4-20 Analog Output And Error Reporting - GE HygroTrace User Manual

September 2007

4-20 Analog Output and Error Reporting

The HygroTrace has a single 4-20 mA analog (recorder) output.
Normally, the output reports the measurement in ppb
user-specified range. The default range is 0-100 ppb
that is, 4 mA represents the zero (0 ppb
the span (100 ppb
The recorder output can exceed this range, within limits. A
measurement greater than the span will be reported up to
20.5 mA, and a reading below the zero will be reported down to
3.8 mA. Faults are indicated by readings outside this range.
These faults will be indicated by a 3.5 mA signal:
No Data - transmitter has not completed a measurement cycle,
•
so it cannot report.
No Calibration - transmitter was not programmed with
•
calibration data.
Out of Range - measurement cannot be determined with the
•
given calibration.
These faults will be indicated by a 21.1 mA signal:
Heater Fail Low - heater failed to reach the operating setpoint.
•
Heater Fail High - heater exceeded its operating limit.
•
Limits are taken from the NAMUR Recommendation NE 043.
Measurement is valid from 3.8 mA to 20.5 mA.
Fault is indicated by ≤3.6 mA or ≥21.0 mA.
The HygroTrace has a special operating mode used to dry the
sensor (see Sensor Dry Down on page 19). When in Dry Down
mode, the unit will report a fixed output of 20.5 mA, the
maximum valid measurement. When returned to normal
operation, the output returns to reporting the actual measurement.
In the case of a measurement exceeding the maximum calibration
value, the output will be limited to the maximum valid signal,
20.5 mA. The HygroTrace will never produce a negative reading
(less than 0 ppb).
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), and 20 mA represents
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HygroTrace Moisture Transmitter
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