RKI Instruments 35-3001A-01-02 - Manual (Page 9)

35-3001A-01-02 Combustible Gas Sample-Draw Detector • 5
counterclockwise to increase the flow and clockwise to decrease the flow.
Status LEDs
Two status LEDs are above the flowmeter. They are also visible through the window in the housing
door. The green Pilot LED is on when the sample-draw detector is receiving power from the
controller. The red Fail LED is on when the sample flow rate is below the low flow level.
Pressure Switch
The pressure switch is mounted to the back of the flowmeter circuit board. The pressure switch
monitors the flow rate of the incoming gas sample.
If the flow rate falls below the preset low flow level, the pressure switch causes the Fail LED to
turn on and interrupts the signal from the detector. The interrupted detector signal causes a fail
condition at the controller. The low flow level is factory-set at 0.6 SCFH (±0.1 SCFH). See
“Adjusting the Low Flow Setting” on page 17 to adjust this setting.
Pump Reset Switch
The pump reset switch is located to the left of the status LEDs. When a low flow condition occurs,
the pump will be shut off. To reset the low flow condition and start the pump again, press and hold
the pump reset switch for about 2 seconds, then release.
Hydrophobic Filter
The hydrophobic filter is located toward the bottom left of the main circuit board. The filter
prevents particulates and water in the incoming gas sample from damaging the flow and detection
systems. Replace the filter when it appears dirty, discolored, or clogged.
Pump
The pump is mounted to the right side of the main circuit board. The pump pulls the gas sample
into the sample-draw detector. The pump operates on 24 VAC, which is generated from the 24
VDC supplied by the controller.
IR HC Sensor/IR HC Sensor PCB
The combustible gas sensor is an infrared type plug-in detector. Infrared combustible detectors are
generally used instead of the catalytic combustible detectors in applications where there may be
catalyst poisons such as silicone present or where oxygen is not present in the monitoring
environment.
The IR HC sensor is installed in the IR HC flow block and the IR HC flow block is mounted to the
middle of the main circuit board. A small circuit board, the IR HC sensor PCB, with a 4-wire cable
mates to the IR HC sensor and retains it in the flow block. The cable is wired to the main PCB. The
IR HC sensor PCB allows you to replace the sensor without disconnecting the wiring.
Amplifier
The amplifier converts the electrical output from the sensor to a 4 to 20 mA signal that corresponds
to the detection range and transmits the signal to a gas monitoring controller. A label on the
amplifier indicates the detector drive current. This drive current is factory set. The amplifier is
mounted on the top middle edge of the main circuit board. It consists of the zero pot, span pot,
controller terminal strip, detector terminal strip, and test points.
Zero Pot
The zero pot is located in the upper right corner of the amplifier (see Figure 1). Use a small flat
blade screwdriver to turn the zero pot’s adjustment screw and adjust the amplifier’s zero (fresh air)
output during the start-up and calibration procedures. Turn the adjustment screw clockwise to
increase the fresh air output and counterclockwise to decrease the fresh air output.