JPH0229294A - Water level detecting device for washing machine - Google Patents

Abstract

PURPOSE:To prevent noise from entering into an oscillating circuit even though noise is introduced through a lead wire so as to prevent erroneous operation and detection, and to enhance the reliability of a washing machine by providing resistances in the oscillating circuit even though a resonant circuit is arranged separately from the oscillating circuit and both are connected together by lead wires. CONSTITUTION:Resistances 27, 28 are connected in series on the input side of an oscillating circuit 29 in order to inhibit noise. With this arrangement, noise is restrained from entering through a lead wire 31 so as to enable the noise level to be lowered. In this arrangement, the waveform of an input to an inverter 25 prevents large noise from being applied to the inverter 25, and accordingly, it is possible to aim at enhancing the reliability of the oscillating circuit 29. Further it is possible to prevent a water level detecting circuit 30 from erroneously operating due to a signal delivered to the same from the oscillating circuit 29.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a water level detection device for a washing machine that detects the water level in a tub of a washing machine.

2. Description of the Related Art Conventionally, water level detection devices for this type of washing machine have been used as shown in FIGS.
The configuration was as shown in the figure.

Figure 4 is a cross-sectional view of the main parts of the water level detection device, and 1 is a diaphragm that moves up and down due to pressure changes accompanying changes in the water level in the washing tub.A magnetic material 2 is attached on top of this diaphragm 1. . 3 is a coil placed around the magnetic body 20, and as the magnetic body 2 moves up and down together with the diaphragm 1, the inductance of the coil 3 changes;
Taking this change in inductance as an electrical signal,
This is intended to detect changes in the water level in the washing tub. Further, 4 is a spring that linearizes the change in inductance with respect to pressure, 6 is an adjustment screw, and e is an outer frame that houses the above-mentioned parts.

FIG. 6 is a circuit diagram for converting the change in inductance with respect to pressure explained in FIG. 4 into an electrical signal (frequency). In FIG. 6, 3 is the coil explained in FIG. 4, and the inductance changes depending on the pressure. 7 and 8 are capacitors, 9 is an inverter, and 10 is a resistor. Further, 11 is a capacitor for power supply noise countermeasure, and 12 is a water level detection circuit.

With this circuit, the coil 3, capacitors 8, and 8 form a resonant circuit, and the inverter 9, which serves as an oscillation circuit connected to this resonant circuit, sends the change in inductance as a change in oscillation frequency to the water level detection circuit 12, and outputs it as a water level. It is something to detect. That is, when the magnetic body 2 shown in FIG. 4 moves up and down due to pressure changes, the inductance of the coil 3 changes, the oscillation frequency of the oscillation circuit changes, and the frequency change is detected as a water level change.

In addition, Fig. 6 shows the mounting position of the water level detection device in the main body of the washing machine, where 13 is the pressure detection part, 1
4 is a water level detection unit with a built-in oscillation circuit including a resonance circuit and an inverter, 16 is a control circuit body with a built-in water level detection circuit 12, and a pressure hose 18 is connected between the pressure detection unit 13 and the water level detection unit 14. The water level detection section 14 and the control circuit main body 16 are connected by a lead wire 19.

Problems to be Solved and Attempted by the Invention In such a conventional configuration, since the lead wire 19 is routed and connected between the water level detection section 14 and the control circuit main body 16, it is difficult to open or close the power switch during operation. In this case, noise is induced in the lead wire, which is applied to the components of the water level detection circuit, causing false detection and malfunction.

In view of the above problems, it is an object of the present invention to improve the reliability of a water level detection device against such noise.

Means for Solving the Problems In order to achieve the above object, the water level detection device for a washing machine of the present invention includes a diaphragm that moves due to pressure accompanying changes in the water level in the washing tub, and a magnetic body attached to the diaphragm. and a coil whose inductance changes due to the movement of the magnetic material, a resonant circuit consisting of the coil and a capacitor, an oscillation circuit connected to the resonant circuit, and a microcomputer etc. that receives the oscillation signal of this oscillation circuit as input. The resonant circuit is separated from the oscillation circuit and the water level detection circuit, the resonant circuit and the oscillation circuit are connected via a lead wire, and a resistor is connected in series to the connection side of the oscillation circuit to the resonant circuit. It was constructed as follows.

