JPS6165113A - Sensor circuit with zero point compensation - Google Patents

Abstract

PURPOSE:To compensate the drifting of a holding circuit by summing up a sensor signal output of a differential amplifier and a zero point corrector signal output, converting the summed output into a digital signal and storing the resulted signal at the correction of the zero point, then converting the digital signal into an analog to output the signal. CONSTITUTION:A detecting signal Vo through a detecting terminal 1 and a preamplifier 2 is inputted to one input terminal of the differential amplifier 3 and its output is extracted as a sensor output Vo' and also inputted to one input terminal of an adder 6. A zero point correcting value (e) is applied to the other input terminal of the amplifier 3 and the circuit 6. Conversion data from an A/D converter 7 which is obtained by converting and inputting the output of the circuit 6 are temporally stored in a latch circuit 8, the stored data are converted by a D/A converter 9 and outputted as the zero point correcting circuit (e) and the timing of the converters 7, 9 and the circuit 8 are controlled by a control circuit 10. Consequently, troubles due to the ordinary charging and storage of a capacitor can be removed.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a senna 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 physical signals of various detection targets such as photoelectric, displacement, and velocity signals into electrical signals. The transducer, which is the main part of this sensor, generally responds to physical displacement (for example, changes in light intensity or angle > t-
It is comprised of a detection end that performs K conversion of electrical displacement (for example, changes in current value or resistance value), and a preamplifier that amplifies the electrical displacement obtained at this detection end to a level that allows signal processing. Fig. 2 (A) shows the optical sensor converter together with its zero point correction circuit.The photodiode p serves as the detection end, and the current is proportional to the input light amount (DOQ~1m7k), and this current is transferred to the preamplifier PA. It is converted and amplified into a voltage signal (θ~10v). FIG. 2(B) shows an angle sensor variable/discharge B, in which a potentiometer PM is used as an angle detection end to extract a divided voltage, and this voltage is impedance-converted by a voltage follower 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 2 (A), a zero adjustment circuit consisting of a town 7S resistor VF and a voltage changing resistor R is provided, and the input light amount is set to zero during correction, and a variable resistor is used. There is one that improves the VFI so that the output voltage vo becomes zero.

Further, FIG. 3 shows a zero point correction circuit used in industrial processes and inspection processes. In this case, the output Ml of a sensor transformer consisting of a detection terminal and a preamplifier λ.

is set as one input of the differential amplifier 3, and the other input is set as the output VH of the hold circuit≠. Capture and store the entire preamplifier output when the output band at the end is set to zero, and use it as the output VFI of the hold circuit that is subtracted from the output of the tit preamplifier.

In this conventional example, zero correction can be done by simply operating the switcher that supplies the output of the preamplifier 2 to the input of the hold circuit Hiro during measurement, eliminating the troublesome work of adjusting the variable resistor in step 5 of Fig. 2 (A). Done? Problems to be Solved by the Invention The conventional zero point correction circuit shown in FIG. It is possible to perform zero point correction for the entire Senna converter including However, since the hold circuit ≠ uses the capacitor's charge memory, there is a drift due to natural discharge. This drift can be reduced by increasing the capacitance of the capacitor, but since the preamplifier output current is relatively small, the photovoltaic process takes time, making it difficult to press the switch, 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 multiplier whose sensor output is the difference between the output of a sensor transformer and a zero point correction signal, and an adder which takes the sum of the sensor output and the zero point correction signal. and a storage circuit that converts the output of the adder circuit into a digital signal during zero point correction, stores it, converts the content back into an analog signal, and outputs the converted signal as the zero point correction signal.

When the displacement of the force sensor converter is 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 in the differential amplifier, and the zero point correction value is added to the difference by the addition circuit. A drift component appears in , and by using this as a zero point correction value as the stored data of all the memory circuits, the output of the differential amplifier becomes zero excluding the drift component, and the zero point correction value is made to be the zero point correction value. 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.

Example FIG. 1 is a circuit diagram showing an embodiment of the present invention.

Detection signal Vo of physical quantity by detection terminal/and preamplifier λ
d difference excitation width amplifier is applied to one input. The output of the differential amplifier 3 is taken out as the senna output vol and is also applied to one addition input of the addition circuit B.

The zero point correction value e is given to the other input of the differential amplifier 3 and the adder circuit B. The output of the adder circuit B is input to the A/D converter 7. The latch circuit r takes in periodic test data of the A/D converter 7 for temporary storage. D
/ The A converter converts the data stored in the latch circuit r into an analog signal and outputs it as a zero point correction value. The control circuit IO generates the variable F'b7t and the variable timing and latch timing of the latch circuit r by turning on the zero point correction command switch 1OA.

In such a configuration, the memory circuit consisting of 7 to IO converts the output of the adder circuit B into a digital signal, stores it in the latch circuit t, and outputs the analog signal output corresponding to this stored data as the zero point plus value e. do. Then, the data stored in the latch circuit r is updated by temporarily turning on the switch IOA:
Then the control circuit 10 issues a conversion command to the A/D converter 7, and then the latch circuit? This is done by issuing a latch command to each one once. A periodic inspection command is also issued to the D/A converter 2 to output an analog signal (zero point correction value) for the data stored in the latch circuit r as a DC voltage.During zero point correction, the physical quantity input at the detection end is set to zero. do. For example, if it is an optical sensor, its optical input is cut off. In this state, before the switch 10 A t'' is turned on to update the data stored in the storage circuit, the relationship between the output vo of the preamplifier λ and the output vo' of the differential amplifier 3 is expressed by the following equation (1).

V6'=V(1-e+e d-111, (1) where 1 θd is the drift of the differential amplifier 3.

Next, when the switch 10Af is turned on, the stored data is updated to V6'+e, which is the output of the adder circuit B, and becomes the new zero point correction @eN.

LA N = Vo' + e -・" (2) Eliminating θ from both equations (1) and l(2) yields vo-θH+ e
a = 0-- (3). In other words, the updated zero point correction value θN is used to obtain the output vo'=of the differential amplifier 3.
o, detection end/, preamplifier and differential amplifier 3
This is the zero point correction that corrects each drift amount. This zero point correction value e is continuously applied to subsequent sensor operations, thereby eliminating drift in subsequent measurements. Moreover, e is an adder circuit IG
, A/D converter 7. 'f)/A converter conversion.

The t correction includes calculation errors, and data destruction does not occur in digital storage by the latch circuit r.

Effects of the Invention According to the present invention, since the zero point correction value is stored digitally, it takes 9 hours less time to change the stored contents and to update the memory (memory operation frequency) compared to the conventional analog quantity storage using the charging voltage of the 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, so that highly accurate correction can be obtained.

Brief explanation of the previous section Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 (A)
2(B) is a circuit diagram showing an example of a sensor converter, and FIG. 3 is a circuit diagram of a conventional zero point correction sensor.

l...detection end, λ...preamplifier, 3...differential amplifier, t...addition circuit, 7...A/D converter,
?・・・Latch circuit, ri...D/A converter, 10
...Control circuit, 10k...Switch for zero point correction command.

Figure 1

Claims (1)

[Claims] 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 differential sensor that uses the difference between the output of this converter and the zero point correction signal as the sensor output. an 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 during zero point correction and stored, and this content is returned to an analog signal and output as the zero point correction signal. 1. A zero point correction sensor circuit comprising: a memory circuit for storing data;