NTC Thermistor Measurements

When working with Thermistor Probes that will be immersed in water an error may occur and is often ignored. This error is known as the immersion stem effect.

Immersion Stem Effect

Is an error effect that occurs when a portion of the thermistor probe is at a temperature other than temperature of the sample. A simple method for determining stem effects is to slowly insert the probe further into a sample at approximately the test temperature while observing the thermistors change in resistance to determine when there’s no further change with further insertion. When no further change is observed, stem effect error is eliminated.

How To Eliminate Immersion Stem Effect

1) The immersion should be at least 10 times the diameter of the probe.
2) The sample volume should be no less than 1,000 times the mass of the thermistor.