Measurement Equipments

Humidity Meter

Know how much water your air carries, and whether it comes from the weather or from your equipment.

Download brochure Download questionnaire
A stainless steel humidity and temperature probe with a threaded connection and a perforated sensor guard

Product overview

See the moisture in your air, before it reaches production

Our humidity meter measures the relative humidity (RH) and temperature of air or gas at the same point, in the same probe, and calculates the values that follow from them: dew point, absolute humidity and mixing ratio. In your compressed air plant it measures both the ambient conditions that set the water load entering your compressors and the moisture in the compressed air itself, at line pressure or in a sample expanded to atmosphere.

RH tells you how close air is to condensing, and it has no meaning without the temperature beside it, which is why the meter always reads both together. Measured at line pressure, the dew point it calculates is the pressure dew point (PDP) that ISO 8573-1:2010 uses to define water classes.

Air leaving a refrigerated drying stage at +3 °C PDP and reheated to 25 °C sits at about 24 % RH, in the most accurate part of the meter's 0–100 % range. Applied under the test methods of ISO 8573-3, the meter gives you the evidence that water class 4, 5 or 6 has been achieved, and records the ambient conditions that explain changes between seasons.

A humidity transmitter with a digital display reading temperature, relative humidity and pressure
  • 0–100 %Relative humidity measuring range
  • +3 °CPDP for ISO 8573-1:2010 water class 4
  • 2.3 timesThe water in 35 °C, 80 % RH intake air compared with 25 °C, 60 % RH
  • 640 kgCondensate a day from 1,000 m³/h drawn in at 35 °C, 80 % RH, compressed to 7 bar g

Benefits

The problems it solves

Every compressed air system turns water vapour from the atmosphere into liquid. Here is what happens when nobody measures it, and how the meter helps.

  • Water at the machine

    The problem

    Without a measured value, the first sign of a drying problem is water at a machine, a rusted valve or a rejected product batch.

    How it solves it

    A rising dew point reveals a fouled heat exchanger, failed drain or open bypass before liquid water reaches production.

  • Weather or equipment?

    The problem

    Intake air at 35 °C and 80 % RH carries 2.3 times the water of air at 25 °C and 60 % RH, so the load on your plant swings with the season.

    How it solves it

    Paired ambient and compressed air readings show whether wet air comes from the weather or from your equipment.

  • Proving your air class

    The problem

    Customers, auditors and equipment manufacturers specify air by ISO 8573-1:2010 water classes, which are defined by pressure dew point.

    How it solves it

    A measured PDP confirms water class 4, 5 or 6 (+3 °C, +7 °C or +10 °C PDP) for audits and customer specifications.

  • Condensation in panels

    The problem

    Condensation inside control panels, drives and switchgear causes tracking, short circuits and corroded contacts.

    How it solves it

    RH monitoring in compressor rooms and panels flags the condensation risk before faults occur.

  • Drains that cannot keep up

    The problem

    A compressor delivering 1,000 m³/h of free air drawn in at 35 °C and 80 % RH, compressed to 7 bar g and cooled back to 35 °C, condenses roughly 640 kg of water a day in its aftercooler, separator and receiver.

    How it solves it

    Intake readings quantify the water your drains and oil–water separators must handle each day.

  • Records for regulated plants

    The problem

    Food and pharmaceutical plants keep dew point and humidity records for HACCP and GMP.

    How it solves it

    Continuous logging gives you dated records that support GMP, HACCP and ISO 9001 documentation.

Where it’s used

From the compressor room to the production floor

Anywhere moisture in the air affects your equipment, your product or your records, the meter gives you a number to work with.

  • Robots welding a car body on an assembly line

    Automotive and general manufacturing

    Plant air for cylinders, tools and paint shops, checked at the point of use where condensate causes rust and finish defects.

  • Wine bottles moving along a bottling line

    Food and beverage

    Dew point records for HACCP, and RH in packing areas and ingredient stores where powders cake.

  • Yellow tablets spilling from a medicine bottle

    Pharmaceuticals

    Humidity in tablet compression, coating and capsule filling rooms, and in the utility air supplying them, for GMP environmental records.

  • A row of yarn winding machines in a textile mill

    Textiles

    Spinning and weaving halls held within RH bands to control yarn breakage and static, and the moisture of air-jet loom supply air.

  • Electricity pylons and power lines at sunset

    Power generation and utilities

    Switchgear rooms, cable basements and control buildings, where condensation causes tracking and corrosion.

  • Blue plastic bottle caps in a moulded tray

    Plastics and packaging

    Ambient RH around dryers and moulding machines, which affects the handling of hygroscopic resin.

Also compressed air system audits, dryer commissioning and service, electronics assembly, cold chain and warehousing, HVAC and building services, and laboratories and calibration rooms.

How it works

Absorb, sense, calculate

A thin polymer film takes up water from the air until it matches the humidity around it. The meter reads that as capacitance, pairs it with temperature, and works out the dew point.

How a humidity meter works: a probe inserted through an isolation ball valve sits in the compressed air at line pressure. Water vapour passes a porous top electrode into a thin polymer film and raises its capacitance, which the meter reads as relative humidity. A temperature element in the same probe measures temperature at the same point, and the meter calculates the pressure dew point, absolute humidity and mixing ratio. RH ≈32 % T 20 °C PDP +3 °C Compressed air lineIsolation ball valve7 bar g · 20 °C · PDP +3 °C Probe Humidity element, magnified H₂O in, to equilibrium Capacitorεr ≈ 3–4 dry · water ≈ 80 Temperatureelement1 K ≈ 6 % of RH Meterdew point · g/m³ · g/kg 12345 Compressed air, at line pressureWater vapour moleculesMeasurement signalTemperature element

  1. 1. Probe in the lineThe probe enters your compressed air through an isolation ball valve, so it sees the air at line pressure and can be withdrawn while the system runs. It is fitted in the top or side of the pipe, where liquid water cannot flood it.

  2. 2. Water enters the filmWater molecules pass through a thin, porous top electrode into a hygroscopic polymer film, until its water content is in equilibrium with the air around it. The film is only micrometres thick, so it settles quickly.

  3. 3. Capacitance becomes RHDry polymer has a relative permittivity of roughly 3 to 4, and water about 80. Every absorbed molecule raises the film's capacitance, close to linearly in RH, and the meter converts it to a reading from 0 to 100 %.

  4. 4. Temperature beside itA temperature element sits in the same probe, as close to the humidity element as possible. A 1 K difference between probe and air changes RH by about 6 % of the reading at 20 °C, so both are measured at one point.

  5. 5. Dew point and moreFrom RH and temperature, the meter calculates dew point, absolute humidity and mixing ratio. At line pressure the dew point is your PDP. For an expanded sample, you enter the line pressure and the meter converts the reading back to PDP.

Air at 7 bar g and +3 °C PDP reads about 32 % RH at 20 °C at line pressure, and about 4.1 % RH once expanded to atmosphere.

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.

Download brochure Download questionnaire

Keep exploring

More from our range

Equipment for every stage of your compressed air, and our own engineers to test, commission and look after it.

Why Settle for Mediocrity When You Can Partner with the Best?

We are more than just another industrial solutions provider. We’re a partner in your success. With decades of experience and a team of experts dedicated to providing comprehensive solutions from equipment to service and sourcing, we’re confident in our ability to help you optimize your performance and achieve your business goals.

Speak with an Expert