PREDICTIVE MAINTENANCE & CONDITION MONITORING FEATURE The measurement of vibration can provide valuable information on the health of
machinery, allowing maintenance to be carried out when it is needed rather than at fixed intervals. Monitran’s managing director, Andy Anthony, gives an overview of some of today’s condition monitoring equipment and some recent applications
W
hile machinery downtime is expensive, if it is unexpected it is
especially so. It is, however, possible to get an insight as to whether problems are brewing by analysing the vibration of machinery in operation. As an example, accelerometers can be used in bearing analysis of rotating machinery such as pumps and compressors, and in heavy industry such as paper and steel mills. Velocity sensors, meanwhile, are ideal for continuously monitoring complete assemblies such as fans, gearboxes and air-handling units. The decision of whether to use a velocity transducer or accelerometer depends on factors such as the required frequency response, sensitivity to noise, temperature range, etc. While velocity sensors are generally used for low to medium frequency measurements, accelerometers have greater sensitivity to high frequency vibrations and can operate across a greater temperature range.
SENSOR SOLUTIONS An abrupt change in vibration can indicate a fault such as machinery working loose from its mountings, a fan blade malfunction or a bearing failure – meaning immediate attention is needed. Changes in vibration occurring over time can indicate gradual wear and the coming need for maintenance. One sensor developed for use in condition monitoring is the new MTN/1330 triaxial accelerometer from Monitran, which was designed to meet customer demand for a sensibly priced, low profile triaxial sensor. This measures acceleration simultaneously in all three spatial axes and is intended for general purpose vibration measurement. The constant current device has three isolated AC outputs corresponding to the X, Y and Z axes, and a top-entry four-pin M12 connector. Standard sensitivity is 100mV/g at 80Hz, and the acceleration range is ±80g. With this, the internal electronics
are isolated to minimise noise, with increased bias voltage stability. In addition, the case is sealed to IP66 and is available in stainless steel, or aluminium for reduced weight. Among the advantages of using triaxial rather than single axis sensors are reduced data collection times, a reduction in wiring and more consistent reliability in readings. Sensors can be used individually or as part of a condition monitoring system
Checking the pulse...
...of your machinery
such as Monitran’s MTN/5000, a microcontroller-based system that can be used for monitoring and logging vibration as well as other types of sensor input, such as temperature. With an easy-to-navigate touch screen, it enables users to set thresholds for up to 96 alarms individually or across all channels, as well as for data sampling periods, ranges and accuracy levels. AC outputs are available via door-
mounted BNCs for analysis, while Modbus and remote PC monitoring are available as options.
ON-BOARD SYSTEMS The MTN/5000 condition monitoring system has recently been used for a vibration monitoring system on a new hovercraft. By having continuous, on- board condition monitoring, if a drivetrain component were to fail then an alarm can be raised to immediately warn the pilot. In addition, the constant monitoring of key components meant it was possible to save weight by using less rugged components, with consequent fuel savings. The on-shore maintenance team, which has access to real-time data, can also be notified, allowing them to commence preparations before the hovercraft even lands and therefore provide the quickest possible return to service. The hovercraft’s twin drivetrains
were each fitted with 12 Monitran accelerometers. These stainless steel bodied sensors were sealed to IP68, with integral LSZH-coated screened cables which were fed into a bulkhead- mounted waterproof MTN/5000 condition monitoring system housing 28 signal conditioning units. Each signal conditioning unit feeds its
/ INSTRUMENTATION
The MTN/1330 triaxial accelerometer measures acceleration simultaneously in all three spatial axes
output into a microcontroller with, in this instance, the capacity to handle another four channels if need be. The raw AC signals, i.e. the 0 to 100mV outputs of each accelerometer, are also made available via BNC connectors, allowing an oscilloscope or spectrum analyser to be connected. Of additional benefit, the condition
monitoring unit also connects using the Modbus communications protocol to a transmitter which sends data to a shore-based remote monitoring system.
LARGE SCALE SYSTEMS Another application is a recently upgraded portside coal handling facility in the north of England. Here, the site’s conveyer belts, stacker-reclaimer machines and a variety of ancillary hoppers and mechanical buckets have to remain operational 24 hours a day. So, over 200 vibration sensors are being used to monitor the health of motors, gearboxes, drivetrains and fans. These are connected via multicore cable to 17 MTN/5000 condition monitoring systems, which also receive digital data from oil quality sensors. The facility also has a ship-to-rail
Monitran’s cost-effective and versatile MTN/5000 condition monitoring system can be used for monitoring and logging vibration and other types of sensor input, including temperature
line for biomass fuel, whose motors, gearboxes, drives and fans are also protected by a hardwired conditioning monitoring system. As in the coal handling area, the sensors are connected to junction boxes, from where multicore cables take the signals to two motor control centres, one port side and one rail side. Each centre has a purpose-built
condition monitoring system using the MTN/5000 for monitoring and logging data. Information from both systems is fed onto the site’s SCADA network. Although the motor control centres are not classified as ATEX II zones, consideration had to be given to the fact that both condition monitoring systems are electrically connected to sensors which are in a hazardous environment. Zener barriers were therefore used, one each per channel, to suppress any voltages that could cause a spark.
Monitran T: 01494 816569
www.monitran.com
INSTRUMENTATION | OCTOBER 2016 17
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