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Temperature Monitor Schematic Circuit Diagram

Temperature Monitoring Systems in Various Industries

Temperature monitor systems have become indispensable tools in recent years, finding widespread application in healthcare, hospitals, clinics, the food industry, and various other sectors. These systems are designed to effectively regulate and control the temperature of specific environments, catering to the diverse needs of these industries.

Tailored for Small Spaces with Reliable Sensor

This temperature monitor is purpose-built for relatively compact spaces, such as living rooms. It employs a readily available LM335 sensor from National Semiconductor, providing an output voltage of 10 mV °C-1. This output voltage is then compared to two reference voltages using IC1a and IC1b, with one of the references set by P1 and the other by P2. The output of these comparators determines the operation of D2, D3, and D5.

Signaling Temperature Fluctuations

When the voltage generated by D1 falls below either of the reference potentials, the outputs of IC1a and IC1b remain low, resulting in the illumination of D2. However, as the ambient temperature increases, the output of D1 also rises proportionally. When the sensor output falls between the two reference levels, the output of IC1a turns high while IC1b remains low, causing D3 to light up, indicating that the critical temperature has been reached. This system effectively signals temperature fluctuations, helping maintain desired environmental conditions.

Temperature monitor Schematic diagram

Relay Activation and External Load Control

At higher temperatures, the output of IC1b goes high, causing D5 to illuminate, while the other LEDs turn off. Simultaneously, T1 is energized, activating the relay. The relay’s contact can then trigger an external load, such as a buzzer, providing a visible and audible indication of the elevated temperature condition.

Preventing Unintended Activation

Zener diode D4 plays a crucial role in preventing unintended activation of T1 when D3 lights up. This occurs because the output voltage of IC1b experiences a slight rise due to the current flowing through this IC. By incorporating D4, the circuit ensures the proper functioning of the temperature monitoring system.

Adjustable Temperature Thresholds

Users can set the temperature thresholds at which the LEDs should light using P1 and P2. However, it’s essential to note that the monitor is specifically designed for normal temperature ranges between 25 °C and 100 °C. Proper calibration ensures accurate temperature monitoring and appropriate response to temperature variations.

Current Consumption Considerations

The temperature monitor operates with a current draw of approximately 20 mA. When the relay is energized, the current consumption increases to around 50 mA. Being mindful of these current levels is crucial for efficient and reliable operation of the monitoring system.



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