Measurement Equipments

Dew Point Meter

Know your air is dry, rather than hope it is, with a pressure dew point you can watch, record and show an auditor.

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A fixed dew point meter with a digital display, fitted on top of a copper air line

Product overview

Dryness you can prove, not assume

Our dew point meter measures how much water vapour your compressed air or technical gas contains and reports it as a dew point: the temperature at which that vapour would start to condense. Measured at line pressure, it is your pressure dew point, the figure that decides whether condensation can form anywhere in your network.

Fixed meters sit permanently at a dryer outlet or a critical branch and report continuously. Portable meters travel between sampling points for audits, dryer commissioning and fault finding. Both measure a small, continuous sample flowing over the sensor, so the reading follows the air actually in your pipe.

One reading is shown as pressure dew point, atmospheric dew point, ppm v/v or g/m³, and maps straight onto the water classes of ISO 8573-1:2010, from Class 1 at −70 °C to Class 6 at +10 °C.

A handheld dew point meter connected to a sampling point on a compressed air pipe
  • −40 °C PDP16 ppm v/v of water at 7 bar g
  • About 12 g/hWater in 1,000 m³/h of air at −40 °C PDP
  • Class 1 to 6ISO 8573-1:2010 water classes
  • Fixed or portableContinuous monitoring or spot checks

Benefits

Water you can’t see, measured

Air at +20 °C PDP and air at −40 °C PDP look identical in a pipe, yet the first carries about 180 times more water vapour. Here is what that hides, and how the meter shows it.

  • Dryer faults caught early

    The problem

    A failed dryer gives no visible sign: the air looks, sounds and flows the same, and water appears in pipes, instruments and product hours or days later.

    How it solves it

    A rising dew point is the first measurable sign, flagging dryer, drain and filter problems before liquid reaches your network.

  • Small drifts, large water loads

    The problem

    A desiccant dryer drifting from −40 °C to −20 °C PDP sends eight times more water downstream.

    How it solves it

    A trend over days reveals gradual decline, and a step change reveals a sudden failure or an opened bypass.

  • Audit-ready records

    The problem

    ISO 8573-1, BCAS Guideline 102, GMP, HACCP and medical air audits all ask for measured values, not assumptions.

    How it solves it

    Time-stamped readings, traceable to a calibrated reference, document your water class for audits and product release.

  • Moisture sources located

    The problem

    Water can enter downstream of the dryer through an open bypass, a cross-connection or a temporary compressor.

    How it solves it

    Comparing your dryer outlet with remote points shows where moisture is entering the network.

  • Lower drying energy

    The problem

    Purge air, regeneration heat and refrigeration all consume energy in proportion to the dryness produced.

    How it solves it

    Measured dew point lets a desiccant dryer extend its drying phase at part load, cutting purge air and heater consumption.

  • Confident commissioning

    The problem

    After a new dryer, fresh desiccant or pipe changes, wet air can reach production before anyone checks.

    How it solves it

    A reading confirms the specified dew point has been reached before your air is released to production.

Where it’s used

Wherever dry air is a requirement

From the dryer outlet to the point of use, the dew point meter proves the water class your process specifies.

  • Wine bottles moving along a bottling line

    Food and beverage

    BCAS Guideline 102 specifies −40 °C PDP for air in direct contact with food, and dew point records support HACCP plans.

  • Yellow tablets spilling from a medicine bottle

    Pharmaceuticals

    Tablet coating, granulation, capsule filling and product blanketing, where GMP requires documented, calibrated measurement.

  • Test tubes of coloured chemicals in a laboratory rack

    Oil, gas and petrochemicals

    Instrument air to ISA-7.0.01: a line-pressure dew point at least 10 °C below the lowest ambient, and never above +4 °C.

  • Electricity pylons and power lines at sunset

    Power and electrical

    Instrument air in power plants, and moisture checks on the dry air and nitrogen used in switchgear and transformers.

  • Blue plastic bottle caps in a moulded tray

    Plastics

    Dry air for hygroscopic resin drying and PET preform blowing.

  • Robots welding a car body on an assembly line

    Automotive and surface finishing

    Spray painting and powder coating lines, where moisture causes blistering and poor adhesion.

Also compressor rooms in every industry, hospital medical air, breathing air to EN 12021, clean dry air at −70 °C PDP in electronics, feed air for nitrogen and ozone generators, and laboratory purge and analyser air.

How it works

Sample, sense, convert

A small, steady sample of your air flows over a humidity sensor held at line pressure. What the sensor reads becomes a dew point you can check against any specification.

How a dew point meter works: a small sample is taken from the top of the pipe through a ball valve into a measuring chamber at line pressure and bled away through a flow restrictor. In the capacitive sensor, water molecules pass through a porous electrode into a polymer film and raise its capacitance, while a platinum element measures temperature. The meter turns relative humidity and temperature into the pressure dew point, and converts it to atmospheric dew point and ppm. −40 °C PDP −57 °C atmospheric16 ppm v/vISO 8573-1 Class 2 Dry air from the dryerTo your network Ball valveSample line MeasuringchamberFlow restrictorLine pressure Porous electrodePolymer filmBase electrodePlatinum elementWater vapourInside the sensor 0.55 % RH at 20 °C12.8 Pa Dew point meter 12345Dry compressed airWater moleculesMeasurement signalSample bled to atmosphere

  1. 1. Take the sampleThe sample is taken from the top of the pipe, so any liquid runs past, through a briefly purged ball valve and a short stainless steel or PTFE line.

  2. 2. Hold line pressureThe sensor sits in a measuring chamber at line pressure, so it reads the pressure dew point directly. A flow restrictor after it bleeds a few litres per minute to atmosphere, keeping the sample fresh.

  3. 3. Sense the waterWater molecules pass through a porous top electrode into a thin polymer film. Water has a permittivity of about 80 against 3–4 for the dry film, so the capacitance rises with the relative humidity at the sensor, while a platinum element measures its temperature.

  4. 4. Calculate the dew pointFrom relative humidity and temperature, the meter finds the water vapour partial pressure, then the temperature at which it would condense. With the sensor at 20 °C, 0.55 % RH means 12.8 Pa and a pressure dew point of −40 °C.

  5. 5. Convert and recordEnter the line pressure and the meter converts: −40 °C PDP at 7 bar g is about −57 °C atmospheric dew point and 16 ppm v/v, ISO 8573-1 water Class 2. Record it once the reading has stopped falling.

Example figures for a dryer outlet at 7 bar g, with the sensor at line pressure and 20 °C.

Get the full details

Our brochure covers it in detail, and our questionnaire tells us what we need to recommend the right one for your plant.

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