JPH0572525B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sensor circuit having a zero point correction function.

2. Description of the Related Art In general, various sensors are used for measurement and control, which convert various physical quantities to be detected, such as light intensity, displacement, and speed, into electrical signals. The converter, which is the main part of this sensor, generally has a detection end that converts physical displacement (for example, changes in light intensity or angle) into electrical displacement (for example, changes in current value or resistance value), and this detection end. It consists of a pre-amplifier that amplifies the electrical displacement obtained in the process to a level that can be processed as a signal. Second
Figure A shows the optical sensor converter together with its zero point correction circuit. A photodiode PD serves as the detection end to obtain a current (DC 0 to 1 mA) proportional to the amount of input light, and this current is converted to a voltage signal (0 to 10 V) by the pre-amplifier PA.
Convert and amplify. Figure 2B shows the angle sensor converter, which extracts a divided voltage using the potentiometer PM as the angle detection end, and outputs this voltage as a voltage booster.
Convert impedance with VF.

In these sensor converters, there is a considerable amount of change in the zero point, so-called zero drift, due to changes in the environment (temperature, humidity, etc.) in which the sensor converter is placed, aging of the detection end itself, etc., especially at the detection end. For this zero drift compensation, as shown in Figure 2A, a variable resistor VR is used.
A zero adjustment circuit is provided using a current conversion resistor _R1 and a variable resistor VR to set the input light amount to zero during correction.
There is a device that adjusts the output voltage V ₀ to zero.

Further, FIG. 3 shows a zero point correction circuit used in industrial processes and inspection processes. In this case, the output of the sensor converter consisting of the detection end 1 and pre-amplifier 2
V ₀ is set as one input of the differential amplifier 3, and the output V _H of the hold circuit 4 is set as the other input so that the difference can be outputted as an output V ₀ ' with zero compensation.
Here, the hold circuit 4 captures and stores the output of the pre-amplifier 2 when the physical quantity at the detection end 1 is set to zero, and thereafter uses it as the output V _H of the hold circuit 4 which is subtracted from the output of the pre-amplifier 2.

In this conventional example, the zero correction does not require the troublesome work of adjusting the variable resistor as shown in FIG. It is often used in industrial processes and inspection processes that require frequent corrections.

Problems to be Solved by the Invention The conventional zero point correction circuit shown in FIG. 3 has a simple correction operation and can perform zero point correction of the entire sensor converter including the detection end and pre-amplifier. However, since the hold circuit 4 uses the charge memory of the capacitor,
There is drift due to spontaneous discharge. This drift can be reduced by increasing the capacitance of the capacitor, but since the output current of the pre-amplifier is relatively small, it takes time to charge it, and the switch 5
This increases the time it takes to press , making quick measurements difficult. Further, since the drift of the differential amplifier 3, which is the final stage, cannot be compensated for, there is still a problem that the drift remains.

Means for Solving the Problems The present invention provides: a differential amplifier whose sensor output is the difference between the output of a sensor converter and a zero point correction signal; an adder circuit which takes the sum of the sensor output and the zero point correction signal;
A storage circuit is provided which converts the output of the adder circuit into a digital signal at the time of zero point correction, stores it, converts the content back into an analog signal, and outputs the converted signal as the zero point correction signal.

