Infrared thermometers are able to measure the temperature of objects without making direct contact because they measure the energy objects radiate. Everything that has a temperature above absolute zero (-273.15°C / -459.67°F) emits infrared energy. The hotter it is, the more infrared energy it emits.
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In simple terms, the basic components of an infrared thermometer, or Pyrometer, consist of an optical system, a detector and a processing unit. The infrared energy emitted from the object to be measured is gathered by the optical system and then passed through to the detector which transforms the infrared energy into electrical signals. These signals are then changed in the processing unit into a temperature measurement.
Infrared thermometers are often referred to as ‘non-contact’ infrared thermometers and are also known by a range of other terms including:
- digital infrared thermometers
- digital pyrometers
- wireless thermometers
- wireless digital thermometers
- temperature guns
Pyrometers were first invented in the 18th Century to measure the temperature in pottery kilns and over time their application extended within industrial, manufacturing and engineering settings where traditional thermometers could not be used, or were not as effective, such as with an object:
- of high temperature where no direct contact with the heat source was possible
- which was moving (e.g. machinery or located on a conveyor belt)
- located where access was extremely limited
- containing hazardous or aggressive materials, such as high voltage parts or acids in chemical processes
There are many other advantages to using an infrared thermometer compared to those methods where direct contact is required and for many industries temperature is an important variable in terms of product quality, manufacturing efficiency and as a diagnostic tool in maintenance processes.
Coming in a range of shapes and sizes and with a variety of features, there are numerous factors to consider when purchasing a digital pyrometer subject to its intended application. Recent innovations and advances in technology have only broadened their scope of professional application even further, while also lowering the cost and widening their appeal to a completely new group of users.
How to Use: Basic Steps
One of the greatest assets of the modern hand-held wireless thermometer lies with the fact that they are relatively simple to operate. It is important however that users first familiarize themselves with the individual functions of each model and the operating instructions so that they are able to get optimum performance from their unit and its features.
Some of the more basic operating instructions for common features of an infrared thermometer are included below.
- Powering Up
Infrared thermometers are powered by batteries. Most models operate either on AA, AAA or 9-volt alkaline batteries while some are powered by rechargeable lithium batteries.
The vast majority of brands include a battery (or batteries) with the unit at the point of sale, however with some of the less-expensive, entry-level models, batteries will need to be purchased separately.
It goes without saying that batteries must be installed to the thermometer prior to use. Batteries are generally housed in the handle of the unit and the battery compartment cover can usually be removed by pushing on the handle where there is small indent on either side of the handle and then pushing down.
For those individuals who only intend to operate their IR thermometer on very rare occasion, it is recommended that the batteries be removed after use to prevent leakage and potential damage to the unit.
- Turning The Unit On and Off
Once the battery is correctly installed, most brands of wireless digital thermometers simply require users to engage the trigger mechanism in order to turn the unit on and begin operation. An automatic shut-off feature is typically included in all models which will turn the unit off after a set period of time (usually between 7 and 15 seconds).
- Selecting Unit of Measurement
Infrared thermometers typically allow users to be able to change the unit of temperature between Celsius and Fahrenheit subject to their individual requirements. Most models use Fahrenheit as the default, or pre-set unit of measurement and the LCD screen will generally have either a °C or °F symbol displayed to confirm the current setting.
To change the unit of measurement, users should refer to the instruction manual accompanying their infrared thermometer. In most cases however, once the unit has been turned on and LCD screen comes on, users can change the temperature scale by pushing the function buttons underneath the LCD display marked “°C/°F” until it is the correct setting for the application.
For those models that do not have a “°C/°F” function button, there is typically a switch contained in the battery compartment which can be used to adjust this setting.
As a general rule, the thermometer will recall the most recent temperature setting even after the unit has been turned off and will not divert to its default settings.
- Laser Pointer and Backlight
Most models come with either a single or dual red laser pointer to assist with aiming the digital pyrometer and a backlight to enable the LCD display to be visible in dark or low-light environments.
In some units these two features are permanently enabled and cannot be turned on or off manually. In others, these features can be manually adjusted either via the feature buttons underneath the LCD display or switches located inside the battery compartment. Separate symbols will usually be displayed on the LCD screen when these features are turned on.
- Measuring a Temperature
To measure a temperature, all that is required is to point the unit at an object and pull the trigger. The temperature reading will usually appear on the LCD screen in less than a second.
Once the trigger is released, the reading will normally continue to be displayed on the LCD until a new temperature measurement is taken, or the unit automatically shuts itself off after a pre-set time.
If using a single laser pointer to assist with aiming, it is important to note that some models set the laser a small distance from the center of the temperature measurement. With a dual laser pointer, the area in between the laser dots will often be the spot where the unit will take its measurement. As there are slight differences between models, it is recommended that users review the instruction manual prior to operation to ensure that they will be taking the temperature measurement from the correct area.
