JPH0648197B2 - Zero correction sensor circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sensor circuit having a zero correction function.

2. Description of the Related Art Generally, various sensors are used for measurement and control, which convert a physical quantity of a detection target in various forms such as a light quantity, a displacement, and a speed into an electric signal. The transducer, which is the main part of this sensor, generally includes a detection end that converts a physical displacement (for example, a change in light amount or angle) into an electrical displacement (for example, a change in current value or resistance value), and this detection end. And a preamplifier that amplifies the obtained electrical displacement to a level capable of signal processing. FIG. 2 (A) shows an optical sensor converter together with its zero-point correction circuit. A photodiode PD as a detection end obtains a current (DCO ~ 1 mA) proportional to the amount of input light, and this current is supplied to a preamplifier PA as a voltage signal ( It is converted to 0-10V) and amplified. Fig. 2
(B) shows an angle sensor converter, potentiometer PM
Is taken out as a divided voltage as an angle detecting end, and this voltage is impedance-converted by a voltage follower VF.

In these sensor converters, in particular, 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 it is arranged and changes over time in the detection end itself. As shown in FIG. 2 (A), this zero drift compensation is provided with a zero adjustment circuit composed of a variable resistor VR and a current conversion resistor R ₁ to adjust the variable resistor VR by setting the input light quantity to zero during correction. and output voltage V _o is there are things to be zero.

Further, FIG. 3 shows a zero point correction circuit used in an industrial process or an inspection process. In this case, the output V _o of the sensor converter composed of the detection terminal 1 and the preamplifier 2 is used as one input of the differential amplifier 3, and the other input is used as the output V _H of the hold circuit 4 and the output V 0 whose difference is zero-compensated. _o '. Here, the hold circuit 4 takes in and stores the output of the preamplifier 2 when the physical quantity of the detection end 1 is set to zero, and thereafter, the output of the hold circuit 4 is subtracted from the output of the preamplifier 2 to obtain the output V _H.

In this conventional example, the zero correction does not require the troublesome work of adjusting the variable resistance as shown in FIG. 2 (A), and the simple operation of the switch 5 which gives the output of the preamplifier 2 to the input of the hold circuit 4 at the time of measurement is sufficient. It is often used in industrial processes and inspection processes that require frequent zero correction.

Problems to be Solved by the Invention The conventional zero point correction circuit shown in FIG. 3 is simple in correction operation and can perform zero point correction of the entire sensor converter including the detection end and the preamplifier. However, there is a zero drift in the differential amplifier 3 at the final stage, and this drift amount cannot be corrected.

In order to solve this problem, as shown in FIG. 4, it is realized by providing a feedback back system by the servo amplifier 6 which makes the value held by the hold circuit 4 such that the output of the differential amplifier 3 becomes zero. To be done. In this case, the servo amplifier 6 has a complicated circuit configuration including an integrating circuit and an adding circuit as constituent elements, and there is a problem that the sensor circuit becomes large and expensive.

Means for Solving the Problems According to the present invention, the output of a sensor converter and a zero correction signal are in positive phase,
A differential amplifier having an operational amplifier configuration that uses the difference between the two inputs as a negative-phase input as a sensor output, and holds one input terminal voltage of the operational amplifier at the time of zero point correction, and holds the voltage at the same amplification degree as the differential amplifier. And a hold circuit for amplifying and outputting as a zero point correction signal.

