Analytical Industries GPR-7500 AIS Trace PPM Hydrogen Sulfide Analyzer - Manual (Page 6)

Advanced Instruments, Inc.
6
temperature of 77°F/25°C and pressure of1 atmosphere in “normal” applications. Deviations from standard
conditions will affect the life of the sensor (temperature higher than 77 0 C and pressure less than
atmospheric would cause a reduction in the sensor life).
Accuracy and Calibration:
Refer to section 5 Operation.
Material and Gases:
Assemble the necessary zero, sample and span gases and optional
components such as valves, coalescing or particulate filters, and pumps as dictated by the application.
Stainless steel tubing is essential for maintaining the integrity of the gas stream for low PPM H
2
S level
analysis.
Operating Temperature: The sample must be sufficiently cooled before it enters the analyzer
and any optional components. A coiled 10 foot length of ¼” stainless steel tubing is sufficient for
cooling sample gases as high as 1,800 ºF to ambient. The recommended operating temperature
is below 35 ºC. However, the analyzer may be operated at temperature up to 45 ºC on an intermittent basis
but the user is expected to accept a reduction in expected sensor life
–as a rule of thumb, for every degree
ºC increase in temperature (above 25 ºC), the sensor life is reduced by approximately 2.5%.
Heat:
Install the analyzer away from direct sun and from any source of heat. Situate and store the
analyzer away from direct sources of heat.
Liquid and Solid Object Entry:
The analyzer should not be immersed in any liquid. Care should
be taken so that liquids are not spilled into and objects do not fall on or inside of the analyzer.
Handling: Do not use force when using the switches, knobs or other mechanical components. Before
moving your analyzer be sure to disconnect the wiring/power cord and any cables connected to the output
terminals of the analyzer.
Sample Pressure and Flow
All electrochemical sensors respond to partial pressure changes in the gas of interest. The sensors are
equally capable of analyzing the H
2
S content of a flowing sample gas stream or monitoring the H2S
concentration in ambient air (such as a confined space in a control room or an open area around a landfill or
bio-pond). The following is applicable to analyzers equipped with electrochemical sensors.
Analyzers designed for in-situ ambient or area monitoring has no real sample inlet and vent. The sensor is
exposed directly to the sample gas and it is intended to operate at atmospheric pressure. The analyzer has
a built-in pressure sensor and the sensor output is automatically compensated for any atmospheric pressure
changes. The analyzers function equally well with sample gas flowing across the sensor provided the
sample does not produce any positive pressure or create a partial vacuum on the sensor. For positive
sample pressure applications, suitable means must be employed to control the sample flow without
subjecting the sensor to high sample pressure. For applications where the sample is less than atmospheric
pressure, consult factory before initiating installation.
Inlet Pressure : For the analyzers designed to measure H
2
S in a flowing gas stream, the inlet sample
pressure must be regulated between 5-30 psig. Although the rating of the SS tubing and tube fittings/valves
itself is considerably higher (more than 100 psig), a sample pressure of 5-30 psig is recommended for ease
of control of sample flow.
The analyzer equipped with a sample system has designated SAMPLE and VENT ports. Connect SAMPLE
gas to SAMPLE and the vent to the VENT ports only.
Caution: If the analyzer is equipped with an optional coalescing filter, sample inlet pressure
must not exceed 30 psig.
Outlet Pressure : In applications where sample pressure is positive, the sample must be vented to an
exhaust pipe at a pressure less than the inlet pressure so that the sample gas can flow through the sensor
housing. Ideally, the sample must be vented to atmospheric pressure.
Note: The sensor may be used at a slight positive pressure (e.g., when sample is vented to a common
exhaust where the pressure might be higher than 1 atmosphere). However, the pressure at the sensor must
be maintained at all times including during the span calibration. This may be accomplished by using a back-
pressure regulator, (set at no greater than 0.5 PSIG) at vent line of the analyzer. Caution: A sudden
change in pressure at the sensor may result in the sensor electrolyte leakage and permanent damage to the
sensor.