September 2007
14
HygroTrace Moisture Transmitter
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
v
using a
user-specified range. The default range is 0-100 ppb
v
;
that is, 4 mA represents the zero (0 ppb
v
), and 20 mA represents
the span (100 ppb
v
) value.
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).