It is also important to consider the distance-to-spot ratio of the unit prior to taking a temperature measurement. Further discussion on distance-to-spot ratio and field of view can be found in “Factors to Consider Prior to Purchase”.
There are more advanced features which accompany certain models of wireless digital thermometers which are beyond the scope of this basic set of instructions. Emissivity is one feature of all infrared thermometers which are a major factor in temperature measurement and has been reserved its own special section for a detailed explanation.
Factors To Consider Prior To Purchase
One of the first considerations a prospective buyer of an infrared thermometer should take into account is the range of temperatures that the unit is able to measure. Obviously if the thermometer is unable to read temperatures of the upper or lower limits required by the end user then it will not be suitable. That said, the growth in the number of models available on the market allows for great variety in choice to the consumer.
Traditionally pyrometers were designed to measure the surface temperatures of objects with a very high temperature however with the advancement of technology has come the innovation to also allow for the measurement of materials which may be extremely cold.
Many models of infrared thermometers can comfortably measure temperatures within a range of -50°C to 500°C (-58°F to 932°F), however premium models offer a user the ability to measure temperatures in excess of 1,000°C. Again the primary consideration is the intended application of the device and the budget of a prospective buyer.
Many applications for wireless digital thermometers requires extremely accurate temperature measurements to be taken. This may not only the case for many professionals, but the general consumer as well. One important factor that influences the accuracy of a unit is emissivity.
When it comes to infrared pyrometers they can be divided into two separate groups. Those units which have a fixed emissivity and those that have an adjustable one.
In very simple terms, not all objects emit infrared energy equally. The type of surfaces (e.g. metals, non-metals, transparent objects) and other factors can influence the amount of infrared energy that is emitted. Emissivity refers to the efficiency with which a material emits or absorbs infrared energy.
Infrared thermometers make an adjustment to take into account these factors via the emissivity settings and the question of whether potential users require a unit with fixed or adjustable settings will depends on their intended application.
A review of ‘Emissivity Explained’ and ‘What is Emissivity?’ will provide prospective buyers with all the information they need when considering this important feature of infrared thermometers.
Distance-to-spot Ratio / Field of View
Another important factor which can influence the accuracy of readings from an infrared thermometer is the distance-to-spot ratio (D/S Ratio).
This ratio is the size of the area to be measured as it relates to distance. In other words, the target object being measured will grow larger as the distance between it and the thermometer increases.
To use an example of how the ratio is calculated and works, if you have a unit which has a D/S ratio of 10:1 and the target object proposed to be measured is 5 inches in size, the maximum distance the infrared thermometer can reliably measure the surface temperature is 50 inches. At any greater distance away from the target object not only will the thermometer measure the temperature of the target object, but also any surfaces immediately around it which fall within its field of view. This will therefore skew the temperature readings.
To the extent that an intended application requires a user to have to stand at a distance from the object being measured because it’s located in a hard-to-reach spot, or for workplace health and safety considerations due to the hazardous nature of the object, then it is important to purchase a unit which has the appropriate D/S ratio.
Manufacturer’s Warranty / Returns Policy
Most manufacturers of infrared thermometers offer some form of warranty or returns policy with the sale of their products. As a general rule, the more expensive the model is and the more well-known, respected the manufacturer is, the more extensive the warranty and returns policy, however this is not always the case.
This is an important consideration because digital pyrometers are complex, calibrated pieces of technology and although they are generally sturdy and robust in terms of their build, they are sensitive pieces equipment.
With the increase in online distribution of goods and shopping, it is important to recognize that each infrared thermometer is likely to pass through multiple hands from the manufacturing floor until it reaches its final destination. There is always a risk of damage resulting to the unit which is outside the control of the manufacturer.
Many reputable third party resellers online offer a great returns policy in addition to the manufacturer’s warranty and it is recommended that any prospective buyer checks the relevant warranty or returns policy prior to purchase.
As mentioned previously, every object whose temperature is above absolute zero (-273.15°C / -459.67°F) emits infrared energy. But not all objects emit infrared energy equally. Emissivity refers to the efficiency with which a material emits or absorbs infrared energy. All values of emissivity fall between 0.0 and 1.0. An emissivity value of 1.0 is referred to as a ‘perfect emitter’ because it radiates 100% of the energy. An object with an emissivity value of 0.0 emits no infrared energy at all. As a general rule, materials which are highly reflective or shiny have a low emissivity and those that are darker colored and dull have a high emissivity.
