Analytical Industries GPR-7500 User Manual
GPR-7500 AIS
PPM H2S Transmitter
Advanced Instruments, Inc.
Owner’s Manual
2855 Metropolitan Place, Pomona, California 91767 USA ♦ Tel: 909-392-6900, Fax: 909-392-3665, email: info@aii1.com
Introduction
1 Quality Control Certification
2
Safety
3 Features & Specifications
4 Operation
5
Maintenance
6
Spare Parts
7
Troubleshooting
8 Warranty
9
Material Safety Data Sheets
10
Drawings
A/R
Explosion Proofing Electrical Connections
Appendix
A
Correlating readings – LCD display to 4-20mA signal
output
Appendix
B
H2S Scrubber, Sample System, Media MSDS
Appendix
F
Maintenance H2S Scrubber & Coalescing Filter
Appendix
G
Table of Contents
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The appendices referenced above are an integral part of the documentation, installation and maintenance of
this analyzer to comply with all applicable directives. It is important that users review these documents
before proceeding.
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1. Introduction
Your new hydrogen sulfide transmitter incorporates an advanced electrochemical sensor specific to
hydrogen sulfide along with state-of-the-art digital electronics designed to give you years of reliable precise
measurements of hydrogen sulfide in a variety of industrial applications. More importantly, it has been
constructed as intrinsically safe in accordance with ATEX Directives 94/9/EC for use in hazardous areas in
zone 1 Group C and D
The transmitter design also complies with NEC intrinsic safety standards for use in Class 1, Division 1,
Group C, D hazardous areas. Please refer to Appendix A for information on making electrical connections
that maintain the desired level of protection.
To obtain maximum performance from your new hydrogen sulfide transmitter, please read and follow the
guidelines provided in this Owner’s Manual.
Every effort has been made to select the most reliable state of the art materials and components, to design
the transmitter for superior performance and minimal cost of ownership. This transmitter was tested
thoroughly by the manufacturer prior to shipment for best performance.
However, modern electronic devices do require service from time to time. The warranty included herein plus
a staff of trained professional technicians to quickly service your transmitter is your assurance that we stand
behind every transmitter sold.
The serial number of this transmitter may be found on the inside the transmitter enclosure. You should note
the serial number in the space provided and retains this Owner’s Manual as a permanent record of your
purchase, for future reference and for warranty considerations.
Serial Number: _______________________
Advanced Instruments Inc. appreciates your business and pledges to make every effort to maintain the
highest possible quality standards with respect to product design, manufacturing and service.
3. General Safety & Installation
This section summarizes the essential precautions applicable to the GPR-7500 AIS Oxygen Transmitter.
Additional precautions specific to individual transmitter are contained in the following sections of this manual.
To operate the transmitter safely and obtain maximum performance follow the basic guidelines outlined in
this Owner’s Manual.
Caution: This symbol is used throughout the Owner’s Manual to Caution and alert the user to
recommended safety and/or operating guidelines.
Warning: This symbol is used throughout the Owner’s Manual to Warn and alert the user of the
presence of electrostatic discharge.
Danger: This symbol is used throughout the Owner’s Manual to identify sources of immediate
Danger such as the presence of hazardous voltages.
Read Instructions: Before operating the transmitter read the instructions.
Retain Instructions: The safety precautions and operating instructions found in the Owner’s Manual
should be retained for future reference.
Heed Warnings: Follow all warnings on the transmitter, accessories (if any) and in this Owner’s
Manual.
Follow Instructions: Observe all precautions and operating instructions. Failure to do so may result
in personal injury or damage to the transmitter.
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2. Quality Control Certification
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3. Maintenance
Serviceability: Except for replacing the hydrogen sulfide sensor, there are no parts inside the
transmitter for the operator to service.
Only trained personnel with the authorization of their supervisor should conduct maintenance.
H2S Sensor: DO NOT open the sensor. The sensor contains a corrosive liquid electrolyte that could be
harmful if touched or ingested, refer to the Material Safety Data Sheet contained in the Owner’s Manual
appendix. Avoid contact with any liquid or crystal type powder in or around the sensor or sensor housing, as
either could be a form of electrolyte. Leaking sensors should be disposed of in accordance with local
regulations.
