Using temperature to detect the invisible

Temperature Measurement

March 2006 Temperature Measurement

Both preventive and predictive maintenance programs rely on regular inspections of the critical assets that comprise a plant or facility. These inspections range from visual inspections to non-destructive testing performed using a variety of instrumentation. While the methods vary, all inspections require plant personnel to periodically visit each of the systems, machines and/or equipment within the plant to anticipate the need for preventive and/or corrective maintenance.

Many maintenance engineers consider infrared non-contact thermometers and thermal imaging cameras not only indispensable for such inspections, but possibly the most important tools in their everyday work. By scanning surfaces with these temperature inspection tools, users can quickly locate hot and cold spots, which could be indications of underlying problems, and focus your maintenance efforts on exactly what needs repairing. Defective components are often classified according to the severity of the problem, which takes into account the absolute temperature of the component, the difference in temperature from the component to its environment, and/or the difference to other components in similar load situations. Thermal imaging cameras and handheld infrared thermometers provide a quick, safe and accurate way to collect this data. By comparing the results of inspections over time, changes in the temperature of objects can be detected and analysed to determine if failure is likely.

The paper and pulp industry is an ideal location for the use of thermal imaging equipment, a 5°C temperature difference is easily detected on an off-take roll and by moving back down the machine through the drying section the problem is easily located

Most mechanical systems generate some thermal energy during normal operation and temperature monitoring can evaluate their operating condition. One of the biggest problems in mechanical systems is excessive temperature. This excessive heat can be generated by friction, lubrication degradation, material or coolant loss or blockages. Regular temperature monitoring of machinery components enhances your ability to predict failure and plan corrective action before a costly shutdown, equipment damage, or personal injury occurs. Temperature checks should be performed regularly to locate hot spots or heat imbalances on, for example, drives and motors, bearings and transmissions, as well as hydraulic components, pumps, pulleys, and conveyors. Electrical equipment measurements have similar demands. Bus bars with loose or oxidised joints, for example, will rapidly exhibit higher than normal temperatures due to electrical resistance.

However, simply finding the heat does not necessarily mean that a problem is present. To properly evaluate the presence of hot spots, you need to know the operating load and acceptable heat ranges for those loads, which are specified by manufacturers of various equipment. In this case, you must be able to measure exact spot temperature values. Even a small temperature difference of 5 to 10° can mean a major problem. Normal inspection methods alone cannot always indicate such slight temperature variations. This is where infrared inspection enters the picture - knowing the precise temperature or temperature distribution is in some cases an absolute decision-making requirement.

With tools, such as handheld infrared thermometers, users can quickly and accurately measure small variations in surface temperature, taking into account all the variables of proper temperature measurement, such as emissivity and reflected temperature. When using thermal imagers users can make sound decisions about scheduling corrective maintenance activities and following up on repairs in the plant.

The latest generation of handheld infrared thermometers, like the unique PhotoTemp MX6 from Raytek, provide more than a temperature reading on a display, they include many features to support maintenance inspections. These include data logging, or the ability to capture and store temperature data from multiple locations along an inspection route, flexible display options such as maximum, minimum, average and differential temperature, audible HI and LOW alarms to indicate temperatures above and below acceptable ranges and Windows-based software for temperature trend analysis and report preparation on a PC. For enhanced documentation, the PhotoTemp is a photographic IR thermometer with a built-in digital camera. This variation allows the user to take snapshots of temperature measurements, showing the measurement spot marked by a laser, with temperature, time and date information. The detailed images can be easily downloaded from the unit, then included in inspection reports to document findings.

A good solution for maintenance is to use a thermal imaging camera that can provide simultaneous thermal imaging/spot temperature measurement and temperature analysis and reporting software. The latest thermal imager the ThermoView Ti30 from Raytek has all these features.

Maintenance is not the only area to use thermal imaging devices. Analysis of process problems is helped by thermal images of the offending process.

For more information contact R & C Instrumentation, 086 111 4217, [email protected], www.randci.co.za

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www:	www.randci.co.za
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Temperature Measurement

Using temperature to detect the invisible

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