by automatic control when the servo-type tilt sensor is tilted.

Here, the straight line n and the left and right characteristic curves Q1, Q
When straight lines that pass through the intersections q1, q2, q3, and q4 with 2 and are parallel to the horizontal reference line m are drawn, those straight lines fall within the area indicated by the diagonal lines. This area is a dead zone area, that is, an area where an operating point offset occurs.

If the intersection points q1 to q4 are not in symmetrical positions, it is impossible to obtain zero by subtraction. Therefore, it is considered that the larger the dead zone area, the larger the offset and the larger the deviation of the operating point.

[0035]

DISCLOSURE OF THE INVENTION The present invention provides a digital tilt measuring device capable of performing ultra-precision horizontal level measurement and tilt measuring with the same measuring device, and also capable of direct mounting and remote measuring. The purpose is to provide a servo-type tilt sensor that guarantees absolute levelness without any change of zero, and thus provides an error of 1 with a minimum reading of 0.001 degree.
There is a technical problem to be solved in realizing a digital tilt measuring instrument with an accuracy within%.

[0036]

In order to solve the above problems, in a digital inclination measuring instrument according to the present invention, a movable coil type instrument has a fixed portion fixed in a case so that the movable coil of the movable coil type instrument is fixed. The center of gravity is shifted downward by a span band so that it can be pivotally supported like a pendulum, and reflectors are fixed on both sides of the movable coil in the direction perpendicular to the span band direction, and light is emitted toward the reflector and reflected light. A pair of reflection type photoreflectors for detecting the distance to the reflection plate are fixed to the case by approaching the reflection plate, and a bridge circuit is formed by the pair of reflection type photoreflectors and two resistors. When the movable coil is formed in the center of the bridge circuit and the case is tilted, the imbalance of the outputs of the two reflection type photoreflectors is fed to the current of the movable coil. A digital tilt measuring instrument comprising a servo-type tilt sensor in which torque is balanced by backing and the movable coil follows the rotation of the case, wherein the bridge circuit of the servo-type tilt sensor is A variable resistor is connected between two reflection type photoreflectors, and a power supply is connected between the intermediate tap of this variable resistor and the connection point of the above two resistors, and this variable resistor is adjusted. By doing so, the operating point of the load line drawn on the voltage-current characteristic curve of each of the reflection type photoreflectors is stabilized, thereby eliminating the zero change of the servo type inclination sensor.

Further, the digital inclination measuring device according to the present invention may be configured by replacing the variable resistor with two fixed resistors each having a resistance value on both sides of the adjusted intermediate tap.

[0038]

By adjusting the resistance values on both sides of the center tap of the variable resistor to obtain the minimum value of the output voltage, delusion of the operating point of the load line drawn on the voltage-current curves of the two phototransistors can be prevented. Eliminate and thus eliminate the zero change.

After adjusting the variable resistor, the variable resistor is
2 equal to the adjusted resistance on both sides of the center tap
Replaced by two fixed resistors.

The digital inclination measuring instrument having the servo type inclination sensor having the above-mentioned structure has the minimum horizontal reading of 0.0.
It is possible to measure with a high accuracy of 1% at 01 degree.

When the case of the servo-type tilt sensor is tilted, the reflective photoreflector rotates following the case.
Then, one of the reflective photoreflectors tries to reduce the distance from the facing shutter, and the other reflective photoreflector tries to increase the distance to the facing shutter. As a result, an imbalance occurs between the photoelectric conversion outputs of the two reflective photoreflectors, and a current corresponding to the tilt angle flows through the moving coil.

The torque generated by this current balances the tilt torque of the case, and as a result, the movable coil rotates following the case. The output current of the moving coil is extracted and displayed as a voltage proportional to the angle.
Therefore, the servo-type tilt sensor operates as a normal inclinometer.

As described above, the digital inclination measuring instrument according to the present invention can perform high-precision measurement of the levelness as a level and can also perform normal inclination measurement as an inclinometer.