Troubleshooting: Consult the guidelines in Section 8 for advice on the common operating errors
before concluding that your transmitter is faulty. Do not attempt to service the transmitter beyond those
means described in this Owner’s Manual.
Do not attempt to make repairs by yourself as this will void the warranty as per Section 10 and may result in
electrical shock, injury or damage. All other servicing should be referred to qualified service personnel.
Cleaning: The transmitter should be cleaned only as recommended by the manufacturer. Wipe off dust
and dirt from the outside of the unit with a soft damp cloth then dry immediately. Do not use solvents or
chemicals.
Non-use Period: If the transmitter is equipped with a range switch advance the switch to the OFF
position and disconnect the power when the transmitter is left unused for a long period of time.
Installation
This analyzer has been constructed in compliance with
EN 60079-0 : 2006
EN 60079-1 : 2004
EN 60079-11 : 2007
It must be installed in accordance with
EN 60079-14
Sampling Stream: Ensure the gas stream composition of the application is consistent with the
specifications and if in doubt, review the application and consult the factory before initiating the installation.
Note: In natural gas applications such as extraction and transmission, a low voltage current is applied to the
pipeline itself to inhibit corrosion of the pipeline. As a result, electronic devices connected to the pipeline can
be affected unless they are adequately grounded.
Contaminant Gases/Liquids in Sample Stream: A sample flow indicator with integral
metering valve is required upstream of the analyzer to remove any interfering gases such as oxides of sulfur
and nitrogen that can interfere with measurement. Sample must be free from any condensable liquid. With
gas streams containing condensable liquids, a coalescing filter must be installed upstream of the sensor.
Consult the factory for recommendations concerning the proper selection and installation of sample
conditioning requirements.
Expected Sensor Life: With reference to the publish specification located in Section 4 of this
manual, the expected life of all H2S sensors is predicated on the rate of loss of electrolyte from the sensor at
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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 770C 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 H2S 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 H2S 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
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 backpressure 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.
S in a flowing gas stream, the inlet sample
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Application, Positive-Pressure A flow indicator with integral metering valve positioned
upstream of the sensor is recommended for controlling the sample flow rate between 1-5 SCFH. If a
separate flow control valve and a flow indicator is used, position flow control valve upstream of the sensor
and position a flow indicator downstream of the sensor. If necessary, a pressure regulator upstream of the
flow control valve should be used to regulate the inlet pressure between 5-30 psig.
Flow rates of 1-5 SCFH cause no appreciable change in the H2S reading. However, flow rates above 5
SCFH may generate a slight backpressure on the sensor resulting in erroneous readings.
Caution: Do not place your finger over the vent (it pressurizes the sensor) to test the flow indicator when
gas is flowing to the sensor. Removing your finger (the restriction) generates a vacuum on the sensor and
may damage the sensor (voiding the sensor warranty).
Caution: If the analyzer is equipped with a coalescing filter as part of an optional sample
conditioning system, inlet pressure must not exceed 30 psig.
Application, Atmospheric or Slightly Negative-Pressure: For such measurements,
an optional external sample pump may be used upstream of the sensor to push the sample across the
sensor and out to atmosphere. However, if the sample pump can pull/push more than 5 SCFH, a flow
control must be used to control the sample flow. The flow control valve must be positioned in such a way
that it does not generate any vacuum on the sensor.
Caution: If the analyzer is equipped with a flow indicator with integral metering valve or a
metering flow control valve upstream of the sensor and the pump is installed downstream of
sensor- open the metering valve completely before turning the pump ON to avoid drawing a
vacuum on the sensor and placing an undue burden on the pump.
If pump loading is a consideration, a second throttle valve on the pump’s inlet side may be necessary to
provide a bypass path so the sample flow rate is within the above parameters.
