RKI Instruments M2A - Manual (Page 32)

27 M2A Transmitter Operator’s Manual
4 - 20 mA Signal Output Operation
The output at the S terminal of the power/signal terminal strip is a 4 - 20 mA signal that
corresponds to the detection range of the M2A. During normal operation, this signal tracks the gas
concentration on the OLED display.
There are several circumstances where the signal output will not track the display reading but will
behave as follows:
• When the M2A is in its warm-up period, the signal output will be fixed at 3.5 mA (zero) for all
gas types except oxygen. For oxygen types, the output will be fixed at 17.4 mA (20.9%
oxygen) while the M2A is in warm-up.
• When the M2A’s gas type is changed, the M2A will enter Configuration Mode for you to
verify the parameter settings. When you exit Configuration Mode, the display will indicate
NEEDS CALIBRATION and will continue to indicate this until Calibration Mode is entered
and a calibration is performed. In this situation, the signal output will be fixed at 3.5 mA for
LEL and toxic versions and 17.4 mA for oxygen versions from the time Gas Type Mode is
entered until the M2A is calibrated and returns to normal operation.
• If you enter Calibration Mode, Configuration Mode, Gas Type Mode, or Modbus Mode, the
signal output will be fixed at 3.5 mA for combustible gas, CO
2
, and toxic versions and 17.4
mA for oxygen versions until the M2A returns to normal operation.
• If the M2A’s input power decreases below 9.5 volts so that the M2A is in a low power alarm,
the signal output is fixed below 2.4 mA until the low power alarm is cleared.
• If the M2 goes into a fail condition, after a 30 second delay, the signal output is fixed below 2.4
mA until the fail alarm is cleared. During the 30 second delay, the signal output follows the
detector output. In the case of a downscale reading, the display and the signal output continue
to track the reading down to -99% of full scale (1.15 mA).