RKI Instruments 35-3001A-02 - Manual (Page 9)

35-3001A-02 Oxygen Sample-Draw Detector • 5
flowmeter measures the flow in the range 0.2 to 2.0 SCFH (Standard Cubic Feet per Hour). The
optimum flow rate is 1.0 SCFH.
Sensor Flow Control Valve
The sensor flow control valve is mounted to the flowmeter circuit board above the flowmeter. The
sensor flow control valve adjusts the flow rate to the sensor. Turn the valve’s knob
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.
Oxygen Sensor
The oxygen sensor is installed in a flow block and the flow block is mounted to the middle of the
main circuit board. The oxygen sensor is retained in the flow block by a bracket with two screws.
The oxygen cell is protected within the sensor assembly. Through a series of chemical and
electronic reactions, the oxygen cell produces a millivolt output that is proportional to the detection
range of the sample-draw detector. The leads extending from the sensor are factory wired to the
oxygen sensor terminal strip.
Amplifier
The amplifier converts the electrical output from the detector to a 4 to 20 mA signal that
corresponds to the detection range and transmits the signal to a gas monitoring controller. The
amplifier is mounted on the top middle edge of the main circuit board. It consists of the zero pot,
span pot, controller terminal strip, detector terminal strip, and test points.
Zero Pot
The zero pot is located in the upper right corner of the amplifier (see Figure 1). Use a small flat
blade screwdriver to turn the zero pot’s adjustment screw and adjust the amplifier’s zero (oxygen
free) output during the calibration procedure. Turn the adjustment screw clockwise to increase the