Temperature Sensors and Applications

Thermocouple

• Versatile
• High span in one device
• Populatr in metallurgy and semiconductor processes

Resistance Temperature Detector (RTD)

• Precise
• Linear
• Stable
• Popular in pharmaceutical, biotechnology and chemical proceses

Thermistor (Sensors on a chip)

• small, easy to package
• used in phones and PCs

Infrared

• The only non-contact sensor
• Excellent for measuring temperature safely from a distance

Thermistors - characteristics:

• Most have a non-linear, negative temperature coefficient (NTC)
• The exact nonlinear curve or temperature versus resistance is highly material dependent.
• 25 degrees Celsius (Base resistance), mostly 2,252 Ohms ~ 10,000 Ohms
• Accuracies of +-0.1C ~ +-0.2C
• commonly used as overheating protection
• LCD's (to compensate display contrast)

NTC Temperatures vs Resistance Curve

| Steinhart Hart Equation

| Beta parameter equation

Resistance Temperature Detector (RTD)

• Traditionally, a coiled Platinum wire wrapped around a ceramic or glass core.
• Typically packaged inside a probe with a metal sheath
• Thin film RTD's consist of parallel traces deposited on a ceramic substrate
• Range of -200C ~ 800C
• No periodic calibration checks required
• Usuage for pharmaceutical and biotechnology plan
• RTD principle also used in gas flow sensors
• DIN/ICE 60751 is the global standard
• Temperature coefficient of resistance (TCR) of 0.00385 Ohm/C between 0 ~ 100 C

• Resistance Tolerance

  • Class A = +-(0.15 + 0.002 x T)C
  • Class B = +-(0.3 + 0.005 x T)C

• RTD vs. Thermistor Curves, PTC - Positive temperature coefficient thermistor

• RTD Linearization for Precise readings

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