Drift appears in the output of the sensor converter when the displacement of the input physical quantity of the working sensor converter is zero, and the difference from the zero correction value is taken out by the differential amplifier as the sensor output. It At this time, the voltage at the inverting input terminal or the non-inverting input terminal of the operational amplifier of the differential amplifier is at a value divided by the amplification degree of the amplifier, and the amplification degree of the hold circuit that holds this value is Since the amplification factor is the same as the amplification factor, the zero-point correction value that is the output thereof matches the drift amount, and the output of the differential amplifier is set to zero excluding the drift amount, and the zero-point correction value is set to the drift amount. Then, the zero point correction including the drift amount of the differential amplifier is performed.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The physical quantity detection signal V _{o from the} detection end 1 and the preamplifier 2 is input to the differential amplifier 7 in the positive phase. The differential amplifier 7 is configured to have an amplification degree of 2 by the operational resistance R having the same value as that of the operational amplifier OA _1, and the zero point correction value e _H is input to the antiphase input to obtain the sensor output V _o ′. Further, the voltage V _{A at} the inverting input terminal of the operational amplifier OA ₁ is taken out to one end of the zero point correction command switch 8. The switch 8 is turned on at the time of zero correction, and supplies the voltage V _A to the hold circuit 9 as a hold input. The hold circuit 9 holds the input voltage V _A in the capacitor C as a charging voltage, and uses a non-inverting amplifier circuit composed of the operational amplifier OA ₂ and the two same resistors R to multiply the capacitor voltage V _c in phase with double amplification. Output as zero point correction value e _H.

In such a configuration, the input of the physical quantity at the detection end 1 is set to zero when the zero point is corrected. For example, in the case of an optical sensor, the optical input is turned on or off. Before turning on the switch 8 in this state, the voltage 2 × V _{c, which} is twice the voltage V _c of the capacitor C, becomes the zero correction value e _H , and the output V _o ′ of the differential amplifier 7 is V _o ′ = V. _o -e _H + e _d ......... is (1). Here, e _d is the drift amount of the differential amplifier 7. Next, when the switch 8 is turned on, the voltage V _{c of the} capacitor C is charged to V _A. At this time, the zero-point correction value e _H becomes e _H = 2V _c = 2V _A (2) including the drift e _d , and the output V _o ′ of the differential amplifier 7 is V _o ′ = V _o −e _{H + e d = V o -2V} a ...... becomes (3). Here, since the potential difference between the inverting input terminal and the non-inverting input terminal of the operational amplifier OA ₁ is almost zero, the voltage V _A is equal to V _A = V _o / 2 (4).

Therefore, when the zero point is corrected, V _o ′ = 0 (5), the output V _o ′ of the differential amplifier 7 becomes zero, and the drifts of the detection end 1, the preamplifier 2 and the differential amplifier 7 are corrected. It becomes the zero correction. This zero-point correction value e _H is continuously given to the subsequent sensor operation, and the drift amount is eliminated in the subsequent measurement.

EFFECTS OF THE INVENTION According to the present invention, the zero point correction value holds the input terminal voltage of one of the operational amplifiers constituting the differential amplifier, and the voltage is made equal to the amplification degree of the differential amplifier to obtain the zero point correction value. Therefore, the zero point correction value is obtained based on the value in which the output of the differential amplifier is reflected, and the zero point can be corrected together with the drift of the converter including the zero drift amount of the differential amplifier itself. Moreover, in terms of configuration, a simple and compact configuration that does not require the conventional servo amplifier can be realized with only a hold circuit and a switch.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2 (A) and 2 (B) are circuit diagrams illustrating a sensor converter, and FIGS. 3 and 4 are conventional zero point corrections. It is a sensor circuit diagram. 1 ... Detection end, 2 ... Preamplifier, 7 ... Differential amplifier,
8: Zero correction command switch, 9: Hold circuit,
OA ₁ , OA ₂ ... Operational amplifier.

Claims (1)

[Claims] 1. A sensor converter for converting a physical quantity to be detected into an electric signal at a detection end and amplifying this signal to a level at which a signal can be processed by a preamplifier, and an output of this converter and a zero-point correction signal are in positive phase and reverse phase. A differential amplifier having an operational amplifier configuration that uses the difference between the two inputs as a phase input as a sensor output, and holds one input terminal voltage of the operational amplifier during zero correction and amplifies the voltage with the same amplification degree as the differential amplifier. And a hold circuit for outputting the zero point correction signal as the zero point correction signal.