WIKA TR21 Operating Instructions Manual page 17

6. Commissioning, operation
6.3 Behaviour of the electrical output signal
Sensor break and short-circuit
■
Sensor break or short-circuit are signalled after positive detection (after
approx. 1 second). If this fault condition has been caused by a malfunction, then a
relevant measurement signal must exist for approx. 1 second in order to return to
measuring mode. From the time of the error detection up to the error signalling, the last
relevant measured value will be delivered on the current loop.
Therefore, in the event of a "true" sensor break or short-circuit, this is also signalled
permanently. In the event of a "false" sensor break or short-circuit, the transmitter has the
possibility of reverting to measuring mode.
Medium temperature outside the span
■
If the media temperature configured in the transmitter is exceeded, the transmitter will
operate in a linear fashion within the following limits: 3.8 mA (MRS); 20.5 mA (MRE). If
these limits are crossed, then an error is signalled.
Hysteresis on return to the measuring span
■
After the linear error limits have been exceeded, on return to the measuring span, a
hysteresis of 0.1 mA must be passed. This hysteresis prevents the transmitter from
jumping back and forth between error and measuring mode.
Error
signalling
Error signalling
WIKA operating instructions model TR21
3.8 mA 4 mA
3.8 ...
4 ... 20 mA
4 mA
Measuring mode
3.9 mA
Error limits and permissible measuring range
20 mA 20.5 mA
Error
20 ... 20.5 mA
signalling
Error signalling
20.4 mA
EN
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