Page 24 of 49
TTI-22 Iss.04– 11/15
We recommend this display type for high-precision temperature measurements.
5 R1/RREF, R2/RREF
Display of the ratios of sensor resistance to internal reference resistance.
6 R1/R2, R2/R1
Display of the ratios of one sensor resistance to the other.
7.7
Performing a Self-heating Test
The term self-heating relates to the sensor being heated by the measuring current. The measured
temperature is therefore a bit higher than the temperature of the sample medium. Errors through self-
heating of approx. 2mK and higher can be determined with the self-heating test.
Temperature changes of less than 0.5mK at operations with the lower measuring current are within TTI-
22’s measuring uncertainty and cannot be interpreted as self-heating.
Usually the self-heating of the sensor is considered in the calibration parameters. If the measuring current
during calibration strongly deviates from the measuring current in TTI-22, or the thermal resistance (air,
water, still or moving) strongly differs, this function is useful for avoiding major errors. The self-heating of
sensors that are supposed to measure the temperature of still air, for example, is mostly already too
significant to be ignored.
1.
For the display select the temperature statistics (1 Sel. Display & Start > 4 Temperature Stat.).
2.
Set N>20 and note the average temperature TempI.
3.
Use the digit key <5> in the main menu to set Self.Heat.Test to On.
Now the measuring current is reduced times.
The lower right part of the display shows "SHT" for "Self Heating Test On"
4.
Go back to the temperature statistics menu.
5.
Note the average temperature TempI/÷2 and calculate the temperature difference (TempI -
TempI/÷2).
6.
Multiplying the determined temperature change by "2" gives you the current self-heating of the
sensor.
7.
For the actual measurement switch back to Self.Heat.Test: Off.