Moisture & Particulates: Installation of a suitable coalescing or particulate filter is required to
remove condensation, moisture and/or particulates from the sample gas to prevent erroneous analysis
readings and damage to the sensor or other optional components. Moisture and/or particulates do not
necessarily damage the sensor. However, collection of moisture/particulate on the sensing surface can
block or inhibit the diffusion of sample gas into the sensor resulting in a reduction of sensor signal output
and the appearance of a sensor failure. Consult factory for recommendations concerning the proper
selection and installation of optional components.
Moisture and/or particulates generally can be removed from the sensor by removing the sensor from the
housing and either blowing gas on the sensing surface or gently wiping the sensing surface with a damped
cloth.
Mounting of the Transmitter: The transmitter is approved for indoor as well as outdoor use.
However, avoid mounting in an area where direct sun might heat up the analyzer beyond the recommended
operating temperature range. If possible, install a small hood over the analyzer for rain water drain and to
prevent over-heating of analyzer.
Gas Connections: The Inlet and outlet vent gas lines require 1/8” or ¼” stainless steel compression
type tube fittings. The sample inlet tubing must be metallic, preferably SS. The sample vent line may be of
SS or hard plastic tubing with low gas permeability.
Power Requirement: Supply power to the analyzer only as rated by the specification or markings on
the analyzer enclosure. The GPR-7500AIS is powered by 12-24 VDC or 100/230 VAC supply (check the QC
certificate to ensure the power requirement of your analyzer). The wiring that connects the analyzer to the
power source should be installed in accordance with recognized electrical standards. Ensure that the
analyzer case is properly grounded and meets the requirements for area classification where the analyzer is
installed. Never yank wiring to remove it from a terminal connection.
Power Consumption: The maximum power the analyzer consumes is no more than 7 Watts.
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4. Features & Specifications
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5. Operation
Principle of Operation
The GPR-7500AIS H2S Transmitter incorporates a variety of advanced electrochemical sensors. These
sensors are very specific to H2S and generate an electrical signal proportional to the amount of H2S present
in a gas stream. The selection of a particular type of sensor depends on the maximum concentration of H2S
contents in the sample stream. Consult the factory for recommendation.
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 of power input, signal output and the 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. Once connected, the intrinsic safety barriers limit the amount of power that flows
to and from the signal processing electronics effectively preventing an explosive condition. The analyzer
design conforms to the ATEX directive for equipment as intrinsically safe.
The GPR-7500AIS also meets the intrinsic safety standards required for use in Class 1, Division 1, Group C,
D hazardous areas.
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Advanced Electrochemical Sensor
Technology
All electrochemical sensors driven by a bias potential (three electrode configuration) function on the same
principle and are specific to a certain gas. They measure
the partial pressure of the target gas from low PPM to up to
1% levels in air, inert gases and gaseous hydrocarbons.
The target gas, in this case, Hydrogen Sulfide, diffuses into
the sensor through a diffusion limiting membrane, reacts
electrochemically at the sensing electrode and produces an
electrical current output proportional to the
H2Sconcentration in the gas phase. The sensor’s signal
output is linear over all measuring 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 the design and chemistry of
the sensor’s components add significant advantages to this
extremely versatile H2S sensing technology. The sensor maintains its sensitivity to with +/-5% of its span (it
does not sleep during continuous use; a typical symptom seen with conventional electrochemical H2S
sensors)) over a 1-3 months period. To maintain accuracy over the useful life of the sensor, calibrate the
sensor every 1-3 months. Under normal use, the sensor is expected lost from 18-24 months.
The H2S sensor recovers from an upset condition (exposure to very high H2S) to low PPM level in a matter
of few minutes.
Electronic
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. The result is a very stable signal that reflects H2S concentration in the
sample very accurately. Response time of 90% of full scale is less than 60 seconds on all ranges (actual
experience may vary due to the integrity of sample line connections, dead volume and flow rate selected)
under ambient analysis conditions. Sensitivity is typically 0.5% of full scale of the low range. The display has
the resolution of 0.1 PPM H2S (on 0-20 PPM Full scale range). The analog output signal may be recorded
by on external device via the 4-20 mA or optional 1-5V signal.
Sample System
The standard GPR-7500AIS is supplied without a sample conditioning system thereby giving users the
option of adding their own or purchasing a factory designed sample conditioning system, see section 2 QC
Certification for optional equipment ordered. Whatever the choice, the sample must be properly conditioned
before introducing it to the analyzer sampling system to ensure accurate measurements.
