RKI Instruments Digester Gas Monitor - Manual (Page 21)

Digester Gas Monitor Operator’s Manual Internal Description • 15
page 68 for instructions to use the Digester Gas Monitor in a Modbus system.
Ground Stud
The threaded ground stud is used for making connections to earth ground. It is located in
the lower right corner of the main PCB and is connected through the main PCB to the G
(ground) terminal on the AC terminal strip. It is also connected to each conduit hub with a
wire. A kep nut on the stud may be removed for installation of one or more user supplied
lugs to make wiring connections to earth ground. This stud is typically used to connect the
shield drain wire of shielded cable to earth ground at the Digester Gas Monitor.
Power Switch
The power switch is between the common/channel relays and the fuses (see Figure 5 on
page 12 and Figure 6 on page 14). The power switch turns the incoming AC power source
on and off at the Digester Gas Monitor. When the switch is up, the power is on.
Power Supply
The power supply is mounted to the power supply mounting plate which is located behind
the display PCB. The power supply mounting plate is mounted to the main PCB with four
standoffs. The power supply receives AC power from the external power source and
converts it to a DC voltage that is usable by the Digester Gas Monitor circuitry. A
polycarbonate cover prevents accidental contact with the AC terminals on the power
supply.
AC & DC Circuit Protection
Two AC fuses are used in the Digester Gas Monitor. The two fuses are located on the right
side of main PCB, between the power switch and the AC in terminal strip (see Figure 6 on
page 14). They cut off the incoming AC power in the event of a short circuit or other
electrical fault which causes a high current draw in the Digester Gas Monitor. They are
housed in vertical fuse holders and are held in each holder by a quarter turn cover. They
are fast blow fuses rated at 6 A, 250 V.
A polyswitch is used to protect the DC power input. It is located on the right side of the
main PCB above the AC fuses and is labelled on the PCB silkscreen as PS9. In the event
of a short circuit or other electrical fault which causes a high current draw in the Digester
Gas Monitor, the polyswitch will interrupt the DC power if the unit is powered from DC.
When the fault situation is corrected, the polyswitch resets and the unit will continue to
operate. The polyswitch is not user serviceable.
Regulator and Gauge
The regulator and gauge are located in the lower left corner of the Digester Gas Monitor
housing. The regulator’s maximum allowable inlet pressure is 300 PSI. A gauge above the
regulator indicates the output pressure (between 5 and 50 PSI). The output pressure, and
system flow, can be adjusted using the knob on the front of the regulator. The system flow
rises or falls as the output pressure is increased or decreased.
Flow Switch
The flow switch is located in the upper right corner of the Digester Gas Monitor housing.
The flow switch monitors the flow to the sensors and actuates if the flow rate goes below
1.6 SCFH.
Flow Block
The flow block is located in the center of the Digester Gas Monitor and is designed to
accept the gas sensors and route sample to each sensor. The methane, oxygen, and CO
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