What Information Is Needed to Specify a Process Gas Analyzer?

A useful gas analyzer specification starts with the measurement task. Which components must be measured? What happens to the gas between the process and the instrument? How will the plant use the result?

Before requesting a process gas analyzer, gather information about the gas composition, operating conditions, sampling location, response time and control interfaces. These details help define whether the project needs an instrument alone, a sample conditioning panel or an integrated analyzer system.

This guide focuses on extractive gas analysis, where a sample is taken from the process and transported to an analyzer. In-situ measurement uses a different arrangement and should be evaluated against the same application requirements.

1. Define the purpose of the measurement

Start with the decision the measurement must support: process optimization, product quality, equipment operation or emissions monitoring. Identify where the result will be displayed, recorded or used by a control system.

These three applications have different requirements:

• Process gas analysis measures gas composition within an industrial process.
• A continuous emission monitoring system (CEMS) addresses emissions from a source. Identify the applicable monitoring requirements at the start. A request using the phrase “continuous emission measurement system” should clarify whether a CEMS is intended and what measurements and reporting are required.¹
• An air quality monitoring system (AQMS) evaluates ambient air. Its sampling locations and measurement objectives differ from those of a process analyzer or stack-monitoring installation.²

If a measurement will influence a protective function, identify that requirement explicitly. A standard analyzer and control connection should not be assumed to form a safety system.

2. List the components, ranges and measurement basis

Provide each component to be measured, its normal concentration, expected minimum and maximum, and any startup or upset conditions. Include the background gas composition where known, rather than listing only the target components.

Specify concentration units, such as ppmv or volume percent, and whether results are required on a wet or dry basis. If mass concentration or normalized results are requested, state the reference conditions and any required corrections. Explain the accuracy, repeatability or detection limit the application actually needs; these are different characteristics.

NDIR means non-dispersive infrared; NDUV means non-dispersive ultraviolet. Both use absorption in different spectral regions. Selection depends on the target gases, ranges, interfering components and instrument design. Naming either principle does not establish that a particular analyzer is suitable for the complete stream. Other measurement principles may be appropriate.³⁴

3. Describe conditions at the sampling point

Include normal and extreme temperature and pressure, clearly identifying gauge or absolute pressure. Describe moisture, dust, droplets, aerosols, corrosive constituents and any tendency to condense or deposit material.

Also explain how the stream changes during shutdown, startup, cleaning or switching between operating modes. An installation that works during steady operation still needs a defined response when the sample conditions leave the instrument’s allowable range.

Mark unknown values as unknown. A preliminary request with clearly identified gaps is more useful than a specification filled with assumptions.

4. Define the sample probe, sample gas line and conditioning

Show the proposed sample probe, also called a sampling probe, location on a drawing or photograph. Include the process connection, available insertion space, access for maintenance and approximate distance to the analyzer.

For the sample gas line, provide the route length, environment and elevation changes if known. The design must consider materials, transport delay, pressure losses and preservation of the components being measured.

Sample conditioning may involve filtration, pressure or flow control and temperature management. Cooling or drying is not a universal requirement: removing condensate can also remove water-soluble components and change the sample composition. A heated approach may be appropriate for some applications, but temperature requirements must be established for the actual stream and equipment.⁵

The destination of sample exhaust, condensate and any return flow also belongs in the scope. The illustration above is a functional overview, not an installation drawing; it omits these application-specific connections.

5. Specify response time and control interfaces

Describe how quickly the plant needs a usable result after the process changes. Analyzer response alone is not the complete system response: sample transport, conditioning volumes, switching and signal processing can also introduce delay.

For integration, provide:

• The existing PLC, DCS, HMI or data acquisition system.
• Required analog signals, digital communication and available interface documentation.
• Measurement units, scaling, update expectations and timestamp requirements.
• Required status signals, such as fault, maintenance, calibration or invalid measurement.
• How the receiving system should handle unavailable or invalid data.

A measurement value without its validity status can be difficult to interpret during maintenance or calibration. Agree on both the value and the accompanying status information.

6. Describe the installation and maintenance arrangements

Identify the installation location, indoor or outdoor environment, available space, utilities and site electrical requirements. Include the site’s hazardous-area classification where applicable; suitable equipment must be selected against the actual location requirements.

Define access for service, calibration arrangements, consumables and the responsibilities for installation, commissioning and ongoing maintenance. For a retrofit, include existing drawings and equipment information so that reusable components and interface constraints can be assessed.

7. Prepare a compact inquiry package

Information	What to send
Purpose	Process description, measurement objective and intended use of results
Gas	Components, background composition, ranges, units and wet/dry basis
Conditions	Temperature, pressure, moisture, contamination and operating variations
Sampling	Probe location, connection, line route and approximate distance
Integration	Response needs, existing controls, interfaces and required status signals
Site and scope	Environment, utilities, drawings, photographs, delivery scope and target schedule

You do not need to complete the engineering design before making contact. Send the information available and identify what still needs to be determined. This creates a clearer starting point for technical discussion and quotation.

Discuss your application with HMG

HMG’s main specialization is industrial gas analysis, alongside industrial automation and standalone equipment supply. Tell us whether you need a process gas analyzer, a sampling and conditioning assembly, an integrated analyzer cabinet or control-system integration.

Review our gas analysis capabilities, explore equipment supply, or send your application details. For an existing instrument or replacement request, include its manufacturer, model or part number and available documentation.

Technical references

1. US EPA — Continuous Emission Monitoring Systems
2. US EPA — Managing Air Quality: Ambient Air Monitoring
3. Siemens — ULTRAMAT 7 module: NDIR measurement principle
4. HORIBA — Non-Dispersive Ultraviolet Absorption Method (NDUV)
5. SICK — S700 operating instructions: sample conditioning and water-soluble components