Probes: Design

What is a probe's job?

Temperature probes take on the temperature of a medium and transfer it to the sensor. To do this, the probe material must first adapt to the outside temperature. For this reason, it is never the temperature of the medium which is measured, but the temperature of the probe / sensor.

The probe requires a certain period of time to settle to the substance being measured. A probe has recognized the temperature of the substance being measured when its temperature is 99 % identical to the outside temperature. This period is known as the t99 period.

Which probe designs are there?

There are different probe designs depending on the application purpose. Just as one uses a different knife to cut bread than to cut meat, for example, there are different probes for temperature measurement.


Immersion/penetration probes

  • Acclimatization of the temperature of the probe and the liquid.
  • Reducing the acclimatization time by motion.
  • t99 ideally approx. 0.5 secs.
Temperature measuring instrument testo 915i

Air probes

  • Reduced heat transfer between air and sensor.
  • Sensor is free; good for air flow impact.
  • t99 ideally approx. 7 secs.

Surface probes

  • Large temperature jump, as air works as an insulator.
  • Cancellation of air insulation through contact thermometer.
  • t99 ideally approx. 3 secs.