Since sensor program version 2.05, it is possible to set in the mA output settings a mA default output value that the instrument returns to in certain malfunction situations. The value can be set to a low or high mA value, e.g. 3.0 mA or 22 mA. The mA measurement always returns to the mA default output value when error message is SHORT-CIRCUIT, NO SIGNAL, TEMP MEASUREMENT FAULT or NO SENSOR. When mA output source is configured to concentration, also NO OPTICAL IMAGE, NO SAMPLE and PRISM COATED cause the mA measurement to return to the default mA output value.
NAMUR is an international association of users of automation in process industries. The association recommendation NE 43 promotes a standardization of the signal level for failure information. The goal of NE 43 is to set a basis for proactively using transmitter failure signals in process control strategies. Using these failure signals, instrument faults are separated from process measurements.
NAMUR NE 43 uses the 3.8 ‑ 20.5 mA signal range for measurement information, with ≥21 mA or ≤3.6 mA to indicate diagnostic failures. For more information, see the figure below. With that information, it is easier to detect a failure condition on a refractometer, for example, it clearly tells you whether you have an empty pipe or a failed instrument.
An optional secondary mA output default can be set for the NO SAMPLE state to differentiate it from the other messages that cause the measurement to revert to default mA.
The factory setting for secondary mA default is Disable. To implement secondary mA default, go to the mA output calibration section on the parameter page and set secondary default mode to NO SAMPLE and then set the mA output value desired. For more information, see Parameters.