Operation When the displacement of the input physical quantity of the sensor converter is set to zero, a drift component appears in the output of the sensor converter, and the difference between this drift component and the zero point correction value of the memory circuit is obtained by the differential amplifier and the corresponding value is calculated. By adding the zero point correction value to the difference in the adder circuit, a drift amount appears in the adder circuit, and by using this as the zero point correction value as new stored data in the memory circuit, the drift amount is removed from the output of the differential amplifier. The value is set to zero, and the zero point correction value is set to the amount of the drift. Then, the zero point correction is performed including the drift of each element such as the differential amplifier, and the storage circuit holds the stored data without being destroyed until the next correction.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The detection signal V ₀ of the physical quantity from the detection end 1 and the pre-amplifier 2 is input to one side of the differential amplifier 3 .
The output of the differential amplifier 3 is taken out as the sensor output V ₀ ' and is also applied to one addition input of the addition circuit 6. A zero point correction value e is given to the other input of the differential amplifier 3 and the adder circuit 6. The output of the adder circuit 6 is used as a conversion input of an A/D converter 7. The latch circuit 8 takes in the conversion data of the A/D converter 7 for temporary storage. The D/A converter 9 is connected to the Latch corridor 8.
The stored data is converted into an analog signal and output as a zero point correction value. A control circuit 10 controls the conversion timing and latch timing of the converters 7 and 9 and the latch circuit 8 by using a switch 10 for commanding zero point correction.
It occurs when A is input.

In this configuration, the memory circuit 7 to 10 converts the output of the adder circuit 6 into a digital signal and stores it in the latch circuit 8, and outputs an analog signal output corresponding to this stored data as a zero point correction value e. The data stored in the latch circuit 8 is updated by temporarily turning on the switch 10A so that the control circuit 10 issues a conversion command to the A/D converter 7 and then a latch command to the latch circuit 8 once. A conversion command is also issued to the D/A converter 9 to output an analog signal (zero point correction value) corresponding to the data stored in the latch circuit 8 as a DC voltage.

At the time of zero point correction, the physical quantity input at the detection end 1 is set to zero. For example, if it is an optical sensor, it will cut off its optical input. In this state, before the switch 10A is turned on to update the data stored in the storage circuit, the relationship between the output V ₀ of the preamplifier 2 and the output V ₀ ' of the differential amplifier 3 is expressed by the following equation (1).

V ₀ ′=V ₀ −e+ed (1) Here, _ed is the drift of the differential amplifier 3. Next, when the switch 10A is turned on, the stored data is updated to V ₀ '+e, which is the output of the adder circuit 6, and becomes the new zero point correction value e _N.

e _N =V ₀ '+e...(2) If e is deleted from both equations (1) and (2), V ₀ -e _N +ed=0...(3). That is, the output V ₀ ' of the differential amplifier 3 becomes 0 due to the updated zero point correction value e _N , and the zero point correction is obtained by correcting the respective drifts of the detection end 1, the pre-amplifier 2, and the differential amplifier 3. This zero point correction value e
is applied continuously to subsequent sensor operations to eliminate drift in subsequent measurements. Furthermore, e is the conversion of the adder circuit 6, A/D converter 7, and D/A converter 9,
The correction includes the calculation error, and the latch circuit 8
Data corruption does not occur with digital storage.

Effects of the Invention According to the present invention, since the zero point correction value is stored and held as a digital quantity, it is possible to reduce the change in memory contents, the effort (memory operation frequency), and the time required to update the memory, compared to the conventional analog quantity storage using the charging voltage of a capacitor. problem is solved. In addition, since the zero point correction value has a feedback system from the output end, the correction value includes the drift of the differential amplifier and the drift of each part of the memory circuit, making it possible to obtain highly accurate correction.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
Figures A and 2B are circuit diagrams illustrating a sensor converter, and Figure 3 is a circuit diagram of a conventional zero point correction sensor. 1...Detection end, 2...Brieamp, 3...Differential amplifier, 6...Addition circuit, 7...A/D converter, 8...Latch circuit, 9...D/A converter, 10...Control circuit, 10A...Zero point correction Command switch.

Claims (1)

[Claims] 1. A sensor converter that converts the physical quantity to be detected into an electrical signal at the detection end and amplifies this signal to a level that can be processed by a preamplifier, and a sensor output that is the difference between the output of this converter and the zero point correction signal. a dynamic amplifier, an adder circuit that sums the sensor output and the zero point correction signal, and the output of this adder circuit is converted into a digital signal and stored during zero point correction, and this content is returned to an analog signal to be used as the zero point correction signal. A zero point correction sensor circuit comprising: a memory circuit for outputting data;