Page 44 of 49
TTI-22 Iss.04– 11/15
If the additional systematic deviation throughout the entire measuring range is supposed to be smaller than
1mK, the change of the reference resistance can amount to a maximum of 1ppm. The internal reference
resistor has to be calibrated every two months.
In case of a limited measuring range or a lower accuracy requirement, the calibration intervals can be
increased accordingly. After the repeated calibration of the internal reference resistor over a period of 1 to
2 years its behaviour can be predicted with great accuracy.
Performing an automatic adjustment
You can adjust the internal reference resistor very easily by connecting an exactly known, certified standard
resistor and determining the new value of the internal reference resistor.
Equipment:
-
TTI-22
-
Standard resistor [100 Ohm or rather 400 Ohm]
-
Calibration certificate for the standard resistor certified by a bureau of standards [measuring
uncertainty < 1 ppm]
-
Thermostat with oil bath
1.
The standard resistor in the oil bath needs to be brought to the reference temperature stated in the
calibration certificate.
2.
Connect the standard resistor to sensor channel 1.
3.
Select the menu item 2 Edit Configuration > 2 Reference Resistor > 2 Adj. Int.
RRef.
Fig. E – 1 Adjusting reference resistor
4.
At Std. Res enter the standard resistor value according to the calibration certificate.
5.
Now press the <
> key.
6.
Wait approx. 1.5 minutes (50 measuring values).
The newly determined value of the internal reference resistor New Rref as well as the old value Old
Rref appear on the display.
7.
Note the old and the new reference resistor values and the current date.
8.
File these records with care.
9.
To continue, press the <
> key.
10. Press the <
> key again in order to store the new value for the internal reference resistor.
