Uptime Magazine - October/November 2008 - (Page 34)

at a smelter or a furnace—but can also be used for cold-processing at a dairy. Consider your application, and then check to make sure that the camera can accurately measure within your application’s temperature range. an object which is 50° C and another object which is 50.1° C. The industry standard for measurement is the second half of this equation — “@30°C.” This means that when this test was performed, the camera temperature itself was at Most specifications refer to this 30°C. Most camera manufacturas the “temperature range” or ers will use the @30°C in their “temperature measurement caspecification sheet. Beware, if pability.” Think about the maxithe “@30°C” is not included, mum and minimum temperature then you don’t know at which that your targets could become, and conditions this camera was then insure that these temperatures are tested and you cannot well within the camera’s range. Many fairly compare this to IR cameras have the ability to have two another camera or more range settings. Just be sure that which has been your required temperatures fall within tested @30°C. these range settings and are not an “add-on” Think about the option you must purchase. temperature of the objects Taking the Mystery Out you are going of Camera Specifications Figure 1 - Example of a camera with an to measure. Are LCD display only. Typically, these cam- you looking for extremely small While looking at various camera eras are better suited for indoor use. changes in temspecifications, you will notice peratures, or camera manufacturers use different terminology to express the same con- larger changes in temperature? cept. To further confuse the issue, manufacturers will also use different units of measure. Temperature Resolution/Accuracy – Example: This is frustrating for the new thermographer. +/- 2°C or 2% of reading However, by reading this article, and by exTemperature resolution or temperature acamining many camera specification sheets, curacy refers to the level of accuracy of the you will become adept at “de-coding” camera temperature measurements being recorded specifications. Following are five areas that by the camera. often feature confusing terminology and units of measure. In this example, +/- 2°C indicates that the reThermal Resolution/Sensitivity – Example: 0.1°C @ 30°C Remember that infrared technology uses variances in temperature to define an image. Simply put, if two objects are the same temperature, when you look through the camera, you will see the two objects as one object. The simplest way to describe thermal resolution is by asking the question, “If you have two objects at different temperatures, how close in temperature can the two objects become, and yet the camera will still measure and ‘see’ these differences?” Thermal resolution or thermal sensitivity is the answer to this question. Our example specification above shows 0.1° C. This means that the camera can detect temperature differences between two objects which are only 0.1° C apart. An IR camera with this sensitivity can detect differences between corded temperatures are accurate within 2 degrees C. Therefore, if you get a temperature reading of 50 degrees, the object is actually 48°C - 52°C. When imaging objects at higher temperatures, extreme temperature accuracy may or may not be critical. However, small temperature differences are extremely important in the medical field. Almost all industrial-use camera specification sheets use the +/- 2°C. The “or 2%” part of this equation refers to those objects which are greater than 100° C. For temperatures under 100° C, use the +/2°C. For objects greater than 100°C, expect a temperature variance of up to 2%. Detector Types – An infrared camera measures the variances in heat or heat energy to create an image. A regular camera measures the differences in light or light energy to create an image. In an infrared camera, there are a series of highly heat-sensitive detectors or elements inside the camera that pick up and record temperature differences. This information is converted into an image by a small computer inside your camera. The more individual detector elements you have, the clearer the image will be. Just like a computer monitor or digital camera, we sometimes refer to these detector elements as pixels. A camera with a detector array of 320 x 240 means that there are 320 x 240 = 76,800 individual detector elements (or pixels) embedded on the detector array. A camera with 120 x 160 means that there are 19,200 (120 x 160 = 19,200) detector elements embedded on the detector array. Ask yourself, “How much image quality do I actually require?” It may be that the lower resolution is perfectly fine for your applications. Look at your budget and try several cameras of various resolutions to see which will work for your application. Of course, we all would like to drive to work in a Jaguar, but we can still get there driving a Taurus! In addition, there are other factors besides the number of pixels which determine the final quality of the image—such as the lens and processor. The only sure-fire way to find out if the image quality is sufficient for you is to try the camera for yourself. Caution: some camera specification sheets will say 320 x 240, but if you look carefully, you Figure 2 - Example of a camera with both an eyepiece and an LCD display. These types of cameras are more versatile. october/november 2008 34

Table of Contents Feed for the Digital Edition of Uptime Magazine - October/November 2008

Uptime Magazine - October/November 2008 Contents Upfront Upclose: An Asset Management Oasis in the Desert Information Technology: Streamlining Through Simplicity Lubrication: Phases for Framing a Solid Foundation Infrared: Do Your Homework Before You Buy Maintenance Management: Get It Together by Getting Together Motor Testing: Key Elements in Motor Decision Making Precision Maintenance: Shedding Some Light on Tolerances Reliability: RCM & the Mortgage Meltdown Ultrasound: A Multidimensional Tool Vibration: The Whirling Pump Mystery, Solved with ODS Upgrade: Are You Looking in the Right Place for Your Wear Debris?

Uptime Magazine - October/November 2008

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