8 • 35-3010A-13 Sample-Draw Detector
Charcoal Filter
The charcoal filter is located above the H
2
transmitter. It is held in place by a metal clip. The charcoal
filter is placed after the H
2
S sensor (if one is installed) and before the CO sensor (if one is installed) 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. It is included in this version of the sample draw detector in case a CO
sensor is added in the field. If a CO sensor is added in the field, a new charcoal filter should also be
installed.
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 1). A ball in the
flowmeter column indicates the flow rate of the sample-draw detector. 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 sensor.
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 1).
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 22 for instructions 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 of the incoming gas sample.
If the flow rate falls below the preset low flow level, the pressure switch causes the fail relay to
interrupt the signal in the 4-20 mA line for the CO and H
2
S channels (if installed). This causes a
downscale reading at the monitor on these channels. The low flow level is factory-set at 0.6 SCFH
(±0.2 SCFH).
NOTE:
There is no low flow indication for this version of the 35-3010.
