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Probe: design
What is the function of a probe?
Temperature probes record the temperature of a medium and transmit it to the sensor. To do this, the probe material must first adjust to the ambient temperature. This is why the temperature of the medium is never measured directly — only the temperature of the probe or sensor is measured.
The probe requires a certain amount of time until it reaches equilibrium with the measured substance. A probe has adopted the temperature of the measured substance when its temperature is 99 % identical to the ambient temperature. This time is called the t99 time.
Temperature probes
Different designs for different applications.
Equalisation time depends on the medium and probe design.
Accurate measurement requires sufficient equalisation time (t99 time).
What probe designs are there?
Depending on the application, different probe designs are distinguished. Just as you would use a different knife to cut bread than to cut meat, there are different probes for temperature measurement.
Air probe
Impeded heat transfer between air and sensor.
Sensor is exposed; ideal for flowing air.
t99 ideally approx. 7 sec.
Surface probe
Large temperature jump, as air acts as an insulator.
Air insulation is overcome by using a contact thermometer.
t99 ideally approx. 3 sec.
Immersion thermometer
Immersion in liquids for temperature measurement.
Equalisation time is reduced by moving the probe.
t99 ideally approx. 0.5 sec.
Penetration probe
Penetration into solid or semi-solid media (e.g. food) for temperature measurement.
Direct contact with the medium ensures rapid equalisation.
t99 ideally approx. 0.5 sec.
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