[0044]

Embodiments of the digital inclination measuring device according to the present invention will be described below. As shown in FIG. 1, a digital tilt measuring device according to the present invention includes a servo-type tilt sensor 1 having no zero change, a chopper stabilizer-type differential amplifier circuit 2, an LP filter circuit 3, which are features of the present invention.
Linearization circuit 4, polarity inversion circuit 5, and VF conversion circuit 6
The frequency divider 7, the counter circuit 8, the multiplexer 9, the decoder 10, the display circuit 11, the power supply transformer 12, and the voltage stabilizing circuit 13 are mainly configured.

In addition to the above, a transmitter / receiver 14 for telemetry is optionally provided.

The minimum reading of the digital tilt measuring instrument according to the present embodiment is ± 0.001 degree (3.6 at a temperature of 0 to 70 ° C.).
Sec), and this error is guaranteed within 1%. Further, the temperature drift shows an astonishing value of 00 sec 04 / ° C.

Such high performance is realized by the present invention for the first time without a zero change servo-type tilt sensor 1.
This is due to the differential amplifier circuit 2 having a small temperature drift and the LP filter circuit 3.

The output of the servo type tilt sensor 1 is 3 V / 30 degrees when the series resistance Ro of the moving coil is 8.2 KΩ.
It is 6.2 V / 75 degrees, and the minimum value is 0.1 mV / 0.0
It is 01 degrees. Details of the servo-type tilt sensor 1 will be described later.

The differential amplifier circuit 2 is a chopper stabilizer amplifier using two operational amplifiers and has a temperature error of Δ.
Vos / ΔT = 0.01 to 0.05 μV / ° C. Selected from the components. If the temperature error is 0.02 μV / ° C., the increase in ΔVos when the temperature rises from 25 ° C. to 70 ° C. by 45 ° C. is 0.02 × 45 = 0.9 μV.

Therefore, the minimum read value 0.001 at horizontal level
The measurement error of the degree is 0.9 μV ÷ 0.1 mV = 0.9%. Such a value cannot be obtained by the conventional servo type tilt sensor.

The LP filter circuit 3 removes the chopper noise generated in the differential amplifier circuit 2. The output voltage from the LP filter circuit 3 is converted by the linearization circuit 4 into an angular voltage in the range of ± 90 degrees by the voltage / angle curve 4a.

The polarity reversing circuit 5 inverts the polarity of the voltage depending on the direction of the inclination angle. The output voltage of the polarity inverting circuit 5 is converted into a frequency in the VF conversion circuit 6. Also,
The output of the polarity reversing circuit 5 is supplied to the display circuit 11 to form the sign of the angle.

The VF conversion circuit 6 has an angle of 0 to 74 degrees 59.
Minutes are converted at 6.2V, and angles 0 to 59 minutes 59 seconds are converted at 1V.

The output of the VF conversion circuit 6 is the display circuit 11
Is supplied to the counter circuit group 8 while being supplied to the counter display group 11a, divided into 3.6 / 100 by the frequency divider 7.

The counter circuit group 8 is composed of a decimal counter for each first digit of the indication value of the angle minute and second and a hexadecimal counter for each second digit of the indication value of minute and second.

The count value of each counter of the counter group 8 is sent to the decoder 10 via the multiplexer 9. The decoder 10 decodes each count value of angle minutes and seconds,
It is sent to the display circuit 11.

The display circuit 11 digitally displays the angle in 6 digits (99 ° 59'59 ") according to the count value. The display circuit 11 has a portion for displaying degrees and a portion for displaying minutes and seconds. Are composed of separate circuits.

With the above configuration, the servo-type tilt sensor 1 having no zero change, the differential amplifier circuit 2 having a small temperature error, and the LP filter circuit 3 have an absolute horizontal level of 1.
We were able to realize a high-precision digital inclination measuring instrument guaranteed within%.