In order to measure the true surface temperature of a surface with a digital pyrometer, the object’s emissivity must be taken into account. To adjust for the specific object being measured, infrared thermometers must therefore have an emissivity setting. The emissivity of a material is influenced by a number of factors and is generally grouped as follows:
- transparent objects
It is important to note that the emissivity of metals can change over time as a result of general wear and tear, oxidation or soiling, however so long as surfaces are not shiny, metals can be measured quite accurately in most cases. Non-metal groups include organic materials, such as wood or paper, food items and ceramics. Transparent objects include items like glass.
Infrared thermometers either have a fixed emissivity of either 0.95 or 0.97, or they have adjustable emissivity which allows users to manually adjust the level to take into account the different type of surfaces they may need to measure.
The consequence of measuring temperature from a surface which has a different emissivity to that which a wireless thermometer measures is that the readings will not be accurate.
A fixed emissivity of around 0.95 does allow for accurate and reliable temperature measurements to be taken from the vast majority of surfaces, however for those who require their unit to measure surfaces which include reflective or shiny objects, then an infrared thermometer which allows for adjustable emissivity is worth serious consideration.
Infrared Thermometer Applications
Thermometers have been used as a measuring device for temperature for centuries and the invention of infrared thermometers has allowed users to be able to take accurate and reliable measurements of surface temperatures without requiring direct contact with an object.
After time, temperature is the second most frequently measured physical unit and various fields depend heavily on accurate temperature measurements as an important indicator of product quality or equipment conditions. Technological innovation and efficient mass production techniques in recent years have seen a decrease in the cost of infrared thermometers and an increase in their reliability. This in turn has seen an increase in new applications for these diagnostic instruments.
Professional and general applications for wireless digital thermometers are limitless only by the imagination and the following is a summary of the more common uses of these devices.
One of the primary advantages of an wireless thermometer in professional applications is the time and cost efficiencies that can be achieved by:
- performing diagnostics quickly without the need to shut down systems
- preventing equipment malfunction
- compliance with industry or regulatory requirements.
- obtaining non-invasive temperature measurements
The following is far from an exhaustive list, but a quick summary of some of the more common uses of an infrared thermometer by professionals.
- conduct energy audits to determine leaks or infiltration
- scanning ductwork for air leaks or discovering issues with insulation
- monitor equipment, pipes, radiant heating and live electrical circuits for faults and to confirm they are operating within designed parameters
- verify manufacturing processes are operating efficiently
- ensure product quality via monitoring of equipment temperatures
- monitoring high temperature substances (plastic, metals etc) and moving targets such as those on a conveyor belt.
- applying HACCP procedures to ensure food quality and safety.
- Monitoring temperature at various critical control points when goods are received, stored, cooked, served, cooled or reheated.
- prevent cross-contamination
- monitoring electrical systems and circuit boards to predict potential equipment failure and diagnose problems
- measuring electrical components, electric motors and motor bearings to ensure proper operating temperatures
- checking transformers and power circuits detect hot spots and ensure power balance.
- diagnose overheating by testing thermostat and radiators for clogs
- troubleshooting poor A/C cooling performance and engine misfires
- checking bearings, catalytic converters and brake temperatures to diagnose overheating or pulling and tire temperatures for loading
- measuring body temperature to check for fever and illness
- Fire Safety
- detecting hot spots in building surfaces and floors during and after a fire
Many of the professional applications of digital thermometers can be of equal benefit to the general consumer and within the home.
It is important to remember that infrared thermometers only measure surface temperatures and not internal temperature. So for some popular applications in and around the home, they will provide only a very general guide of internal temperature if that is the intended purpose. Their increasing popularity for such applications lies with in their ability to measure temperature quickly and without making a mess.
They are an ideal tool for:
- checking windows and door frames for leaks
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- checking a home’s insulation for leaks/deficiencies
- ensuring furnaces and air conditioners are operating properly
- many of the automotive applications used by professionals as listed above
- checking temperature of refrigerators, freezers, pots and pans on the stove
- hobbyists when:
- tuning gas-powered engines in model race cars and airplanes
- making soap and candles – to get the surface temperature of lye and oils and hot wax
- brewing home beer – pitching yeast when making a homebrew beer
- bread making – proofing yeast in bread
- preventing contact burns for children playing on playground equipment or leather car seats
- obtaining non-intrusive temperature readings of humans, pet reptiles and amphibians
- checking the surface temperatures of food and exterior of drink containers (bottle, glasses etc) holding hot liquids. This is especially handy for parents with young children.
The above list is a sample of some of the cool uses of an infrared thermometer in and around the home. Their application is limited only by the imagination and they are an invaluable device for every home. Digital pyrometers are easy to operate and now that they are more affordable, there really are no excuses for every family to enjoy the benefits and efficiencies they can provide.
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