The Fluke 570 Series of infrared thermometers meets the needs of maintenance professionals who want to make accurate temperature measurements at a distance.
This application note describes the Fluke 570 Series, the most advanced infrared (IR) thermometers available, and how to put their features to work in today's plants and facilities. In order to explain the capabilities of these thermometers, this note also explains some of the basics of IR thermometry.
Features professionals need
Ask experienced maintenance professionals what features they want most in an infrared non-contact thermometer, and the list would surely include accuracy. While some models are accurate to only ±1% (or more) of reading, models in the Fluke 570 Series are accurate to ±0.75% of reading. Other features important to maintenance pros include:
High optical resolution. Maintenance professionals want their IR thermometers to provide accurate temperature readings at some distance, as well as close up. For example, it's 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 feet above the floor the next minute.
The optical systems of all IR thermometers collect infrared energy from a circular area or "spot" created by the infrared beam. The farther from the instrument one gets, the larger the spot is. The 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 (distance-to-spot, or D:S ratio) at its focus point; for other distances, this ratio is a useful approximation.
Some low-end or entry-level instruments have a relatively low D:S ratio of 6:1 or 8:1. So, to measure a one-inch spot, the user must be six or eight inches from the target. The Fluke 570 Series has a distance-to-spot ratio of 60:1. This means they can measure the same one-inch spot from a distance of approximately five feet. Remember, from five feet away, the entry-level instrument would be measuring a spot seven and a half to ten inches in diameter.
Optical resolution is important in IR 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 could not record the temperature of the conveyor motor described earlier using the instrument with a 8:1 D:S ratio. However, it is likely that she or he could get the job done with a Fluke 570 Series instrument with a 60:1 resolution. High resolution is also important when working closer up because it allows precise measurement of smaller targets from a safe distance.
Laser sighting. Many models of IR thermometers have a laser beam for sighting a target, but a single beam in the middle of a spot only tells the user where the center of the spot is. Fluke 570 Series units have a three-dot sighting system that reveals to the user not only where the center of the spot is but where its edge is. So, the technician measuring the temperature of the aforementioned conveyor motor will know if the entire IR spot is on the target (motor housing). The Fluke 570 Series laser sighting also features a special laser that appears twice as bright to the human eye (while maintaining the same safety rating as less bright lasers), making accurate sighting easier in a variety of lighting conditions and distances.
Wide temperature range. Maintenance pros want instruments that will measure a wide range of temperatures. They may have to track the temperatures of refrigeration coils one day and check the oil level in a transformer the next. Also, in some manufacturing settings, production personnel use handheld IR thermometers to monitor very hot products such as hot steel or plastic. Thermometers in the Fluke 570 Series measure from -30°C to 900°C (-25°F to 1600°F), a large range that provides many uses in process quality control.
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 materials of that object is known to emit that energy - its emissivity. Since the emissivity of most organic materials and painted or oxidized surfaces is 0.95, many IR thermometers use this factor in all temperature calculations. However, certain materials, such as concrete and shiny metals, are poor emitters, so using an emissivity setting of 0.95 in calculating surface temperatures of these objects will not yield an accurate result. Users of thermometers in the Fluke 570 Series can adjust the emissivity setting of their instruments. This feature makes readings more accurate, and it, like the high temperature range, allows these units to be used extensively in process quality assurance.
Speed. A thermometer that records readings quickly will record accurate readings even in situations where target temperatures are changing rapidly. High response times by thermometers mean that serious problems can be diagnosed immediately. Furthermore, there is no need to shut down a process to take a reading. The Fluke 570 Series has a very fast 250 mSec response time.
All of the features of Fluke 570 Series mentioned so far are available on all units. In addition, all have backlit liquid crystal displays for viewing in poorly lit areas and the capability to store the last 10 readings and display them on a bar graph for easy comparison of readings. Each also has a high alarm warning that is both audible and visible, making it effective even in loud plants. In addition, each can be ordered as a close-focus unit with a 50:1 distance-to-spot ratio. This latter option is especially useful for close-up troubleshooting of electrical circuits in which targets tend to be relatively small, since it has a minimum measurement spot size of 0.24" (6mm).
