How to choose a thermometer: infrared, digital or hygrometer

If you need to measure the temperature of a surface without touching it (motor, pipe, electrical panel), choose an infrared thermometer. If you need the temperature of a room or a cold room, choose a digital thermometer, preferably with min/max memory. If humidity matters too, take a thermo-hygrometer or a weather station. In the collection the resolution is 1 °C on the simplest models and 0.1 °C on the digital ones.

The types

• Infrared thermometers: they measure the surface temperature from a distance. There are models with a laser pointer such as the Fervi T068, and the Stanley STHT0-77365 and FatMax FMHT0-77422.
• Digital temperature meters: portable or pocket-sized, such as the Fervi T055, the T054 and the T063.
• Min/max thermometers: digital models that remember the lowest and highest temperature recorded over the period.
• Analogue room thermometers: wall-mounted or free-standing, in wood, plastic or metal, with no batteries. They are simple and never run flat, but they are read by eye and do not store anything.
• Hygrometers and thermo-hygrometers: they measure humidity. The Fervi I002 contact hygrometer detects it by touching the material; the FLIR MR176 thermo-hygrometer measures temperature and humidity together.
• Weather stations: multifunction and radio-controlled barometric versions to get more environmental data in a single instrument.
• Floating and medical thermometers: there are floating models and infrared thermometers for forehead or wrist measurement, intended for medical use.

How to choose by job

The features to look at

• Type of measurement: contact or at a distance, room or surface, temperature only or humidity too. It is the choice that matters most.
• Reading (resolution): in the collection you will find 1 °C, 0.1 °C and 0.1 % for humidity. For rough checks 1 °C is enough; for finer measurements you need 0.1 °C.
• Measuring range: it is not among the recurring data, but always look at it on the data sheet: a room instrument is not made for an oven or a boiler.
• Power supply: one 9 V battery or 4 AA batteries of 1.5 V each. Analogue instruments need none; digital ones do, so keep a supply of batteries to hand.
• Functions: min/max memory is useful for unattended checks; the laser pointer helps you see where you are measuring; readout in degrees Celsius and Fahrenheit is useful if you work with foreign documentation.
• Size and material: from pocket-sized (about 110 × 43 × 25 mm) to larger portable units; plastic, ABS, aluminium or stainless steel for the toughest uses.

Common mistakes

• Using an infrared thermometer to measure the air temperature: it measures the surface it is aimed at.
• Pointing the infrared thermometer at shiny metal or glass: reflective surfaces distort the reading.
• Measuring from too far away: the measured spot widens with distance and also includes what is around it.
• Putting the thermometer in the sun or near a heat source.
• Using a workshop instrument for measurements on people: for that you need a model intended for medical use.
• Relying on a single instrument for important decisions: if the figure matters, check it against a second instrument.

Frequently asked questions

Infrared or contact?

Infrared if the surface is hot, moving or out of reach. Contact or digital if you want the temperature of air, liquid or a room.

Where do I put the thermometer in the fridge?

In the centre of the shelf, and read it after a few minutes.

When do I change the batteries?

When the display gets faint, or before an important check.

How far away should I stand with an infrared thermometer?

The closer you are, the more the measurement covers only the spot you want. Check the data sheet for the ratio between distance and the diameter of the measured spot.

Do I need a calibration certificate?

If you need to document the measurements for an audit or a customer, ask the AMES technicians before ordering.

You will find all the models in the Thermometers and weather stations collection: if you are not sure which to take, ask the AMES technicians for a quote or advice.