Analytical Industries GPR-1800 AIS ATEX Trace PPM Oxygen Analyzer - Manual (Page 6)

Advanced Instruments Inc.
6
5 Operation
Principle of Operation
The GPR-1800AIS oxygen transmitter incorporates a variety of ppm
range advanced galvanic fuel cell type sensors. The transmitter is
configured in two sections. The signal processing electronics and
sensor are housed in a general purpose NEMA 4X rated enclosure.
The terminals for incoming power, power supply, signal output, alarm
relay contacts and intrinsic safety barriers are mounted on a PCB
housed in an explosion proof enclosure.
The two sets of electronics are interconnected using an explosion
proof Y-fitting, explosion proof packing fiber and sealing cement –
see Appendix A. Once connected, the intrinsic safety barriers limit the
amount of voltage that flows to and from the signal processing
electronics effectively preventing an explosive condition and meets
the intrinsic safety standards required for use in Class 1, Division 1,
Groups B, C, D hazardous areas.
Advanced Galvanic Sensor Technology
The sensors function on the same principle and are specific for
oxygen. They measure the partial pressure of oxygen from low ppm to 100% levels in inert gases, gaseous hydrocarbons,
helium, hydrogen, mixed gases, acid gas streams and ambient air.
Oxygen, the fuel for this electrochemical transducer, diffusing into the sensor reacts chemically at the sensing electrode to
produce an electrical current output proportional to the oxygen concentration in the gas phase. The sensor’s signal output is
linear over all ranges and remains virtually constant over its useful life. The sensor requires no maintenance and is easily and
safely replaced at the end of its useful life.
Proprietary advancements in design and chemistry add significant advantages to an extremely versatile oxygen sensing
technology. Sensors for low ppm analysis recover from air to ppm levels in minutes, exhibit longer life and reliable quality. The
expected life of our new generation of percentage range sensors now range to five and ten years with faster response times
and greater stability. Another significant development involves expanding the operating temperature range for percentage range
sensors from -30°C to 50°C.
Electronics
The signal generated by the sensor is processed by state of the art low power micro-processor based digital circuitry. The first
stage amplifies the signal. The second stage eliminates the low frequency noise. The third stage employs a high frequency filter
and compensates for signal output variations caused by ambient temperature changes. The result is a very stable signal.
Sample oxygen is analyzed very accurately. Response time of 90% of full scale is less than 10 seconds (actual experience may
vary due to the integrity of sample line connections, dead volume and flow rate selected) on all ranges under ambient
monitoring conditions. Sensitivity is typically 0.5% of full scale low range. Oxygen readings may be recorded by an external
device via the 0-1V signal output jack.
The circuit for the 4-20mA signal output and two adjustable alarms is powered by a DC/DC transformer that requires a 12-28
VDC power source and separate wiring for the outputs. A loop power source is not sufficient to power to the circuit. The 4-
20mA output is also represented on full scale oxygen readings to an external device.
Sample System: