Silicon temperature sensor working principle

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Diodes are highly sensitive and linear temperature sensors. Silicone and germanium diode temperature elements are available from − 458 to 395 ° F ( − 272 to 202 ° C). They are accurate to 0.2 ° F (0.1 ° C) for temperatures that are above ambient and to 0.2% of their full scale range below that.Figure 4.7c depicts the diode-based thermometer circuits o fa silicone diode with a 1 mA constant current source, and Figure shows the circuits of a germanium diode with a6-V power supply.

The current through the silicon diode thermometer read-out could be anywhere from 10 µ A to 10 mA, but because higher currents result in higher errors due to self-heating, the currents are usually kept between 100 and 500 µ A. The meters used with germanium diodes usually have a range of0 to 50 µ A. Because of the low source impedances, a simple microampere indicating meter can be used.

This sensor can also be used to detect small temperature differences. The main advantages of the diode-type sensors are their high accuracy, particularly at cryogenic temperatures; small size; low cost; and good linearity The diodes are small enough for most applications, but where sensor size is a problem, micro diodes can be used. One of the disadvantages is that the variations between diodes require a calibration procedure for absolute accuracy, which also increases their costs.



Applications: –

Because of their low accuracy, integrated circuitry sensors are used in heating, ventilation, and air conditioning (HVAC) type services and to detect hot or cold spots in piping. IC sensors are most often used in near-ambient temperature measurement; germanium diodes are often used in extreme cryogenic applications, and silicon diodes are used from − 60 to 300 ° F ( − 51 to 149 ° C).

Ranges:-

Integrated circuitry sensors, from − 65 to 300 ° F ( − 54 to 149 ° C); silicon diodes, from − 60 to 300 ° F ( − 51 to 149 ° C); germanium diodes, from − 420 to 110 ° F ( − 251 to 43 ° C).Some diodes can cover the range of 1.4 to 475 ° F ( − 271.8 to 202 ° C).

Price:

The basic integrated circuitry transistor elements can cost less than $10. Uncalibrated diode sensor costs range from $75 to $400; calibration can cost an additional $200to $300. A calibrated diode with packaging and mounting for cryogenic service costs$600. Indicating monitor readouts for diode elements cost about $800.

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