Detcon FP-424C - Manual (Page 11)

Material Requirements
*
Digital volt meter
* Jewelers type screwdriver
a) Declassify the area around the sensor.
b) Remove the junction box cover from the remote sensor enclosure (see figure 4).
c) Using the digital volt/ohm meter, measure the bridge voltage at the remote sensor terminal connector board
from the “White” terminal to the “Blue” terminal as shown in figure 4. Target voltage is 2.7 volts.
d) At the transmitter, adjust the “VOLT” potentiometer (see figure #5) to achieve a reading of 2.7 vdc
(±0.2v) at the remote sensor terminal connector board as described in item “c” above.
e) Replace the junction box cover on the remote sensor enclosure.
Bridge voltage set is complete. This procedure need only be done once after initial power up.
6.2 Initial Operational Tests
After a warm up period has been allowed for, the sensor should be checked to verify sensitivity to gas.
Material Requirements
*
Digital volt meter
* Jewelers type screwdriver
* Detcon PN 943-000006-132 Threaded Calibration Adapter
* Span Gas 50% LEL methane in air at a controlled flow rate of 200 ml/min.
a) Declassify the area around the sensor.
b) Remove the junction box cover.
c)
Measure the voltage between the bridge test points: The bridge voltage is factory set at 2.7V. Use the
“Temp” potentiometer to make adjustments if necessary. (Note: If the sensor head has been remotely
installed away from the transmitter, the bridge voltage must be measured at the sensor head instead of
the bridge test points. The voltage is measured between the blue and white wires and should be adjust-
ed to 2.7vdc.)
d) Measure the voltage between the signal test points: zero gas conditions should provide a reading of
between 39 and 40 mV DC. If necessary, adjust the zero potentiometer to achieve this reading.
e) If applicable, remove the rain shield or splash guard from the sensor housing.
f)
Attach the calibration adapter to the threaded sensor housing. Apply the test gas at a controlled flow rate of
200 ml/m. Observe that the signal voltage increases to a level of 80 mV DC or higher.
g) Remove the test gas and observe that the signal decreases to between 39 and 40 mV DC .
Initial operational tests are complete. Detcon Model series FP-424C sensors are pre-calibrated prior to ship-
Detcon Model FP-424C Combustible Gas Sensor PG.11
BRDG
FP-424C
+
% LEL
4-20 mA DC
T E
X
A
S
H O
U S
T O
N
VOLT
detcon inc.
ZERO
BRIDGE
SIGNAL
FLT
DET
FLT
FINE
COARSE
Figure #5