Next, the structure of the servo type tilt sensor 1 which is a feature of the digital tilt measuring device according to the present invention will be described in detail. In the servo type tilt sensor 1, like the conventional servo type tilt sensor described above, the fixed portion of the moving coil type instrument is fixed in the case, and the center of gravity of the moving coil of the moving coil type instrument is shifted downward by the span band. A pair of pendulums are supported rotatably, a reflector is fixed on both sides of the movable coil in the direction perpendicular to the span band direction, light is emitted toward the reflector, and the distance from the reflector is detected by the reflected light. The reflection type photoreflector is fixed in the case close to the reflection plate, and a bridge circuit is formed by the pair of reflection type photoreflector and two resistors, and a moving coil is connected to the center of the bridge circuit. Is configured.

The servo type tilt sensor 1 operates by the servo mechanism described above, and when the case is tilted, the unbalance of each output of the above two reflection type photoreflectors is fed back to the current of the moving coil to generate a torque. It is balanced so that the moving coil follows the rotation of the case.

A feature of the servo type tilt sensor 1 according to the present invention is that it has a bridge circuit configured as shown in FIG. 2 so as to eliminate the zero change based on the above research results.

In this bridge circuit, the phototransistor T
The emitters of ra and Trd are connected to both ends of the variable resistor VR, and the intermediate tap of the variable resistor VR is connected to one end of the power source Vs. The other end of the power supply Vs is connected to the connection point of the resistors R1 and R2.

The voltages on both sides of the center tap of the variable resistor VR are V1 and V2, and the voltages on both arms of the bridge are V1.
Letting a and Vd be Va = V1 + V _CE a Vd = V2 + V _CE d.

The adjustment of this bridge circuit is extremely simple. That is, by adjusting the variable resistor VR,
The values of V1 and V2 may be adjusted so that the values of Va and Vd are equal, and as a result, the output voltage Vo may be minimized.

FIG. 3 shows measured data of voltage and current of each part of the servo type tilt sensor 1 having the bridge circuit shown in FIG. In addition, Tr
a, Trd V _CE a-Ia straight line, V _CE d-Ia straight line, V
Drawing the a-Ia straight line and the Vd-Id straight line is as shown in FIG.

As can be seen from this figure, in any of the load line groups, the operating points a, d, and P remain immobile, and all the load lines are tilted around the operating point. That is, since the operating point does not move, each straight line returns to its original state even if the horizontal state → the inclined state → the horizontal state is maintained, and therefore zero change does not occur.

FIG. 5 shows the inclination angle-output voltage characteristic of the servo type inclination sensor 1 using the output resistance Ro as a parameter.

The digital inclination measuring device according to the present invention uses the servo type inclination sensor 1 and the chopper stabilizer type differential amplifier 2 having a small temperature drift as follows, as compared with the conventional one. It has excellent performance. (1) We have realized a digital inclination measuring instrument that has both the functions of a digital level and an inclination measuring instrument that guarantee absolute horizontality, which did not exist in the past.

(2) The minimum reading is 0.
At 001 degrees, the error is ± 1.0%, the maximum read value is ± 90 degrees, and the error is ± 0.001%. (3) As for the temperature characteristics, a surprising value of 0 ″ 04 / ° C. was obtained.

(4) The output of the servo type tilt sensor 1 is
A highly stable voltage of ± 6.2 V / ± 90 degrees was obtained. (5) Since there is no zero change, the yield of the servo type tilt sensor 1 is high.

Furthermore, since the angle-output voltage characteristic of the digital inclination measuring device according to the present invention is 3 V / 30 degrees, the minimum reading value 0.001 degrees is converted into a voltage of 0.1 mV. Therefore, the diameter of the servo-type tilt sensor 1 is 30 m.
If m, the displacement due to the rotation of 0.001 degree is 15 ×
Tan 0.001 ° = 0.2618 μm. The converted value of voltage / displacement in this case is 381.97 μV / 1 μm
And is extremely accurate.

Therefore, the digital inclination measuring instrument according to the present invention is not only used as a level and inclination measuring instrument transistor, but also as a highly accurate transit for displacement measurement in civil engineering, length measurement and surveying in mechanical engineering, etc. It can be widely applied to.

