RKI Instruments Digester Gas Monitor - Manual (Page 22)

16 • Internal Description Digester Gas Monitor Operator’s Manual
sensors are retained in the flow block by brackets. The H
2
S sensor is retained by the O-
ring compression force of the O-rings it is inserted past. When viewed from the front of the
Digester Gas Monitor, the methane sensor is in the front right corner, the H
2
S sensor is in
the front left corner, the oxygen sensor is in the back right corner, and the CO
2
sensor is in
the back left corner.
Sensors
Infrared Methane (CH
4
) Sensor
The IR CH
4
sensor is an infrared type plug-in detector. The IR CH
4
sensor is installed in
the front right corner of the flow block when viewing the flow block from the front of the
Digester Gas Monitor. A small preamp circuit board with a 4-wire cable mates to the IR
CH
4
sensor and retains it in the flow block. The cable is wired to the main PCB. The
preamp circuit board allows you to replace the sensor without disconnecting the wiring.
Oxygen (O
2
) Sensor
The oxygen sensor is installed in the right back corner of the flow block when viewing the
flow block from the front of the Digester Gas Monitor. 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 Digester
Gas Monitor. The leads extending from the sensor terminate in a connector that leads to
the main PCB. The connector allows the sensor to be replaced without disconnecting the
wiring.
Carbon Dioxide (CO
2
) Sensor
The CO
2
sensor is an infrared type plug-in detector. The CO
2
sensor is installed in the
back left corner of the flow block when viewing the flow block from the front of the Digester
Gas Monitor. A small preamp circuit board with a 4-wire cable mates to the CO
2
sensor
and retains it in the flow block. The cable is wired to the main PCB. The preamp circuit
board allows you to replace the sensor without disconnecting the wiring.
Hydrogen Sulfide (H
2
S) Sensor
The hydrogen sulfide sensor is a plug-in sensor that plugs into the back of the H
2
S
preamp. The hydrogen sulfide sensor is installed in the front left corner of the flow block
when viewing the flow block from the front of the Digester Gas Monitor. The sensor and
preamp are retained in the flow block by two screws.
Through a series of chemical and electronic reactions, the H
2
S sensor produces a millivolt
output that is proportional to the detection range of the Digester Gas Monitor. The wires
extending from the amplifier are connected to the main PCB.
Flowmeters
Three flowmeters are part of the Digester Gas Monitor’s flow system.
Flow to Sensors Flowmeter
The Flow to Sensors flowmeter is located along the right side of the Digester Gas
Monitor’s flow system and indicates the flow rate being applied to the sensors. This flow
should always be 3.0 SCFH.
H
2
S Dilution Sample Flowmeter
The H
2
S Dilution Sample flowmeter is located in the middle left of the Digester Gas
Monitor’s flow system and indicates the sample flow rate to the H
2
S sensor. The