Endress+Hauser iTEMP HART TMT142 Manuel De Mise En Service page 74

Trouble-shooting
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74
Note!
If several errors are present, the error with the highest priority is output. Once this error is
eliminated, the next error is output! An offset of 1000 indicates that more than one error is present.
Device behaviour in event of sensor error
In the event of a warning or error, the "Caution" symbol appears on the display and the error code
is shown. If an error occurs, the bargraph also flashes on the display and only the error code is
displayed and not the measured value. (See also Section 5.2).
9.2.1 Corrosion detection
Sensor connection cable corrosion can lead to false measured value readings. Therefore our unit
offers the possibility to recognise any corrosion before the measured values are affected.
There are 2 different steps selectable dependent on the application requirements:
• off (warning output just before reaching the alarm set point. This allows for preventative
maintenance/trouble-shooting to be done.)
• on (no warning, immediate alarm)
The following table describes how the device behaves when the resistance changes in a sensor
connection line, depending on whether on or off is selected.
Note!
Corrosion detection only for RTD with 4-wire connection
< ≈ 2 kΩ
1)
RTD
off ---
on ---
Pt100 = 100 Ω at 0°C / Pt1000 = 1000 Ω at 0°C
1)
< ≈ 10 kΩ
TC
off ---
on ---
1) If the ambient temperature is very high, it is possible to have a measured error 3 times that of the specified value.
The sensor resistance can have an effect on the resistance data in the table. If all the sensor
connection line resistances are increased simultaneously, the values described in the table are
halved.
In corrosion detection, it is assumed this is a slow process with a continuous increase in resistance.
9.2.2 Monitoring the supply voltage
If the necessary supply voltage is undershot, the analog output value drops approx. 3 s ≤ 3.6 mA.
Error code 19 appears on the display. Then the device attempts to output the normal analog output
value again. If the supply voltage remains too low, the analog output value drops again to ≤ 3.6 mA.
This prevents the device from constantly outputting an incorrect analog output value.
2 kΩ ≈ < x< ≈ 3 kΩ > ≈ 3 kΩ
WARNING ALARM
ALARM ALARM
10 kΩ ≈ < x< ≈ 15 kΩ > ≈ 15 kΩ
1)
WARNING ALARM
ALARM ALARM
TMT142
Endress+Hauser