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THERMOCOUPLES

NFPA TIE ROD PNEUMATIC

AND HYDRAULIC CYLINDERS

LINEAR VALVE ACTUATORS

RTD’S 101

RTD Advantages and Disadvantages


The major advantages that an RTD has over Thermocouples are: Stability, Precision, and Repeatability. The disadvantages are the price and response time. The following table explains in more detail.


Sensor Advantages Disadvantages
Thermocouple  Simple
 Inexpensive
 Large variety
 Large temperature range
 Rugged
 « Self-powered »
 Non linear
 Low voltage
 Require reference
 Less stable
RTD  More Stable
 More accurate
 More linear
 Expensive
 Current source required
 Small
 Self heating
 Small base resistance
Criteria Thermocouple RTD
Cost Low High
Temperature range Very large -450 à 4200 F Large -400 à 1200 F
Interchangeability Good Excellent
Long term Stability Fair Good
Accuracy Medium High
Sensibility (Output) Low Medium
Sensibility (tip) Excellent Fair
Response time Medium to fast Medium
Linearity Fair Good
Self heating None Low
Extension cable effect High Medium
Sensor dimension Very small to very large Small to medium


Stability is the ability of a sensor to measure temperature with precision for a given length of time.


Repeatability characteristics of a temperature sensor represents the ability of the sensor to keep the same physical behaviour for any give temperature even though it has been used and exposed to different temperatures. In other words, it’s ability to conserve it’s stability even after many heating and cooling cycles.


Precision and Tolerances (Compared to Thermocouples)


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