RKI Instruments NP-204 - Manual (Page 10)

NP-204 RKI Instruments, Inc.
Calibration Supplies and Equipment
To adjust the NP-204, you will need the following supplies and equipment, some of which is available
in an RKI Calibration Kit:
• Known calibrating sample of 2.5% Volume (50% LEL) natural gas (methane) in air.
• A flowmeter with a range of 0 - 1.0 lpm (0-2.0 SCFH).
• A control valve for the cylinder, and a tubing length to connect the gas to the NP-204.
• A source of 100% natural gas or methane.
All the above items except the 100% natural gas source are available from RKI in a test kit. The 100%
natural gas source can be obtained by bleeding off a sample from a gas company, as piped to homes for
stoves or furnaces.
Calibration Procedure
Combustibles Span (Low range span)
1 . Take the NP-204 to a non-hazardous environment before calibrating.
2 . Loosen the two large screws on the top of the instrument, and separate the top
half of the case from the bottom case. Locate the potentiometer on the PCB marked
“SPAN (L)”
3 . Turn the instrument on to “VOLT ADJ.”, and adjust the voltage to the red Volt
Check line near the top of the meter. Turn the Range switch to “L”, allow two
minutes warm-up, and then Zero the reading using the external zero adjustment.
4 . Connect the hose and probe onto the instrument, and connect the span gas tubing
to the probe tube.
5 . Open the valve connected to the 50% LEL Methane span gas cylinder, and,
verifying flow with flowmeter, flow about 0.5 lpm through instrument.
6 . Adjust the SPAN (L) potentiometer if necessary to match the meter reading to
the span gas concentration. Turning the potentiometer clockwise increases the
reading.
Note
The combustible gas sensor is a general hydrocarbon sensor that responds to most flammable vapors
and gases; the response will vary depending upon the substance. See Appendix A for Relative
Response Curves for common gases and vapors, relative to a methane calibration.
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