Effect: With this configuration, the noise generated in the lead wire when the power switch is opened or closed is attenuated by the series-connected resistor of the oscillation circuit, and the noise is prevented from being directly applied to the water level detection circuit or the oscillation circuit itself. This can greatly improve reliability.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows the configuration of a water level detection device for a washing machine in this embodiment. In the figure, 21 is a coil whose inductance changes as the positive pressure changes. Capacitors 22 and 23 form a resonant circuit 24 together with the coil A/21, and these are installed at the position of the water level detection section 14 shown in FIG. 25 is an inverter, 26 is a feedback resistor, 27 and 28 are noise prevention resistors, and the inverter 26 and the resistors 26, 27, and 28 form an oscillation circuit 29. Further, 30 is a water level detection circuit using a microcomputer or the like, which receives the output of the oscillation circuit 29, converts the frequency change into a water level change, and detects the same. The oscillation circuit 29 and the water level detection circuit 30 are integrated and installed at the position of the control circuit main body 16 shown in FIG. 6, and are connected to the resonance circuit 24 by a lead wire 31.

FIG. 2 shows an example of an oscillation waveform of the oscillation circuit 29. That is, the waveform of the input section 32 of the inverter 26 is normally as shown in FIG. 2a. FIG. 3 shows the relationship between the pressure P in the washing tub (correlated with the water level) and the oscillation frequency F of the oscillation circuit 29.

According to the above configuration, by separating the oscillation circuit 29 from the resonance circuit 24 and mounting it integrally with the water level detection circuit 30, the mounting space for the resonance circuit 24 can be reduced, and semiconductor components such as the inverter 26 can also be mounted. Therefore, moisture-proofing treatment can also be omitted.

Next, to explain the operation of the circuit, there is a coil 21 whose inductance changes, a capacitor 22, and a 23° inverter 26.
Oscillation is performed in a loop formed by the and resistor 26, and oscillation is performed at a frequency F corresponding to the inductance of the coil 21, that is, the pressure P due to the water level in the washing tub, and the output is sent to the water level detection circuit 3o. . The waveform of the input 32 of the inverter 260 at this time normally becomes an oscillation waveform as shown in FIG. 2a. However, if the power switch is opened or closed while the washing machine is running, the noise caused by the current cutoff can be
Lead wire 3 connecting resonance circuit 24 and oscillation circuit 29
If it is induced by 1 and there is no countermeasure, as shown in Figure 2,
A large negative voltage may be generated and destroy the device.

Therefore, by inserting resistors 27 and 28 in series on the input side of the oscillation circuit 29 to prevent noise, the lead wire 3
In this case, the waveform of the input 32 of the inverter 26 becomes a waveform as shown in FIG. 2C, and a large 7' noise is applied to the inverter 25. This can be prevented, and the reliability of the oscillation circuit 29 can be improved, and it is also possible to prevent the water level detection circuit 3o from malfunctioning due to the signal sent from the oscillation circuit 29 to the water level detection circuit 3o.

Effects of the Invention As is clear from the above embodiments, according to the present invention, even if the resonant circuit and the oscillation circuit are separated and a lead wire is used to connect them, the resistance is provided in the oscillation circuit. Even if there is noise on the lead wire, it prevents noise from entering the oscillation circuit itself and malfunctions.

It is possible to prevent false detections and greatly improve the reliability of washing machine water level detection devices.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a water level detection device for a washing machine according to an embodiment of the present invention, and FIG. 2 is a diagram showing waveforms of essential parts of the same.
Figure 3 is a diagram showing the relationship between the pressure in the washing tub and the oscillation frequency, Figure 4 is a sectional view of the main part of a water level detection device that converts pressure into coil inductance, and Figure 6 is a conventional water level detection in a washing machine. FIG. 6 is a circuit diagram showing the configuration of the device, and a sectional view showing the mounting position of the water level detection device in the washing machine. 1...Diaphragm, 2...Magnetic material,
3.21... Coil, 22.23... Capacitor, 26... Inverter, 24...
・Resonance circuit, 29...Oscillation circuit, 30...
...Water level detection circuit, 2A, 28...Resistance. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (1)

[Claims] a diaphragm that moves due to pressure associated with changes in water level in the washing tub; a magnetic body attached to the diaphragm;
A water level consisting of a coil whose inductance changes due to the movement of the magnetic material, a resonant circuit consisting of the coil and a capacitor, an oscillation circuit connected to the resonant circuit, and a microcomputer etc. that receives the oscillation signal of this oscillation circuit as input. a detection circuit, the resonance circuit is separated from an oscillation circuit and a water level detection circuit, the resonance circuit and the oscillation circuit are connected by a lead wire, the oscillation circuit and the water level detection circuit are integrated, and the resonance circuit of the oscillation circuit is A washing machine water level detection device with a resistor connected in series to the circuit connection side.