RKI Instruments GP-204 User Manual

Gas Detection For Life

World Leader In Gas Detection & Sensor Technology

www.rkiinstruments.com

INSTRUCTION MANUAL

Model GP-204

Portable Combustible Gas Monitor

The accompanying instrument is sold and serviced in the USA by RKI Instruments, Inc. Please contact RKI
Instruments for any follow up service needs, including questions, warranty issues, repairs, and spare parts
and sensors. Thank you for selecting this fine instrument for your use. With proper care and maintenance,
it will provide you with many years of reliable service.

RKI Instruments, Inc. • 33248 Central Ave. Union City, CA • Phone [phone] • [phone] • Fax [phone]

Gas Detection For Life

1. GENERAL DESCRIPTION

The model GP-204 HAND HELD PORTABLE COMBUSTIBLE GAS DETECTOR is a compact battery
operated portable instrument used for taking an air sample and indicating the presence and concentration of
combustible gas. Samples of the air under test are drawn by means or a rubber aspirator bulb and analyzed
for combustible gas content on a heated platinum filament in a Wheatstone bridge measuring circuit. A
built-in meter indicates combustible gas content in units of explosibility. Power for operation or the
instrument is provided by two size “D” alkaline or Ni-Cad batteries. A probe and extension hose permit
withdrawal of samples from remote locations and the instrument fits in a compact leather case with over the
shoulder carrying strap. The model GP-204 is suitable and recommended for testing tanks, manholes,
vessels, pressure cylinders, pipelines, and other closed systems or confined spaces to determine presence
or absence of combustible gas. It is a valuable aid for safety of operations whenever combustible gases or
vapors are handled.

2. OPERATION

Before taking instrument on the job, check battery voltage. To check, put switch in VOLT ADJ position.
Meter should rise to the "CHECK" position near top of scale. Lift and turn VOLT ADJ control clockwise to
determine maximum voltage setting. If it cannot be set beyond mark, batteries need recharging or
replacement. Do not attempt to use instrument at all if voltage reading cannot be set up to mark.

If voltage is satisfactory, continue with the next steps of preliminary adjustment as follows:

A. Confirm operation of pilot light/meter illuminating lamp.

B. With sample inlet in fresh air, squeeze bulb several times to flush out any remaining gas.

C. Check zero setting by turning switch to ON position. Meter should read close to zero. Lift and
turn ZERO knob to bring reading to exactly 0.

D. Couple sampling hose to instrument inlet on left hand end, and connect probe to end of hose.
Hold finger over probe to block flow and squeeze bulb. Bulb should remain squeezed while finger
blocks inlet.

E. Admit a sample of some combustible gas to end of probe, and confirm that meter rises upscale.

Instrument is adjusted and ready to use. lt may be turned off and carried to the job.

To make a gas test, proceed as follows:

1) Turn to VOLT ADJ. position, adjust voltage if necessary, then turn to ON.

Hold probe within space to be tested. Squeeze bulb several times while watching meter, and

2)
observe maximum reading.

3) After completion of test, remove probe from test space, flush with fresh air for 4 or 5 squeezes of
bulb, and turn off.

RKI Instruments, Inc. • 33248 Central Ave. Union City, CA • Phone [phone] • [phone] • Fax [phone]

World Leader In Gas Detection & Sensor Technology

www.rkiinstruments.com

Gas Detection For Life

3. INTERPRETATION

Meter readings are taken on a scale graduated 0 - 100% LEL. The abbreviation L.E.L. stands for Lower
Explosive Limit, and represents the lowest concentration, which can be ignited by a source of ignition, hence
the lowest concentration which can produce an explosion. This quantity is also spoken of as the Lower
Flammable Limit (L. F. L.).

The model GP-204 is calibrated before shipment to read directly in percent L.E.L. of methane in air, based
on the known L.E.L. for methane of 5.0% by volume. That is, a 5.0% by volume will produce a reading of
100%, and smaller concentrations will read in proportion.

Other combustible gases will read in approximate terms of explosibility. For maximum accuracy, the unit
should be calibrated to the gas intended to be detected.

Concentrations may also be interpreted in terms of volume percent by multiplying the percent L.E.L. in the
sample (determined from the meter reading and the curve) by the published figure for L.E.L. in volume
percent. as noted on the curve. The maximum concentration allowable in a space where men are working
or where welding operations are carried out is primarily a matter of local regulation and of judgement based
on knowledge of conditions. A maximum reading of 10% or 20% is usually allowed. If 20% is selected, this
is often spoken of as a factor safety of 5, as the concentration must be increased five times before explosive
conditions are reached.

4. MAINTENANCE

A. Calibration and Adjustment

In addition to the normal operating controls found on the top panel, the following auxiliary controls are
available.

Calibration Potentiometer

This adjustment is used to set the meter reading to the desired level, while sampling a known
concentration or combustible gas. To access this adjustment, the top plate must be removed by
taking out the screws in each corner. The calibration potentiometer is a slotted-shaft control located
above the right upper corner of meter. Turn clockwise to increase meter reading.

B. Sensor replacement

The sensor assembly consists of an active filament and a similar but enclosed reference filament,
potted into a flame arrestor. It should be replaced if zero cannot be set within the range of the ZERO
ADJ., or if reading cannot be set high enough on a calibration gas sample using calibration
potentiometer. To replace:

1) Loosen the two panel hold-down screws. Remove and invert top panel.

With switch off, loosen (do not remove) the three screws holding the terminals for red,

2)
black and white wires. Pull wires from terminals.

3) Remove the four screws holding the rectangular sensor plate. Pull out sensor and replace
with the new one in same position. Check that the gasket is in place on chamber before
installation of new sensor. Install wires on terminals as before.

4) Turn instrument on and adjust zero.

RKI Instruments, Inc. • 33248 Central Ave. Union City, CA • Phone [phone] • [phone] • Fax [phone]

World Leader In Gas Detection & Sensor Technology

www.rkiinstruments.com