Understanding infrared thermometers and using them properly in industrial applications goes a long way toward improving the process and product.2
An infrared thermometer and probe are used to monitor the fluid temperature of a soap bath solution used in the cleaning of raw wheels before the first primer process at Helios Coatings.
In a short time, hand-held infrared thermometers have gone from exotic to commonplace. Portable and convenient, they are useful for troubleshooting and checking both product quality and process quality. Following some best practices for process heating applications can help users get the most from these temperature measurement tools.
In general, there are three ways to use any kind of infrared, noncontact thermometer:
Measuring the Temperature at a Spot. This type of measurement is used to measure and track temperature at a single spot. It is useful for trending the temperature of an object or comparing a measurement to a specification. A thermometer with high repeatability helps ensure consistency for this kind of measurement.
Comparing the Temperature of Two Spots. This type of measurement might be used to check the functioning of a steam trap by measuring the temperature of the inlet and outlet. No change indicates the trap has failed open. A large change indicates the trap has failed closed.
- Scanning an Object and Detecting Changes within a Continuous Area. This capability allows the user to find hot or cold spots on housings, panels and structures. For example, one can check the heat sink of air-cooled transformers for cool tubes that indicate a restricted flow or a lack of flow.
Infrared thermometry can be used for process monitoring, plant predictive and preventive maintenance, electrical applications, quality assurance and other applications. Where calibration is a matter of concern, infrared thermometers are available with an NIST calibration certificate.
Applications and Features
The size of the temperature measurement area, or “spot,” increases with distance. Infrared thermometers with a higher distance-to-spot ratio (D:S) can take accurate measurements at a greater distances.Infrared noncontact thermometers have proven useful in many process applications.
Electrical Maintenance. Check for heat buildup created by loose connectors. Troubleshoot problems in battery banks and power panel terminations, ballasts, switchgear and fuse connections. Identify hot spots in the output filters on DC battery connections.
Equipment Maintenance. Check moving parts and housings in motors and gear boxes for hot spots. Temperature change can indicate developing problems in many types of equipment, from ovens and boilers to freezers. Routine temperature audits of generators and their bearings can prevent expensive repairs.
Measure Temperature of Process or Product. Monitor process lines. Check the temperature of different products on production lines. These can vary from rubber tires to plastic, from concrete to chocolate bars.
Building Controls. Although not a process use, a noncontact infrared thermometer also can be used to monitor HVAC/R components for quick energy audits and room balancing in a short time. An infrared thermometer with a 60:1 distance-to-spot ratio makes elevated vents and returns more accessible.
A worker monitors the surface temperature of a wheel that just had a primer coat applied in the spray booth in Helios Coatings research lab.
The following infrared measurement capabilities are particularly useful for measuring and tracking key indicators in industrial facilities.
High Optical Resolution. Industrial process technicians want their infrared thermometers to provide accurate temperature readings at some distance as well as close up. For example, it is not unusual for them to log the temperatures of connections inside an open electrical panel one minute and then want to take the temperature of a conveyor drive motor 20' above the floor the next minute.
The optical systems of all infrared thermometers collect infrared energy from a circular area or “spot,” which is illuminated by an infrared beam. (The infrared spot is for aiming purposes only, and not a part of the actual measurement process.) The farther from the instrument one gets, the larger the spot that is measured.
The optical resolution of an instrument is defined by the ratio of the distance from the instrument to the object, compared to the size of the spot as its focal point. This is commonly known as distance-to-spot, or D:S, ratio. For other distances, this ratio is a useful approximation.
Some entry level-instruments have a relatively low D:S ratio of 6:1 or 8:1. Better infrared thermometers for process uses have greater distance-to-spot ratios, going as high 60:1. For instance, with a 6:1 ratio, the user must be 6" from the target to measure a 1" spot. With a 60:1 ratio, you can measure the same 1" spot from a distance of approximately 5'. By contrast, from 5' away, the entry-level instrument would be measuring a spot 7.5 to 10" in diameter.
Optical resolution is important in infrared thermometry. In order to get a good reading, the target must be larger than the spot size and ideally should be twice as large. For example, from the floor, a technician might not be able to record the temperature of a conveyor motor described using an instrument with a 8:1 D:S ratio. However, a 60:1 resolution would get the job done. High optical resolution is also important when working closer up because it allows precise measurement of smaller targets from a safe distance.
Good Laser Sighting. Accurate aiming is critically important. Better quality infrared thermometers may have lasers that appear brighter to the human eye while maintaining the same safety rating as lasers that are not as bright. This makes accurate sighting easier in a range of lighting conditions and distances.
An infrared thermometer is used check the exit temperature of wheels after a metal primer coating is cured in a UV oven.
Wide Temperature Range. Process technicians must measure a range of temperatures. They may have to track the temperatures of refrigerated products one day and the temperature of baked goods emerging from the oven the next. In some manufacturing environments, production personnel use handheld infrared thermometers to monitor very hot products such as hot steel or plastic. Make sure that the infrared thermometer you plan to use has sufficient measurement range for the job. High quality infrared thermometers can measure from -25 to 1,600°F (-30 to 900°C).
Adjustable Emissivity. Infrared thermometers calculate the surface temperature of an object using the amount of energy emitted by the object, and the efficiency with which the surface material of that object is known to emit that energy - its emissivity. Because the emissivity of most organic materials and painted or oxidized surfaces is about 0.95, many infrared thermometers use this value for all temperature calculations. However, some materials such as concrete and metals are poor emitters, so using an emissivity setting of 0.95 in calculating surface temperatures of these objects does not give an accurate result.
Some infrared thermometers enable the user to adjust the emissivity setting of the instruments. This feature makes readings more accurate, and it, like the high temperature range, allows these units to be used in process quality assurance. Some units offer selectable emissivity settings for common materials.
High Measuring Speed. A thermometer that records readings quickly will record accurate readings even in situations where target temperatures are changing rapidly. Short response times of infrared thermometers mean that serious problems can be diagnosed even when temperatures are changing rapidly or require fast scanning. Furthermore, it is not necessary to shut down equipment to take a reading. Some infrared thermometers may have response times as fast as a quarter of a second.
Datalogging. Some infrared thermometers may enable the user to record many data points that can later be downloaded and analyzed with software for logging, graphing and analyzing temperature. This feature can save a lot of time and minimize transcription errors as well.
Other useful features include a lighted display makes it easier to view results in poorly lit areas. Also, high temperature alarm warnings call attention to temperatures that exceed a specified threshold. Alarms that are both audible and visible are more effective even in loud environments.