[0073]

As described above, the present invention realizes a servo type tilt sensor without a zero change with a simple structure, whereby a minimum reading value is 0.001 degree at a temperature of 0 to 70 ° C., for example. A highly accurate digital level and tilt measuring instrument with an error of 1.0% was realized. As a result, there is an extremely excellent effect that the high-precision measurement of the levelness and the inclination measurement can be performed by one measuring device.

Furthermore, the present invention can be widely applied to measuring instruments for displacement measurement, length measurement, and surveying in a wide range of fields, and therefore contributes greatly to various measurements.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a digital inclination measuring device according to the present invention.

FIG. 2 is a circuit diagram of a bridge circuit of the servo-type tilt sensor in the embodiment.

FIG. 3 shows measurement data obtained by the bridge circuit.

FIG. 4 is a diagram showing an operation of the servo-type tilt sensor drawn by the measurement data.

FIG. 5 is a diagram showing an inclination angle-output characteristic of a servo type inclination sensor.

FIG. 6 is an explanatory diagram showing a conventional technique.

FIG. 7 is an explanatory diagram showing a conventional technique.

FIG. 8 is an explanatory diagram showing a conventional technique.

FIG. 9 is an explanatory diagram showing a conventional technique.

FIG. 10 is an explanatory diagram showing a conventional technique.

FIG. 11 is an explanatory diagram showing a conventional technique.

FIG. 12 is an explanatory diagram showing a conventional technique.

FIG. 13 is an explanatory diagram showing a conventional technique.

FIG. 14 is an explanatory diagram showing a conventional technique.

[Explanation of symbols]

1 Servo-type inclination sensor 2 Differential amplification circuit 3 LP filter circuit 4 Linearization circuit 5 Polarity inversion circuit 6 V-F conversion circuit 7 Frequency divider 8 Counter circuit group 9 Multiplexer 10 Decoder 11 Display circuit 12 Power transformer 13 Stable Circuit 14 Transmitter 15 Magnet 16 Yoke 17 Moving coil 18, 19 Shutter 20, 21 Reflective photoreflector 22 Bridge circuit L0 to L4 Load line Tra, Trd Phototransistor V _CE a, V _CE d of reflective photoreflector 20, 21 Tra-Trd collector-emitter voltage Ro, R1, R2 resistor VR variable resistor Vs power supply Va, Vd, Eo voltage Io output current Ia, Id phototransistor current O center of moving coil G center of gravity of moving coil

Claims (2)

[Claims] 1. A movable coil type instrument has a fixed portion fixed in a case, and a movable coil of the movable coil type instrument is rotatably supported in a pendulum shape by shifting a center of gravity of the movable coil by a span band to be movable. Reflecting plates are fixed to both sides of the coil in the direction perpendicular to the span band direction, and a pair of reflection type photoreflectors for emitting light toward the reflecting plate and detecting the distance from the reflecting plate by the reflected light are provided on the reflecting plate. The pair of reflective photoreflectors and the pair of reflective photoreflectors are fixed to each other and are fixed in the case.
A bridge circuit is formed by a plurality of resistors, the movable coil is connected to the center of the bridge circuit, and when the case is tilted, the imbalance of each output of the two reflection type photoreflectors is caused by the movable coil. Is a digital tilt measuring instrument comprising a servo-type tilt sensor in which torque is balanced by feeding back the current to the movable coil so that the movable coil follows the rotation of the case, wherein the bridge circuit of the servo-type tilt sensor is used. Connects a variable resistor between the two reflective photoreflectors,
A power supply is connected between the intermediate tap of the variable resistor and the connection point of the two resistors, and the voltage-current characteristic of each reflection type photoreflector is adjusted by adjusting the variable resistor. A digital inclination measuring instrument characterized in that an operating point of a load line drawn on a curve is stabilized so that zero change of the servo type inclination sensor is eliminated. 2. The digital tilt measuring instrument according to claim 1, wherein the variable resistor is replaced with two fixed resistors each having a resistance value on both sides of the adjusted center tap.