A Closer Look at Diagnostic Technology
By James Piper - September 2005 - Equipment Rental & Tools
Preventive maintenance has long been recognized as the key to efficient and reliable operations. While computerized maintenance management systems have assisted engineering and maintenance in developing these programs, maintenance personnel have frequently lacked the needed tools for effective implementation.
Today, that situation has changed, thanks to the development of a range of handheld diagnostic and monitoring equipment that is relatively inexpensive and easy to use.
Increased demands for indoor air quality (IAQ) have resulted in the need for engineering and maintenance to more closely monitor and document conditions within buildings. While centralized automation systems can give an overall indication of conditions within a building, most IAQ problems tend to be localized. Identification and resolution of these problems frequently requires the use of monitoring equipment to identify the problem is its location.
The latest generation of portable IAQ monitors allows users to take a range of measurements, including carbon monoxide, carbon dioxide, relative humidity and temperature. The monitors also can record particle counts, measure volatile organic compounds, determine airflow, and measure differential pressure. Users can collect data and read directly from the unit, or they can upload it to a desktop computer for further tracking and analysis.
One of the easiest to use and most valuable monitoring tools is the non-contact temperature monitor. Technicians can use these units to identify temperature variations in equipment, electrical systems, heat transfer surfaces, and structures. Some units also can produce a digital readout or a thermal image.
Technicians can use both the temperature monitor and the thermal imaging unit to detect a number of developing maintenance problems. The can clearly identify loose, dirty and corroded connections as hot spots, either in the image or the temperature reading. Worn bearings in motors also show up as hot spots. Dirty or plugged areas in heat transfer surfaces show up as unusually hot or cold areas. By identifying these developing problems, maintenance personnel can take corrective action before the problems result in costly equipment failures.
Power Quality Monitoring
As the number of electronic and computer-based systems installed in and used to operate facilities has increased, so has the need for high quality, stable power. Problems such as sags, spikes, transients and harmonics can easily disrupt the operation of this equipment.
In the past, it was difficult and expensive to track down the causes of these problems. Today, portable monitoring equipment has improved to the point where it can be effectively used to measure and log current, voltage, power factor and energy, while watching for voltage transients and other power related problems. The units record each occurrence, making the data available for maintenance personnel to help identify the cause of the problem.
Units offer cycle-by-cycle power analysis. Their ability to identify transients depends on their sampling rate, with the more sensitive units offering up to 512 samples per cycle. Most units offer eight sampling channels — four for voltage, four for current. Built-in memory allows users to collect and store data over an extended period. Standard interfaces allow users to upload data to desktop computers for analysis and long-term storage.
Electrical Motor Testing
The cost of system downtime has resulted in the need to identify developing electrical problems in motors before failures occur. While test equipment for motors has been available for years, only recently have advances in computerization resulted in lower costs and greater capabilities.
Today, equipment is available for both energized and de-energized testing to evaluate motor condition of motors. By performing these tests, technicians can identify developing problems and schedule service outages or install replacement units before a failure occurs and interrupts service.
Managers have a wide range of test equipment for motor testing from which to choose, depending on the application. Handheld, infrared temperature sensors and thermal imaging devices can help identify bearings that are overheating and loose electrical connections. Technicians can use portable vibration analyzers to identify misaligned motor drives, loose or worn couplings, and worn bearings.
At the high end of the motor test equipment range are portable motor analyzers. These units perform a range of electrical tests, including surge, polarization index, DC HiPot, megohm, and winding resistance. Most of these tests come preprogrammed, allowing easier operation in the field.
Technicians can upload data collected from the tests to a desktop computer, where they can store and used it to generate predictive maintenance reports. Then, they can combine results from successive tests to produce trending reports — a valuable indicator of motor condition and essential in projecting remaining service life.
For managers in facilities with central chillers, boilers and large heat exchangers, it can be difficult to determine the condition of internal tubes in the generation of hot or chilled water. While annual inspection and cleaning can keep the tubes clean for maximum efficiency, the level of wear is much difficult to determine. Managers can contract with specialized testing companies to perform necessary tests, but tests must be scheduled and tend to be rather expensive.
Advances in corrosion test equipment has resulted in equipment that is both easier to use and lower in cost than pervious models. Eddy-current testers use an inspection probe that is inserted into each of the tubes of the device being evaluated. As the probe passes down the length of the tube, any changes in the thickness of the tube — due to erosion, corrosion or pitting — produce changes in current in the probe that technicians can use to identify the location and extent of the damage to the tube. Subsequent inspections can help identify the rate of deterioration. By identifying the location and the extent of the deterioration, the equipment can help maintenance personnel determine when to schedule overhauls.
While eddy-current testers are useful in identifying defects in heat-transfer tubes, they do not work well on tubes made with highly permeable alloys, such as carbon steel. The magnetic properties of these alloys prevent the penetration of the magnetic field into the metal, limiting the detection of both surface and sub-surface defects. Instead, technicians can use a portable magnetic flux leakage detector.
James Piper, P.E., a national consultant based in Bowie, Md., has more than 25 years of experience in facilities maintenance and engineering management.