Detcon FP-624D - Manual (Page 20)

Model FP-624D
FP-624D Instruction Manual Rev. 1.2 Page 16 of 42
3.3 Normal Operation
In normal operation, the display continuously shows the current sensor reading, which will normally appear as
“0”. Once every minute, the LED display will flash the sensor’s units of measure and the gas type (i.e. %
LEL). If the sensor is actively experiencing any diagnostic faults, a “Fault Detected” message will scroll
across the display once every minute instead of the units of measure and the gas type. At any time, while the
sensor is in “Fault Detected” mode, PGM1 or PGM2 can be swiped to prompt the sensor to display a list of the
active faults.
In normal operation, the 4-20mA current output linearly corresponds with the full-scale range.
3.4 Calibration Mode (AutoSpan)
Calibration Mode allows for sensor span calibration. Span calibration should be performed on a routine basis
(quarterly minimum) to ensure reliable performance. If a sensor has been exposed to any de-sensitizing gases
or to very high over-range combustible gas levels, then a re-calibration should be considered.
Unless
otherwise specified, span adjustment is recommended at 50% LEL. This function is called “AUTO SPAN.”
3.4.1 AutoZero
The AutoZero function is used to zero the sensor. Local ambient air can be used to zero calibrate the sensor as
long as it can be confirmed that it contains no combustible gases. If this cannot be confirmed then a zero air
cylinder should be used.
Material Requirements:
-Detcon PN 327-000000-000 MicroSafe™ Programming Magnet
-Detcon PN 613-120000-000 Splash Guard with integral Cal Port -OR-
-Detcon PN 943-000006-132 Threaded Calibration Adapter
-Detcon PN 942-001123-000 Zero Air cal gas or use ambient air if no combustible gas is present.
NOTE: The zero gas source should have a normal background concentration of 20.9% O2.
Pure Nitrogen gas standards should not be used or errors may result.
a) If the ambient air is known to contain no combustible gas content, then it can be used to zero calibrate. If
a zero gas cal cylinder is going to be used then attach the calibration adapter and set flow rate of 200-
500cc/min and let sensor purge for 1-2 minutes before executing the AutoZero.
b) From Normal Operation, enter Calibration Mode by holding the programming magnet over PGM1 for 3-4
seconds. Note, the “▲” prompt will show that the magnetic switch is activated during the 3 second hold
period. The display will then scroll “PGM1=Zero …PGM2=Span”. Hold the programming magnet over
PGM1 for 3-4 seconds once the “▲” prompt appears to execute AutoZero (or allow to timeout in 10
seconds if AutoZero is not desired).
NOTE: Upon entering Calibration Mode, the 4-20mA signal drops to 2mA and is held at this
level until the program returns to normal operation. The “In Calibration” bit in the Modbus
TM
Fault Status register will be set until the calibration is complete.