35-3001-04 Carbon Monoxide 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.
Charcoal Filter
A charcoal filter is located at the bottom of the main circuit board, behind the hydrophobic filter. It
scrubs out interfering gases which may cause the CO sensor to respond, such as H
2
S or certain
hydrocarbons. Replace the charcoal filter when false high CO readings are noticed, especially in
the presence of H
2
S.
Carbon Monoxide Sensor/CO Amplifier
The carbon monoxide sensor is a plug-in sensor that plugs into the back of the CO amplifier. The
sensor and amplifier are retained in the flow block by two screws. The flow block is mounted to the
middle of the main circuit board.
Through a series of chemical and electronic reactions, the CO sensor produces a millivolt output
that is proportional to the detection range of the sample-draw detector. A red wire and a blue wire
extend from the CO amplifier and allow connection to the detector/amp terminal strip.
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