A tiny 5-hole compound probe with NTC-thermister has been developed by the authors for measurement of flow parameters in the compressor. All problems encountered for the thermister to be used in measuring the flow temperature are discussed. The techniques for enlarging the temperature range measured are also considered

such as how to sift out the best thermister

how to apply a highly precise and voltage-stabilizing supply to an unbalanced bridge for transmitting an accurate millivolt signal

and how to set a limit to the self-heating power of the thermister. As a result

the temperature range is extended from 273K to 473K. The probe was tested in a single-stage compressor rig

and its function and performance were verified favorably.