JPS60239675A - Sensor circuit - Google Patents

Abstract

PURPOSE:To enhance the capacity of heat-cooking under all humidity environments, by enhancing sensitivity under low and high humidity conditions by forming a discharge circuit using a bidirectional non-linear element. CONSTITUTION:When voltage VIN is equal to a peak value VSS, voltages at both terminals of a bidirectional non-linear elements ZD1 become high even if the charge current of a condenser C1 is slight and voltage VOUT becomes also large. Because voltages at both terminals of the element ZD1 are constant even if the charge current becomes high and voltage VOUT is proportional to the reciprocal of sensor resistance RH, linearity is obtained and the sensitivity of a sensor circuit in a low humidity state is improved. Because the element ZD1 is bidirectional, the charged voltage of the capacitor C1 is discharged through the element ZD1. Then, constant at the time of discharging becomes almost equal to that at the time of charging and discharge is rapidly performed based on an extremely small value. Therefore, the charge applied to the capacitor C1, during the time when voltage VIN is equal to the peak value VSS, is discharged during the zero-volt period of voltage VIN. As a result, the sensor resistance RH (relative humidity) and the voltage VOUT show a linear characteristic and the sensor circuit shows good sensitivity even in low and high humidity regions.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit system for extracting an output signal from a sensor whose resistance value changes widely over a range of use.

Conventional configurations and their problems In recent years, household electrical appliances such as microwave ovens and air conditioners have become multi-functional and capable of complex control with the introduction of microcomputers (hereinafter referred to as "microcomputers"). For example, microwave ovens can now cook automatically by using sensors and microcomputers, allowing them to cook automatically by selecting a cooking menu and pressing the start button.

Accordingly, along with the development of sensors, importance has been placed on sensor peripheral circuits, particularly sensor signal capture circuits.

FIG. 1 is a diagram showing the humidity sensor characteristics, and represents the relationship between relative humidity and resistance. The usage range is relative humidity 0% to 100%, and the sensor resistance is 10 to 100%.
It varies by 10 Ω1. FIG. 2 shows a conventional signal acquisition circuit for a humidity sensor in a microwave oven. Here, C1 is a capacitor that prevents DC voltage from being applied to the sensor, R1 and R2 are resistors that determine the characteristics of the circuit, and Dl is a sensitivity switching diode.

Here, how to capture sensor signals will be explained.

An input signal vin as shown in FIG. 3 is applied to a terminal S (for example, an output port of a microcomputer) into which an alternating current signal for sensor signal detection is input, and an output signal V of the sensor terminal U is obtained.

It is configured to take out the ut. Now, the input signal vi
n is the period T0. Duty (Ton/T0)%, peak value v
When the pulse is ss, the output signal is V. ut is the period T.

The humidity level is taken in at the timing of TR and determined to be the humidity level vR. The sensor signal capture circuit will be explained using FIGS. 4 to 8. When the input signal vin=vss is 0, the charging current Ip from the input terminal S to the capacitor C1 is
Resistor R1 or diode D1. It flows through resistor R2. At this time, the voltage vin generated at the sensor end U is treated as an input signal. Further, when vss=Ov 0, the charge q accumulated in the capacitor C is discharged through the resistor R3, the resistor R1, and the sensor resistor R8. By forming such a charging/discharging circuit, no direct current voltage is applied to the sensor. By the way, as shown in FIG. 6, there is a relationship between relative humidity (or sensor resistance R) I) and sensor end output voltage vin. In other words, while the relative humidity changes by a certain amount, the output voltage vin does not change uniformly, but in a low humidity state of 20% or less or 7o%.
In the above-mentioned high humidity conditions, the amount of change is small and the sensitivity of the sensor circuit is poor. Low humidity condition (sensor resistance R
As shown in FIGS. 7 and 8, sensitivity switching occurs when the forward voltage of Dl) is large (when H is large), but as long as the sensor resistance RH is relatively large (up to point A in FIG. 6). , the current does not flow much, the voltage V across the diode is small, and the output voltage is V. The amount of change is also small.

In addition, in a high humidity state (when the sensor resistance RH is small), as shown in FIG. 10, when vin=vss 0,
When the charging current of capacitor c1 is large (that is, the time constant T, = CX(RM+R2) of the current when charging the capacitor becomes small), the voltage across 01(7) becomes large, and v
o. become. Still, V. In discharging at −〇v, the time constant T2 of discharging capacitor c1=, CX(R)I
+R1+R3) (here, R1>>R2) is large, the discharge current is small, and the charge Qp-C4·vo accumulated when charging the capacitor.

cannot be completely discharged, and the next cycle begins with a voltage Δv0° (=v0°-vop) being applied across both ends of the capacitor C1. Therefore, the output voltage V. ut also becomes lower by ΔV0/, making it impossible to obtain a normal voltage. Therefore, even in high humidity conditions, the sensitivity of the sensor circuit decreases. in this way,
The poor sensitivity of the sensor circuit in low-humidity and high-humidity conditions means that in actual cooking, more steam than is necessary must be generated, which often leads to overheating. Furthermore, it is extremely dangerous from a safety perspective due to abnormal temperature rise.