The power of data logging
When a user holds a Fluke 572 thermometer, all of the aforementioned capabilities are literally at his or her fingertips, but a move to the Fluke 574 adds the power of 100-point data logging. With this capability plus software for logging, graphing and analyzing temperature data on a PC and an RS232 connection to move the data from the thermometer to the PC, the time once used to transcribe data is minimized. Furthermore, analysis is streamlined. Reports get written faster and more accurately, and needed repairs are more likely to happen before equipment fails.
Along with their inherent data logging capability, the more advanced members (Fluke 574 and 576) of the Fluke 570 Series have easily accessible pre-set emissivity settings for common materials. Using this feature, when appropriate, saves the user time in not having to look up the proper emissivity setting before taking a reading. Also, these advanced models have customizable features such as log names, high and low alarms, emissivity values for special conditions, etc. A technician can customize an instrument to conform to his or her inspection route.
To all of this, the Fluke 576 adds digital photography capabilities and a USB connection (instead of RS232) for PC hookups. When a temperature reading is recorded, the instrument records the temperature on the photo of the target along with the date and time of the measurement. Having photographic documentation of measurement is a powerful documentation and reporting tool.
Walking a route
Let's return to the electrical panel mentioned earlier and imagine checking its temperature with the Fluke 576 as part of a predictive maintenance route. To begin with, using the camera's focus ring, the technician will focus the camera on the part of the panel to be measured. If the area is dark, the thermometer will automatically illuminate the area with a built-in flash. With the thermometer in "log mode," the technician will pull and release the trigger. Having recorded the temperature and image, the camera then automatically prepares to record the next temperature and image on the route.
At the end of the route, the technician uploads the collected data and images to a PC. At this point, the technician has several options. The data and photo from the electrical panel can be compared to data and photos recorded earlier. Questions can be asked and answered: Was the inspection done properly? Was this measurement consistent with earlier ones in terms of location and temperature recorded? Is the panel's temperature trending upward?
The technician can record the electrical panel's data in tabular view with photos beside temperature data; tailor high or low alarms to this location; view the panel's minimum, maximum and average temperatures; graph the data to reveal trends and more. If warranted, a report on the status of the electrical panel can be created with photos for added impact or to help guide repair personnel to the location. Then, the report may be distributed electronically or printed for physical distribution or even posted on a company's intranet.
Temperature measurement strategies
In general, there are three ways to use any kind of infrared, non-contact thermometer:
Throughout the preceding discussion, various suggestions have been made for using infrared thermometry for plant predictive and preventive maintenance, electrical applications, process monitoring, quality assurance and other applications. Special mention should be made here of hazardous environments where the presence of flammable gasses or vapors make operating most electrical devices very dangerous. A model of the Fluke 574 has been tested by Factory Mutual, a US organization, and has received a nonincendive (Class I, Division 2) approval. Check that this approval is appropriate for your application and is accepted in your country. Be aware that the nonincendive model is not available with the close-focus option.
For industries where calibration is a matter of concern, units are available with a NIST calibration certificate. In addition, here are some additional suggestions for areas where an IR non-contact thermometer will prove useful:
Electrical Maintenance. Check for heat buildup created by loose connectors. Troubleshoot problems in battery banks and power panel terminations, ballasts, switch gear and fuse connections. Identify hot spots in the output filters on DC battery connections.
Equipment Maintenance. Check moving parts in motors and gearboxes 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.
Building Controls. Monitor HVAC/R components for quick energy audits and room balancing in a short time. A 60:1 distance-to-spot ratio makes elevated vents and returns very accessible.
Process/Product. Monitor process lines. Check the temperature of different products on production lines. They can vary from rubber tires to plastic, from cellophane wrapping to chocolate bars.