SENSORS USED IN WASHING MACHINE AND THEIR FUNCTIONING

SENSORS USED IN WASHING MACHINE AND THEIR FUNCTIONING

As the cam turns, it presses a spring against the cylinder, making it harder for the cylinder to pop up. This means that the water level will have to rise some more before the pressure in the hose will be high enough to trigger the switch.

TEMPERATURE SENSOR

WATER LEVEL CONTROL

Modern machines use thermistors as Temperature Sensors. Thermistors are low-cost temperature-sensitive resistors and are constructed of solid semiconductor materials which exhibit a positive or negative temperature coefficient.

The thermistor's high sensitivity (typically, –44,000 ppm/°C at 25°C allows it to detect minute variations in temperature which could not be observed with an RTD or thermocouple.

Its response time is very short due to its small size.

When there is mains supply the transistor Q1(BC558) will be OFF and the capacitor C1 will be charged. When the mains supply fails the transistor Q1 becomes ON and the capacitor C1 discharges through the Q1 to drive the buzzer to produce an alarm.

The capacitor C2 is the filter capacitor for the bridge. Diode D2 prevents the discharge of the C2 when mains fails. If D2 is not there,  the alarms will remain silent for a time capacitor C2 to fully discharge after the power failure.

AN INTODUCTION TO WASHING MACHINE

This switch controls how high the tub fills with water. The big end of the hose connects to the bottom of the tub, while the small end connects to the switch. As the water level in the tub rises, water rises in the hose also; but the air in the hose is trapped, so as the water rises, the air is compressed.

MAINS POWER FAILURE ALARM/DETECTOR

Washing machines are a common feature today in the Indian household.

The most important utility a customer can derive from a washing machine is that it saves the effort he/she had to put in brushing, agitating and washing the cloth.

LIST OF SENSORS EMPLOYED IN THE FUNCTIONING OF WASHING MACHINE

Temperature Sensor

Water Level Sensor

Dirt Sensor

Pin out of balance Detector

Leak Detector

Mains Failure Sensor

LEAK DETECTOR

Automatic Washing Machine Water Shutoff Valves with Leak Sensor are used in residential applications to protect against catastrophic water damage from a burst inlet hose connected to a washing machine in use or unattended. The signal is transmitted whether the washing machine is on or off, and then opens or closes the hot and cold inlet valves as needed to allow or prevent water from flowing to the washer. If it detects a leak, current flow to both the hot and cold water valves are immediately interrupted and closed.

Inside the housing of this switch is a little piston. The pressure in the hose pushes the piston up. When it is raised far enough, it pops up and closes an electrical contact. This set point, where the contact is lost, is adjustable, and in the picture you can see the cam mechanism that is connected to the adjuster knob on the control panel of the washer.

DETECTING OUT OF BALANCE CONDITION

A spectrum of methods is currently being used to detect out-of-balance conditions. At the low end is a combination of mechanical switches that sense when the drum displacement exceeds an established safety threshold. If excessive motion is generated, the drum itself will activate the switches and turn off the machine. A more sophisticated approach consists of monitoring variations in the machine’s electric motor torque, rotational velocity, or the amount of power drawn.

In a horizontal-axis machine (front loader), an unbalanced load will generate a gravity-induced torque or velocity ripple during each revolution. This condition can be detected by looking at the motor currents and/or voltages, or the rotational speed (tach) signal available on most washing machine motors. This signal is generally a pulse train whose frequency should be constant at steady speed. The signal is fed into the main control unit microcontroller and its frequency is monitored for any variation. A velocity ripple will reflect load imbalance.

In the presence of an unbalanced load, the tach signal generated by the motor of a front-loading clothes washer exhibits a ripple at a given rotational speed. The machine can be programmed to shut down or take corrective action if and when the ripple exceeds preset threshold levels symptomatic of an excessive out-of-balance condition that could lead to undesirable effects at higher spinning speeds.