The GPR-7500AIS is generally supplied with a minimum of a sample flow control valve and a flow meter. A
coalescing filter (installed at the sample inlet) and an H2S scrubber (installed at the sample vent line to
remove H2S from sample before venting) are most common optional components. A pressure regulator,
with or without a pressure gauge is also available as an option. Users interested in adding their own sample
conditioning system should consult the factory. Advanced Instruments Inc. offers a full range of sample
handling, conditioning and expertise to meet your application requirements. Contact us at 909-392-6900 or
e-mail us at info@aii1.com for recommendation.
Calibration and Accuracy Overview
Single Point Calibration: As previously described, the electrochemical H
electrical current proportional to the H2S concentration in the sample gas. In the absence of H2S the sensor
exhibits an absolute zero, e.g. the sensor does not generate a current output in the absence of H2S. Given
these linearity and absolute zero properties, single point calibration is possible.
Sample Pressure: Since the sensor is sensitive to the partial pressure of H
output is a function of the number of molecules of H2S per unit volume. When sample is vented to the
atmosphere the sensor essentially remains at atmospheric pressure. However, a positive or negative
S sensor generates an
2
S in the sample gas, the
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pressure on the sensor will alter the output of the sensor and unless the sensor is calibrated under the same
analysis conditions, a significant error in measurements will occur.
For positive sample pressure applications, the sample pressure must be regulated by using a pressure
regulator. The sample pressure between 5-30 PSIG offers a good compromise between delivering a
reasonable gas flow (1-2 SCFH) and the ease of controlling the sample flow by using the integral flow
control valve. Any blockage of the sample vent line will cause an increase in the pressure at the sensor thus
causing erroneous readings. If sample is to be vented into a pipe above atmospheric pressure, a pressure
regulator set at 0.5 PSIG must be installed to maintain constant pressure on the sensor. For vent pressure
above0.5 PSIG, consult factory for proper selection of electronics.
Ambient Temperature: The rate at which H
Teflon membrane otherwise known as an ' H2S diffusion limiting barrier'. All diffusion processes are
temperature sensitive, therefore, the fact that the sensor's electrical output will vary with temperature is
normal. Under typical applications, this variation is relatively constant and the measurement accuracy
remains within the published specifications over the recommended operating rage of temperature. The
accuracy of +5% or better over an operating temperature range e.g., 5-45oC can be obtained. The
measurement accuracy will be the highest if the calibration and sampling are performed at similar
temperatures (a temperature variation of 10 ºC may produce an error of >+/-2% of full scale).
S molecules diffuse into the sensor is controlled by a
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Accuracy: In light of the above parameters, the overall accuracy of an analyzer is affected by two types
of errors, 'percent of reading errors', illustrated by Graph A below and the 'percent of full scale errors',
illustrated by Graph B. The percent of reading error is contributed by incorrect calibration procedure whereas
the percent of full scale error is contributed by tolerance in components and the measurement device. These
errors are 'spanned out' during calibration, especially when span calibration is done close to the top end of
the measuring range followed by a zero calibration.
Graph C illustrates these 'worse case' specifications that are typically used to develop an overall accuracy
statement of < 1% of full scale at constant temperature or < 5% over the operating temperature range. The
QC testing error at the factory is typically < 0.5% of full scale.
Example 1: Graph A, percent of reading error, this error is more pronounced when a span adjustment is
carried out at the lower end of the scale, e.g., when span calibration is done by 20 PPM span gas on a 100
PPM full scale range, any error at 20 PPM span gas would be multiplied by a factor of 5 (100/20) when
making measurements close to 100 PPM. Conversely, an error during a span adjustment close to the top
end of the range, e.g., at 100 PPM would reduce the error proportionately for measurements near the
bottom end of the range.
Graph B represents a constant error over the entire measuring range. This error is generally associated with
the measuring e.g., LCD and or calibrating devices, e.g., current simulator or current/voltage measuring
devices.
Graph C shows the overall accuracy of the measurement.
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