10 • 35-3001A-13-XX CO
2
/CO Sample-Draw Detector
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 23 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.
Flow Baffle
A flow baffle is located at the bottom of the main circuit board, behind the hydrophobic filter. Its function is to
isolate the carbon monoxide sensor from vibrations in the flow line that are caused by the pump.
IR CO
2
Sensor/IR CO
2
Sensor PCB
The carbon dioxide sensor is an infrared type plug-in detector. It is installed in the IR CO
2
flow block and the IR
CO
2
flow block is mounted to the middle of the main circuit board. It is the lower of the two flow blocks
mounted to the main circuit board. A small circuit board, the IR CO
2
sensor PCB, with a 4-wire cable mates to
the IR CO
2
sensor and retains it in the flow block. The cable is wired to the IR CO
2
amplifier. The IR CO
2
sensor
PCB allows you to replace the sensor without disconnecting the wiring.
