4 • 35-3010RK-01 Sample-Draw Detector
Charcoal Filter
The charcoal filter is located above the LEL transmitter. It is held in place by a metal clip.
The charcoal filter is placed after the H
2
S sensor and before the CO sensor in the flow
system. 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.
Pump
The pump is located to the left of the main circuit board near the bottom left of the
sample-draw detector. 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 to the sample
draw detector.
Flowmeter
The flowmeter is attached to the main circuit board near the top left corner (see Figure 3).
A ball in the flowmeter column indicates the flow rate to the sensors. The flowmeter
measures the flow in the range 0.2 to 2.0 SCFH (Standard Cubic Feet per Hour). Although
the sample-draw detector will operate down to a flow of 0.6 SCFH, the optimum flow rate
is 1.2 SCFH.
Bypass Valve
The bypass valve is to the left of the flowmeter. The bypass valve adjusts the flow rate to
the sensors. Use a flat-blade screwdriver to adjust the bypass valve.
NOTE:
The bypass valve allows fine adjustments of the flow rate. For a wider range of
adjustment, use the flow adjust potentiometer (see Figure 3).
Status Lights
Two status lights are above the flowmeter.
Pilot Light
The green Pilot light is on when the sample-draw detector is receiving power.
Fail Light
The red Fail light is on when the sample flow rate is below the low flow level.
NOTE:
The factory set low flow level is 0.6 SCFH (±0.2). See “Adjusting the Low Flow
Setting” on page 18 to adjust this setting.
Pressure Switch
The pressure switch is mounted to the opposite side of the main circuit board. The
pressure switch monitors the flow rate to the sensors.
If the flow rate falls below the preset low flow level, the pressure switch causes the fail
relay to interrupt the sensor signal for the LEL and oxygen channels and the 4-20 mA
signal for CO and H
2
S channels. This causes a downscale reading at the monitor on all
channels. The low flow level is factory-set at 0.6 SCFH (±0.2 SCFH).
