Operation
Calibration (
continued
)
Test Gas Mode (available with display only):
If it is desired to check the sensor for its re-
sponse without sending a gas concentration
signal to a remote display device, this can be
accomplished by placing the Model S104 into
the “Test Gas Mode”. Procedure for checking
the calibration:
l
Place the magnet over the GMI Logo on
the cover of the Model S104. Remove the
magnet when a flashing pair of bars, “-
-”, (see figure 18) appears on the display
(about three seconds).
figure 18
l
Apply the test gas to the sensor and the
value of the gas concentration will be
indicated by the flashing display in about
one to two minutes.
l
When the reading has stabilized and the
test is complete, remove the gas and the
unit will return to normal operation when
the concentration drops below 5% LEL.
The “test” gas concentration must be at least
10% LEL before the unit will complete the
test sequence. If the Model S104 is placed in
the Test Gas Mode and no gas is applied for
six minutes, the unit will revert to a Fault con-
dition. Re-applying the magnet over the GMI
Logo will return the unit to normal operation.
Calibration Equipment:
The Portable Purge Calibrator is a compact,
accurate and safe system containing no explo-
sive gas. The lecture bottle is filled with a
standard 50% LEL mixture of gas/air. Using a
known gas/air mixture reduces the likelihood
of error in field calibration. The hose and cup
adapter permits calibration without having to
remove the sensor. The following pre-mixed
calibration gases at approximately 50% LEL
are available, in a lecture bottle, at 1200 psia,
8.3 MPa maximum pressure.
l
Butadiene
l
Butane
l
Ethane
l
Hydrogen
l
Methane
l
Propane
Methane and Hydrogen lecture bottles may be
returned to General Monitors for refilling. It
will be necessary to specify the gas. Spare
bottles containing these gases may be ordered.
The Portable Calibration Chamber is a 3 li-
ter (3000 cc) sample chamber with a spring
driven mixing fan.
A porthole allows the
chamber to be placed on the sensor for calibra-
tion. A syringe is included for accurate meas-
urement of volatile test liquids.
Sensors
should be calibrated to a specific vapor for
greatest accuracy. A hydrocarbon sensor cali-
brated for 50% LEL Acetone, for example,
will detect all hydrocarbons and most combus-
tible solvent vapors.
It will accurately read
ONLY the % LEL of Acetone. The indicated
measures of volatile liquids in the next column
produces 50% LEL vapor mixtures at 75°
Fahrenheit (25° Celsius) temperature and
standard pressure when used with the Portable
Calibration Chamber. See Appendix, section
5.4.
13
GENERAL MONITORS
Model S104
