The hot water pipe from the water geyser of your bathroom may burst if it gets overheated and is left unattended. This circuit monitors the temperature of the water pipe. If the temperature of the pipe goes above certain limit, it flashes an LED.
The circuit uses a small sensor with inbuilt thermostat. It is actually an automatically resettable thermal switch that operates whenever its temperature exceeds the set limit. It is available in two versions, viz, normally open (N/O) and normally closed (N/C).
The N/O version closes the switch upon the set limit, while the N/C version opens the switch. The thermostat automatically resets as soon as the temperature returns to the initial state. It can be directly mounted on the part to be monitored.
The sensor is available in various temperature settings. The temperature limit is specific from 70°C up to 110°C for each model number. For instance, the type 67L080 will change state at around 80°C+5°C. You can select the type suitable for your requirement. Use a three-core wire for connecting switches to the relay.
The circuit uses very few components. Also, it does not require a separate power supply and can be connected to the power supply of the water heater suitably. Normally, the circuit remains idle and no current flows through it.
Three different types of circuits are described here. The circuit in Fig. 1 shows over-heating status of the pipe through LED1. As soon as the temperature of water pipe rises above the preset limit, the N/O contact of the thermostat closes and current flows through LED1. The LED1 glows to indicate that the temperature of the water pipe has exceeded.
The circuit in Fig. 2 gives aural indication of over-heated pipe through piezobuzzer PZ1. When the temperature of the pipe goes above the set limit, the N/O contact of the thermostat closes to sound the piezobuzzer.
The circuit in Fig. 3 gives audio-visual indication through piezobuzzer PZ2 and LED2. When the temperature of the pipe goes above the set limit, the N/O contact of the thermostat closes to light up LED2 and sound piezobuzzer PZ2.