35-3001A-05-XX CO
2
Sample-Draw Detector • 9
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 20 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 Carbon Dioxide Sensor/IR Carbon Dioxide Sensor PCB
The carbon dioxide sensor is an infrared type plug-in detector. The carbon dioxide sensor is installed in the
IR carbon dioxide flow block and the IR carbon dioxide flow block is mounted to the middle of the main
circuit board. A small circuit board, the IR carbon dioxide sensor PCB, with a 4-wire cable mates to the IR
carbon dioxide sensor and retains it in the flow block. The cable is wired to the main PCB. The IR carbon
dioxide sensor PCB allows you to replace the sensor without disconnecting the wiring.