Calorimeters are heat-measuring instruments. They form the basis of the vast majority of primary standards for rf and microwave power and, in addition, some types also find use as secondary standards. One problem which all have in common is the conflict between accuracy on the one hand and convenience factors such as adequate sensitivity and rapid response on the other hand. The main reason for this conflict is the limited range of thermal resistances of available materials, which forces compromises on the designer. The result is that calorimeters intended for use as primary standards tend to have long time constants, typically in the range 1 to 10 minutes, and are often very bulky, whilst commercially made secondary instruments have unknown errors which are difficult to evaluate without calibration against a more accurate instrument. Some calorimeter designs have succeeded in narrowing the gap between the two types, but this gap is still considerable. In the past it was common to find calorimetric power meters used as everyday instruments on the bench, but for most routine purposes the preference today is for the speed and sensitivity obtainable from thermistors, thermoelectric and diode power meters. Consequently for non-standards work the calorimeter has tended to be displaced by these instruments, in spite of its potentially high accuracy and stability of calibration.

Chapter Contents:

• 2.1 Commonly used calorimeter types
• 2.2 Some other calorimeter types
• 2.3 References

Inspec keywords: calorimeters; power meters; sensitivity; calibration; thermistors; heat measurement

Other keywords: calibration stability; diode power meter; thermistor; microwave power; rf power; calorimeter design; secondary standard; heat measuring instrument; thermal resistance; thermoelectric power meter; secondary instrument; calorimetric power meter

Subjects: Calorimetry