Temperature sensor
The temperature sensor, known as probe, is divided into several groups and has different types. In air conditioning and refrigeration systems, the use of three groups of temperature sensor is more common:
• Negative Temperature Coefficient sensor or NTC
• Positive Temperature Coefficient sensor or PTC
• Pt1000 sensor
NTC temperature sensor
NTC sensor is a type of thermistors family and has a negative temperature coefficient. The NTC thermistor provides higher resistance at decreasing temperature. This group of temperature sensor is usually divided based on the amount of electrical resistance at 25°C, for example 10kΩ@25°C. NTC temperature sensor has high accuracy and reasonable price, but their operating range is from -50 to 150 degrees Celsius for standard type. In air conditioning and refrigeration applications, generally NTC sensor is used for measuring ambient temperature and fluids with temperature of less than 100 degree Celsius.
PTC temperature sensor
PTC sensor as a thermistor, has a positive temperature coefficient. The PTC sensor provides lower resistance at decreasing temperature. That is, as the temperature increases, the electrical resistance also increases too. PTC sensors also have high accuracy and reasonable price. The operating range of PTC temperature sensors is up to 150 degrees Celsius. PTC sensor is usually installed on lines to sense fluid with high temperature like compressor discharge line.
Pt1000 temperature sensor
Pt1000 temperature sensor is part of the family of resistance temperature detector (RTD). These types of temperature sensors have a higher price compared to NTC or PTC sensors cause of using precious metals such as platinum to make it. Pt1000 sensor has much accuracy and wider operation range rather than NTC or PTC types. Usually, PT1000 sensor is used in refrigeration cycle to measure superheat temperature on outlet of evaporator.
Temperature sensors are installed on the systems and connected to an electronic controller. In following pages there are useful information about this type of controller.
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