JPS61193953A - Raindrop detector - Google Patents

Abstract

PURPOSE:To keep the extent of detection sensitivity constant, by installing such an amplifier that raises an amplification degree with reduction in the varied portion of impedance between electrodes of a raindrop detection. CONSTITUTION:When raindrops stick to the electrode 2 set up in a position where raindrops on the surface of an automobile are stuck, an ohmic value between pectinations of the electrode go down to some extent, and each time raindrops are stuck to, output voltage Vo of an operational amplifier A1 increases by degrees. Therefore a raindrop detector will not response to such raindrops as being left sticking on the electrode intact and producing no resistance variation. And that it responses to new raindrops at the same sensitivity in spite of the number of raindrops already stuck, and generates a detection signal.

Description

[Detailed Description of the Invention] [Summary of the Invention] The present invention provides a raindrop detector that includes electrodes exposed to rain and detects changes in impedance between the electrodes. In order to compensate for the correspondence, an amplifier with predetermined amplification characteristics is provided.

C. Industrial Application Field] The present invention relates to a raindrop detector equipped with electrodes from which impedance can be extracted in order to detect rainfall, and is suitable for use as a detector for an automatic wiper operating device of an automobile. It is something.

[Conventional technology]

2. Description of the Related Art Raindrop detectors are known that include electrodes and detect a decrease in resistance between the electrodes due to adhesion of raindrops.

[Problem that the invention seeks to solve]

In a known electrode-type raindrop detector, if the resistance when a raindrop of a certain diameter adheres is Ro, then the resistance between the electrodes when N raindrops of the same diameter adhere to the electrode is Ro / N. . Therefore, the change in resistance between the electrodes due to the number of raindrops is -Ro
/N2, and as the number of raindrops adhering to the electrode increases, the amount of change in resistance due to the next raindrop falling on the electrode decreases, resulting in a problem that the sensitivity decreases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a raindrop detector that solves the above-mentioned problems.

[Means for solving problems]

The present invention is characterized in that a raindrop detector that detects a change in inter-electrode impedance includes an amplifier that increases the amplification as the change in inter-electrode impedance decreases.

[Effect]

According to the present invention, regardless of the number of raindrops that have already adhered between the electrodes, a predetermined variation range appears in the amplified output each time a new raindrop adheres. Therefore, detection sensitivity can be kept constant regardless of the number of raindrops adhering between the electrodes.

〔Example〕

In the embodiment described below, an operational amplifier is connected to a detection bridge to constitute a resistance-voltage conversion circuit, and this operational amplifier is configured to have predetermined amplification characteristics.

In the electrical circuit of the raindrop detector shown in Figure 1, when raindrops adhere to the electrode 2 placed on the surface of the car where raindrops adhere, the resistance value between the comb teeth of the electrode decreases each time a raindrop adheres. Operational amplifier A.

The amplified output voltage ■0 increases in a stepwise manner. The resistor R4 is inserted as a resistor for circuit stabilization because the resistance value between the electrodes 2 becomes approximately infinite when no raindrops adhere to the electrodes 2. The capacitor C2 has an integral function and removes noise induced into the electrode 2. The stepwise increasing voltage ■0 is taken out through a differentiating circuit of resistors and capacitors C, R2, and the voltage change ■2 is extracted and amplified by an operational amplifier A2, which is then input to an operational amplifier A3 used as a comparator. to go into. Therefore, the detection output voltage
, is output as a pulse signal.

Figure 2 shows the wiper automatic control device. In FIG. 2, the raindrop detector 3 is the same as that shown in FIG. 1, and when the ignition switch 9 is turned on, power is supplied to the system. The ground terminal of the raindrop detector 3 is connected to the terminal C2 of the wiper controller 4, and the wiper switch 5 is set to the intermittent position I.
Since C1 is grounded only when operated to NT, the raindrop detector 3 is operable only when the wiper switch 5 is in the intermittent position INT.

If the resistance between the electrodes when one raindrop of a certain diameter adheres to the electrode 2 is Ro, then the resistance between the electrodes 2 when N raindrops of the same diameter as the electrode 2 adheres is R.

is equivalent to a resistance connected between N electrodes, and Ro
/ N. Therefore, the resistance change when the Nth raindrop adheres to the electrode 2 is -Ro/N(N-1), and it can be seen that as the number of raindrops increases, the resistance change becomes smaller. This is shown in FIG.

The resistance Ro of a raindrop with a diameter of 1 in the circuit shown in Figure 1
The output voltage Vo when a substance adheres to the N-thin electrode 2 is V
o (N)=VI' (R3/ (RO/N)+1
). In this case, the output voltage change with respect to the number of raindrops is Vo (N)' = V+ ·R3/Ro, and a constant voltage change can be obtained regardless of the number of raindrops. This is shown in the graph of FIG. From the above, the first
The circuit shown in the figure can be said to be a linearization circuit that converts a resistance change that decreases due to an increase in the number of raindrops adhering to the electrode 2 into a constant voltage change regardless of the number of raindrops. Furthermore, since one end of the electrode 2 is grounded, this circuit is resistant to external induction. The amount of change in the output voltage can be extracted using the differentiating circuits C, R, etc. in FIG.

Thus, the raindrop detector 3 generates a pulsed output signal in response to newly deposited raindrops on the electrode, and the wiper controller 4 drives the wiper motor 6 in response.

In this case, the raindrop detector 3 does not respond to raindrops that remain attached to the electrode and do not cause a change in resistance, and does not respond to new raindrops with the same sensitivity without increasing the number of already attached raindrops. Since the detection signal is generated, the operating density of the wiper motor 6 can be made to correspond accurately to the rain condition.

In the circuit shown in FIG. 1 of the above-described embodiment, a resistor R4 was connected in parallel with the electrode 2 for circuit stabilization, but even if this resistor R4 is removed, the basic function will not be impaired.

The output stage of the raindrop detector 3 is equipped with a comparator (A
By interposing a counter that counts the detection signal output from 3), a drive output signal can be given to the wiper controller every time the count of the counter reaches a certain number.

[Brief explanation of drawings]

Fig. 1 is an electrical wiring diagram of an embodiment of the raindrop detector according to the present invention, Fig. 2 is an electrical wiring diagram of an automatic wiper control device using the raindrop detector shown in Fig. 1, and Figs. 3 and 4. 2 is an explanatory diagram of the operation of the raindrop detector shown in FIG. 1. FIG. 2... Electrode, 3... Raindrop detector, A1... Operational amplifier, R1, Rz, Rs... Resistance, C+, Rs...
・Capacitors and resistors that make up the differential circuit. Representative Patent Attorney Takashi Okabe Figure 1 Figure 2

Claims (1)

[Claims] A raindrop detector comprising electrodes exposed to rain and detecting changes in impedance between the electrodes, the raindrop detector comprising an amplifier that increases amplification as the impedance between the electrodes decreases.