RTD Calibrators
RTD Temperature Calibrators are used to troubleshoot and calibrate temperature probes and the instruments that are connected to the probes such as chart recorders, temperature controllers, and PLC's. Temperature is the most measured physical property so it is logical to invest in a calibrator.
Source Only vs. Read/Source Calibrators
Source
The minimum function of a calibrator is to source a known thermocouple and/or RTD. That permits performing zero/span adjustments. In source mode testing of conditions that otherwise would be difficult or unsafe is possible. Imagine testing a reactor high temperature alarm. With a temperature calibrator it is safe to simulate a 90% full condition to test a high alarm warning and 95% to test the high high (HH) alarm. Another example is simulating a zero and span to confirm that a remote temperature controller is reading correctly.
Read
For troubleshooting problems, reading the signal coming from the sensor is necessary.
How many RTD and Thermocouple types is enough in a Calibrator?
There are many different thermocouple and RTD types of temperature probes. Does that mean your new calibrator needs to be able to handle all of them? Maybe, if you are a contractor you might come across several. Facilities with wide temperature ranges and applications might need the capability too.
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Most Popular Temperature Probe Types |
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K T/C |
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J T/C |
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T T/C |
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PT-100 (0.00385 coefficient) RTD |
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PT-1000 (0.00385 coefficient) RTD |
Thermocouple and RTD Basics
Thermocouples (T/C’s) generate a linear millivolt (mV) signal with temperature. They are two dissimilar wires soldered at the tip. RTD’s use a resistance principle. They are a thin coiled wire, usually platinum, that varies in resistance (ohms) with temperature. Thermocouples have a wider operating temperature range and better resistance to vibration and shock than RTD’s, but RTD’s are much more accurate and repeatable. RTD’s are 4-10 times more expensive. Type K, J, T, N, and E are known as base metal thermocouples because they are made from common metals and R, S, and B are made from Noble metals.
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Thermocouple Types and Applications |
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Type |
Wire Types |
Selection Advice |
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K |
Chromel/Alumel |
Wide range. Inexpensive. Popular.
Better at above 1000 °F (538 °C) |
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J |
Iron/Constantan |
Wide range. Inexpensive. Popular. Keep away from atmospheres that oxidize the iron.
Shorter life above 1000 °F (538 °C) |
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T |
Copper/Constantan |
Typically best accuracy, especially at ambient and below freezing. But lowest max temp.
Popular in Pharmaceutical industry. |
|
N |
Nicrosil/Nisil |
For applications where Type K have shorter life.
Better accuracy than K or J but less popular |
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E |
Chromel/Constantan |
Highest mV output. Medium temp range |
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R |
Platinum/Platinum-13% Rhodium |
High temp industrial applications above 1000 °F (538 °C) |
|
S |
Platinum/Platinum-10% Rhodium |
High temp laboratory applications above 1000 °F (538 °C) |
|
B |
Platinum/30% Rhodium |
Same as type R and S but higher max temp
and lower mV output |
Notice in the above thermocouple table, absent is the temperature range and accuracy. They vary so much by manufacturer that it is best to look at the specifications when selecting a temperature probe.