The Flowtech Guide to Industrial, Probe and Infrared Thermometers
Used for measuring temperature in industrial settings, industrial thermometers are usually more sturdy than laboratory thermometers. There are four main criteria to consider when selecting an industrial thermometer.
- Measurement range.
- Resolution of the readings (1°C, 0.1°C or 0.01°C).
- Response time.
- Accuracy level.
Different thermometer types feature different temperature sensors including liquid, gas, bimetal, electronic or infrared. Gas and liquid thermometers consist of a glass tube filled with either gas or liquid, which expands up the capillary as the temperature increases. There are several factors to take into account when selecting a liquid or gas thermometer. These include:
- Type of liquid: Alcohol-filled thermometers are safer than thermometers filled with mercury.
- Tube material: While glass thermometers are most common, some thermometers are made from stainless steel to ensure durability. These are usually rust-resistant and mountable.
- Level of gas or liquid: The amount of liquid or gas in the thermometer tube is dependent on the expansion coefficient of the substance, the tube area and the range of the temperature measurements.
Sometimes called IR thermometers, infrared thermometers offer a non-contact way of measuring the surface temperature of an object. More specifically, they work by reading the temperature sent by the infrared signals emitted by an object.
When taking measurements with an infrared thermometer, you have to take into account the emissivity of a material or its ability to emit thermal energy. The emissivity of heat energy is rated on a scale of 0 to 1.0, with 0 representing a highly reflective object and 1.0 representing a so-called blackbody that lacks any reflective power. The majority of organic, painted or oxidised surfaces have an emissivity of approximately 0.95.
If you are measuring the temperature of materials that are highly reflective, it is best to select a device that allows manual adjustments of emissivity levels. This will ensure that the device accommodates the emissivity of a given object or surface.
Another very important feature to think about when choosing an infrared thermometer is its field of view or the distance-to-spot ratio. The most common fields of view in infrared thermometers are 4:1, 8:1 and 30:1, although they can go up to 50:1. The greater the ratio, the further away you can stand to measure the temperature from a heat source.
There are a number of ways infrared thermometers are better suited for industrial use than conventional probe thermometers. They are not just easy and fast to use but also non-contact, which means that you can measure the temperature of an object from a distance. On the downside, they only measure surface temperature and cannot be used to measure temperature through a covering such as clingfilm, glass or polyester. In addition, they are not suitable for measuring air temperature.
Digital Thermometers and Probe Thermometers
A vast improvement on liquid and gas thermometers, probe thermometers are the most common thermometers in general use today. They are fast, accurate and inexpensive. While there are different digital thermometer sensors, the most popular in industrial use is the “resistance temperature detector that works on the principle that temperature changes the electrical resistance of metals. Industrial digital thermometers are often used to monitor hot water systems, refrigeration and air conditioning.
Digital thermometers designed for industrial use are usually sturdy enough to be used in a range of challenging situations and hazardous environments. Some can also fit a range of probe types such as thermocouples and thermistors (probe thermometers usually come with a pointed tip, making them ideal for insertion or immersion). Many industrial digital thermometers also come with features such as rubberised IP-rated housings, countdown timers and non-sparking material constructions.
It is important to remember that not all digital thermometers are intended for industrial use. While some home-use digital thermometers are specifically designed for taking body temperature, others aim to measure the temperature of food and liquid.
Designed for use in manufacturing plants and commercial kitchens, thermapens measure the internal temperature of food and drinks. Unlike standard kitchen thermometers, they feature sturdy construction and a thermocouple sensor. Since they are the fastest and most precise cooking thermometer on the market, they are a favourite kitchen tool of celebrity chefs and other professionals within the food industry. Thermapens not only read temperature within seconds, they often come with a 360-degree rotating display and an automatic sleep mode.
Electronic Temperature Instruments, or ETI, is a manufacturer of digital and infrared thermometers for the food industry. ETI thermometers often come with Bluetooth connectivity, as well as features such as moisture, humidity and pH meters and data loggers.
ETI thermometers use different data sensors including NTC thermistors, thermocouples and resistance temperature detectors. While thermocouple thermometers are the fastest at delivering readings, NTC thermistors and resistance temperature detector thermometers tend to be more accurate.
Infrared thermometers are a 20th-century invention with the first patent for a radiation thermometer dating back to 1901. The first commercial infrared thermometer hit the market in 1931.
Infrared thermometers were not invested in a single country or by a single person. Instead, the technology and the device is the result of a chain of developments. The first important step that eventually led to the invention of infrared thermometers was the discovery of radiation in the 19th century. Infrared thermometers in their recognisable form were not developed until the mid-20th century.
Designed to measure the surface temperature of objects by reading infrared energy, infrared thermometers are used in a huge variety of industries. Their main benefit is the fact that they can be used to measure the temperature of an object from a distance. This can be important if there are safety issues that need to be taken into account during the temperature measurement process. After all, high temperature can be a sign of malfunctioning mechanical equipment and electrical circuits. Infrared thermometers cannot be used to measure the internal temperature of objects.
Infrared thermometers do not need to come into direct contact with an object to measure its surface temperature. As such, they are useful for measuring the temperature of “objects that would be difficult to measure with a contact probe thermometer. This includes dangerous objects, objects in locations that are tricky to access and moving objects. Here are some more specific examples of the uses of infrared thermometers.
- Distance: Measuring the temperature of difficult to reach objects such as air conditioning units or electrical circuits or systems.
- Danger: Non-contact temperature measurements are ideal for monitoring equipment such as furnaces, boilers and process pipes.
- Movement: Recording the temperature of objects that are in motion such as rotating machinery.
Infrared thermometers measure temperature by detecting the surface radiation of objects. Each infrared thermometer features a lens that funnels thermal radiation into a sensor called thermopile, which transforms it into an electrical voltage. The final temperature measurement is based on this electrical signal. The final reading is then shown on the device’s LCD screen. Some infrared thermometers are designed to take into account external environmental factors that skew measurement results such as ambient air temperature.
Also referred to as heat radiation, infrared energy is emitted by most objects. Invisible to the eye, it makes up the electromagnetic spectrum. Infrared radiation can have different wavelengths, from a fraction of a micron to hundreds of microns. Infrared thermometers can measure infrared radiation with a wavelength from 4 to 14 microns.