RKI Instruments GD-K77D - Manual (Page 11)

Model GD-K77D Operator’s Manual Description • 6
The Model GD-K77D provides a three-wire 4-20mA signal output for a controller. The
Model GD-K77D-NT provides a two-wire digital signal which is used by the RM-77NT
accessory and is then converted to either an RS-232C or RS-485 signal. It has two gas
alarm levels, two sets of gas alarm relay contacts, a trouble alarm, and trouble relay
contacts.
The Model GD-K77D is a sample draw gas detection head. The Model GD-K77D draws in
the sample gas from a remote location using an internal pump. The flow system directs
the gas to an internal gas sensor. Various lengths of inlet tubing can be used, and tubing
length is determined by the target gas and the operating environment. When using the
Model GD-K77D in areas containing dust or other particulate contamination, use the
appropriate sample filter. The correct sample filter is dependent on the target gas.
Case
The Model GD-K77D has a rugged metal case. A sturdy wall mounting bracket is supplied
that allows the Model GD-K77D to be securely attached to a wall for convenient operation
and maintenance.
On the front of the case are four LEDs, a LED display, a flowmeter, and a large screw that
is used to open and close the case cover. On the bottom are located a gas inlet, a gas
exhaust, and two cable bushings for external wiring.
Alarm Lights
Four light-emitting diodes (LEDs) provide visual alarms for gas concentrations and
malfunctions, and are part of the detector panel along with the LED display. These LEDs
are located on the front of the unit in the upper left corner for greatest visibility. They
perform the following functions:
PW/TR. Indicates power on or off and warns that the Model GD-K77D is not operating
normally. When PW/TR is lit (green color), the Model GD-K77D is fully powered and is
operating normally. When the PW/TR is off, power to the Model GD-K77D has been shut
off. When the PW/TR is flickering, the Model GD-K77D is not operating normally.
• ALM1. Indicates the first gas alarm (orange color).
• ALM2. Indicates the second gas alarm (red color).
• SKIP. Indicates that the Model GD-K77D is in Maintenance Mode and has temporarily
stopped gas detection.
Display
An LED display shows gas concentration in parts per million (PPM). The LED display is
located on the front of the unit in the upper right corner for easy viewing.
Flowmeter
The flowmeter checks the sample flow rate of the target gas reaching the sensor inside
the Model GD-K77D. The flowmeter is a glass tube on which are marked two red flow
lines. A flow ball indicates whether the flow rate is within, or outside, the red flow lines.
During normal operation, the standard flow rate to the sensor is approximately 0.5 L/min,
and the flow ball should be within the two red flow lines. When the ball drops below the
bottom flow line, the Model GD-K77D cannot accurately detect the target gas. Increase
the flow rate. When the ball rises above the top flow line, reduce the flow rate. For more
information about adjusting the gas flow rate, see “Flow Adjustment Up/Down” under
“Internal and Back Panel Components.”