Analysis & Monitoring
Online and in-line analysers for water chemistry, gas composition and moisture - built for continuous duty in the process, not the laboratory.
A process analyser answers a chemistry question continuously, in the plant, without a sample being carried to a bench. pH, conductivity, dissolved oxygen, turbidity, residual chlorine, moisture and gas composition are all measured this way, and the result normally feeds a control loop, a dosing pump or a compliance record rather than a person.
What separates this category from laboratory analysis is the duty rather than the chemistry. An online analyser has to survive the sample as it actually arrives - hot, pressurised, carrying solids, gas slugs or fouling - and it is judged on drift and on the interval between services more than on the finest resolution it can display. A bench instrument measuring the same parameter can assume a clean, conditioned sample. An in-line instrument cannot.
Buyers arrive with a measurement point rather than a model: a tapping on a pipe, a tank, a basin or a stack. Most of the engineering that follows concerns the sample itself, because an analyser starved of a representative sample will report the wrong number reliably and consistently.
| Product type | How it measures | Usually specified for |
|---|---|---|
| pH analyser | Potential developed across a measuring and reference electrode pair, referred to a buffer calibration | Effluent neutralisation, chemical dosing and cooling water - any point where a control band is set around neutrality and the reference junction is the part that needs attention |
| ORP analyser | Potential on an inert electrode read against a reference, following the oxidant rather than the acid | Disinfection control, cyanide and chrome destruction, where the value tracks oxidising strength rather than pH |
| Conductivity analyser | Resistance across a cell of known geometry, corrected to a reference temperature | Demineraliser and reverse-osmosis monitoring, rinse water, concentration control and leak detection between two media |
| Dissolved oxygen analyser | Reduction current at a membrane-covered cell, or quenching of a luminescent spot | Aeration basin control, boiler feedwater and deaerator monitoring, and any dissolved-oxygen limit |
| Turbidity analyser | Light scattered at an angle by suspended particles, or the loss of transmitted light | Filter performance, final effluent, raw water intake and drinking-water treatment |
| Chlorine analyser | Colorimetric reaction with a reagent, or a membrane-covered amperometric cell | Disinfection control downstream of chlorination or dosing, potable water and process wash circuits |
| Moisture analyser | Capacitive, dewpoint or zirconia behaviour, with the sample conditioned upstream | Compressed air and instrument air, dryers and gas lines where condensation would damage what follows |
| Gas analyser | Non-dispersive infrared absorption, electrochemical cell, paramagnetic or zirconia measurement | Combustion trim, stack monitoring, process gas purity and biogas |
TDS and salinity meters, water quality analysers, oxygen and CO2 analysers and the sample conditioning accessories that sit in front of an analyser are listed under this category as well.
There is rarely a single correct instrument for a duty, but there is always a shortlist that can be justified and a set of answers that eliminates the rest. These are the questions that decide it.
| Technology | Best suited to | Limits | Typical measurement |
|---|---|---|---|
| Glass electrode (potentiometric) | General aqueous measurement with the widest body of operating experience | The reference junction fouls, dries out or becomes poisoned; a two-buffer calibration is needed rather than a single-point check | pH, ORP |
| ISFET solid-state electrode | Harsh or frequently cleaned service where a glass bulb would break | Sensitive to light and to running dry, and the maintenance routine differs from glass, so the two are not interchangeable in a procedure | pH |
| Amperometric membrane cell | Continuous dissolved oxygen and residual chlorine | Membrane and electrolyte are consumables; the flow past the membrane has to be stable or the reading drifts with it | Dissolved oxygen, chlorine |
| Optical scattering | Turbidity and suspended solids from low to high level | Reads the condition of the window as much as the water, so it depends on a clean and representative bypass | Turbidity, suspended solids |
| Colorimetric | Parameters that need a specific reagent reaction to become visible | Reagent consumption and shelf life; dosing lines have to be kept clear, and the interval between services is set by reagent volume | Chlorine and other colour-forming parameters |
| NDIR, zirconia and capacitive | Gas composition, combustion oxygen and dewpoint | Dust, condensate and aggressive components attack the cell unless they are conditioned out upstream first | CO2, CO, O2, moisture |
What is left after the technology is chosen is a list of values that only the installation can supply. These are the ones that change the model, the price or the lead time:
Specifications vary by model and application, so no performance figure is stated on this page. Where a parameter has not been documented for a particular model, the product page says so rather than filling the gap with a plausible number. Send the values above and we will return the ones the selected model actually holds.
Frequently asked
The questions that come up before an order rather than after it. If yours is not here, send it with the requirement and we will answer it in the quotation.
The duty, not the chemistry. An online analyser works on the sample as the process delivers it and is expected to run unattended, so its conditioning, its drift and its service interval are the deciding characteristics. A laboratory instrument works on a clean, prepared sample and is judged on resolution. The same parameter can therefore be specified two completely different ways, and it is worth stating at the enquiry which of the two the application actually needs.
Usually, and it should be quoted together with the analyser rather than after it. A sample outside the sensor limits - too hot, too high a pressure, carrying solids or gas slugs - will read incorrectly regardless of how good the analyser is. Send the conditions at the tapping point and we will say what has to sit between the tapping and the sensor.
It depends on the chemistry and on the service, and a clean water point is not comparable with a fouling effluent line, so the interval is set by experience on that point rather than by a general rule. What can be quoted is the routine the instrument supports: one-point or two-point calibration, automatic wash, and whether the sensor can be withdrawn while the process runs.
Multi-parameter transmitters are common for the water chemistry group, where pH, ORP, conductivity, dissolved oxygen and turbidity share a controller and a set of outputs. Gas and moisture measurement is normally a separate instrument. Where one unit covers several parameters, confirm that each sensor can still be replaced and calibrated on its own.
At minimum one isolated current loop per parameter and a relay for alarm or wash. Where the value is logged or reported for compliance, a digital link is worth having so that the recorded figure and the displayed figure are demonstrably the same one. State where the signal terminates and how many outputs are needed.
Not for a typical effluent or potable water point, but it is needed wherever the atmosphere is classified - a dosing room handling a flammable reagent, for example, or a gas measurement inside a process area. State the classification of the installation including any zone around the tapping, and the enclosure and electronics will be quoted to match it.
Available now
PHA-300 · pH Analyzers Reference listing
Continuous pH measurement with automatic temperature compensation, a differential or combined electrode and a 4-20 mA output for control or recording.
Send the specification and we will confirm the matching instrument, availability and lead time. Minimum order quantity is 1 pc.
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Send the technical detail and we will confirm availability, lead time and terms. In-stock items ship within 48 hours; customized specifications typically take 2-10 days. Minimum order quantity is 1 pc.