Purpose of the Invention The present invention solves the above-mentioned conventional problems by increasing the sensitivity of the sensor circuit at low humidity and high humidity.
The aim is to use an automatic heating device to maintain a constant level of cooking quality in all humidity environments, from low humidity to high humidity, and to ensure safety.

Structure of the Invention In order to achieve the above object, the sensor circuit of the present invention uses a bidirectional non-linear element to configure the discharge circuit in order to speed up the discharge of the DC current blocking capacitor.
By improving the low humidity and high humidity sensitivity, it has the effect of improving the cooking performance of the automatic heating device.

DESCRIPTION OF THE EMBODIMENTS FIG. 11 shows a circuit of the present invention. A resistor R2 connected in series with the bidirectional nonlinear element ZD1 is provided in parallel with the resistor R1 connected in series with the sensor R1. FIG. 2 shows the waveforms of the input signal vyLn and the output signal V.ut. Here, the bidirectional nonlinear element (for example, a constant voltage diode) has characteristics as shown in FIG. 13. That is,
For positive voltage application, if the voltage exceeds a certain voltage v0, no matter how much the current increases, the voltage V. becomes constant. Furthermore, whereas conventionally used diodes to which a negative voltage is applied do not allow current to flow at all, this bidirectional nonlinear element has a sufficient ability to conduct current. The circuit of the present invention will be explained using FIG. 14 and FIG. 16. vi
When n=vss, a charge current of C1 flows, but at this time, even with a small current I, the bidirectional nonlinear element ZD
As the voltage vZD1 across 1 becomes higher, the value of vout becomes larger.

In addition, even if the value of The sensitivity of the sensor circuit in low humidity conditions has been improved.In addition, in the discharge circuit of capacitor C1, the discharge time constant is T, = C,
R3) was large, but in the circuit of the present invention,
Since ZDl is bidirectional, discharge is possible throughout ZD1, and the discharge time constant is T,'-1=c,X(R
H + R2 + R5) - 〇, It is now possible to discharge. Therefore, vin-vss
The electric charge (Q0=C-Vo) charged across capacitor 01 during vin-Ov (time TOn) is
off+normal T. n (set as Toff), the output voltage at the sensor end U' becomes V
. ut has also become more accurate. Therefore, the sensor resistance (or relative humidity) and the output voltage V. As shown in FIG. 17, linearity can now be obtained in the relationship between ut and ut.

Therefore, the sensitivity of the sensor circuit in low humidity and high humidity conditions was improved.

Effect of the invention As described above, according to the present invention, the following effects are obtained.

(1) A simple configuration that uses a bidirectional nonlinear element (for example, a constant voltage diode) in the sensor circuit,
It was possible to improve the sensitivity of the #7 circuit in low humidity and high humidity conditions.

(The output voltage can be widened, the dynamic range is widened, and the noise resistance is improved.

(3) It is now possible to always flow a constant current through the sensor element and its circuit, eliminating the risk of poor contact due to coatings, etc.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram of the sensor, Fig. 2 is a conventional sensor circuit diagram, Fig. 3 is a conventional input/output timing chart, and Fig. 4 is a conventional sensor circuit diagram.
Figure 6 and Figure 6 are conventional charging/discharging circuit diagrams, Figure 6 is a characteristic diagram of conventional sensor resistance and output voltage, Figures 7 A, B, and 8.
Figures A and B are conventional charging circuit diagrams and timing charts, Figure 9 is a v-X characteristic diagram of diode D1, Figure 10 is a conventional sensor circuit input/output timing chart, and Figure 11 is
The figure is a sensor circuit diagram that is an embodiment of the present invention, Figure 12 is an input/output timing chart of the sensor circuit, and Figure 13 is a sensor circuit diagram.
The figure is an i-I characteristic diagram of the bidirectional nonlinear element, Figures 14 and 16 are charge/discharge circuit diagrams of the sensor circuit, Figure 16 is an input/output timing chart of the sensor circuit,
FIG. 7 is a sensor resistance-output voltage characteristic diagram of the same sensor circuit. R) I...Sensor, R1...Resistance, R
2...Resistance, ZDl...Bidirectional nonlinear element. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 2, 9 θV Figure 3 Figure 4 V Figure 5 Figure 6 Saimitsu Sensane/? s (ic-12) Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 13 Fig. 14 Fig. 16 Fig. 17 Insertion/? H

Claims (2)

[Claims] (1) comprising an AC power source for signal detection, a sensor having a large resistance value fluctuation range and nonlinear characteristics, and a bidirectional nonlinear element connected in series to the sensor, the bidirectional nonlinear element A sensor circuit that forms a discharge circuit. (2) The sensor circuit according to claim 1, wherein the bidirectional nonlinear element is formed by a parallel combination of a first resistor, a constant voltage diode, and a second resistor coupled in series.