8
5.4 Diagnostic function
The unit continuously checks the temperature measurement
check function) and detects further events� In case of deviations from normal
operation, a diagnostic message is provided
5.4.1 Calibration check function
By measuring with two different, thermically coupled sensor elements (measuring
element and reference element) the unit automatically detects temperature
differences during temperature measurement�
The process value is measured by the measuring element and provided via the
analogue output�The reference value is used for comparison purposes and to
verify the process value� If the temperature difference between the process value
and the reference value exceeds the value set as calibration check limit [ccL], a
warning is triggered: The LED changes to blue and the diagnostic output opens�
t
T [°K]
CCL
2
1
Figure 2: Calibration check function
Example: Measuring element (1) measures 61�05 °C, reference element (2) measures 60 °C�
Setting ccL = 1 K results in a warning�
If a warning is triggered, the LED remains blue, even if the temperature
difference drops below the ccL value again� Corrective measures:
Check whether the sensor is to remain in use in the process or to be
replaced or do as follows:
►
Increase the ccL value so that the LED goes back to green�
> The diagnostic output closes�
> The ccL modification is written to the logbook
�
If the reference element fails, the calibration check function fails as well and
the LED changes to blue�
