RKI Instruments GP-204 - Manual (Page 3)

Gas Detection For Life
RKI Instruments, Inc. • 33248 Central Ave. Union City, CA • Phone (510) 441-5656 • (800) 754-5165 • Fax (510) 441-5650
World Leader In Gas Detection & Sensor Technology
www.rkiinstruments.com
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.
2) With switch off, loosen (do not remove) the three screws holding the terminals for red,
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.