Test and Measurement Solutions within Motion Control
Keeping the production line or plant running is critical to any business, as any unplanned downtime, lost productivity or delays can be very costly to the business, so having a preventative maintenance program, whether it’s electrical or mechanical is essential to keeping your systems operational, but it also helps to ensure the equipment is running efficiently and to its optimal performance levels. Let us look at a few areas within motion control, where Fluke test and measurement products can be used within the preventative maintenance program to prevent failure and also ensure the system is running at optimum performance:
Vibration – The benefits of screeningVibration is one of the earliest indicators of the machines health and can potentially identify problems before other symptoms appear (heat, sound, electrical consumptions), with more than half of unplanned downtime being caused by mechanical failures. The Fluke 805 (811-1397) vibration meter measures overall machine vibrations, bearing vibrations and temperature simultaneously, providing a four-level severity scale which assesses the urgency of problems for overall vibration and bearing condition as illustrated in the video below:
Measure and diagnose voltage unbalance in motors
Three-phase distribution systems often serve single-phase loads, however an unbalance in impedance or load distribution can contribute to unbalance of all phases, which can result in excess current flow in one or more of the phases and increased operating temperatures, that in turn can lead to the motor winding insulation breakdown and potential failure. Testing for unbalances can be achieved using the Fluke 435-II (752-5008) Three-Phase Power Quality Analyser.Motor Overload
Motor overload occurs when a motor is under excessive load, which results in excess current to be drawn, insufficient torque and also overheating, which will cause premature motor failure. The individual parts such as the bearings and motor windings may be working fine, but the overloaded motor will continue to run hot, but it’s important to begin troubleshooting for issues like conveyor failure/malfunction as around 30% of motor failures are caused by overloading. An ideal instrument for fault finding is the Fluke 289 (156-730) True-RMS DMM with data logging functionality in conjunction with a Fluke Clamp Meter I400 (520-2532) as you will be able to measure and log current to individual motor phases while the motor is still running under full load and compare that reading to the "Full Load Amps" from the motor’s nameplate and also check the current to each of the three legs of a three-phase motor to determine if there is single-phasing, a problem that occurs when there is a failure in one of the phases.
Encoders within a conveyor system
Encoders are commonly used to monitor and control the pace of conveyor belts and it’s often necessary to synchronise the motion of the conveyor with the processing station, so when problems arise it’s important the fault is accurately diagnosed. When a problem arises, for example, when the conveyor speeds up, we need to understand what is causing the problem - the encoder or controller? So the first step would be to measure the output of the encoder with a DMM, however, this doesn’t show you the full picture and doesn’t help locate the issue, but using an industrial oscilloscope like the Fluke ScopeMeter 120 Series (919-5065) the encoders digital output can be easily viewed as illustrated in the video below:
Variable Speed Drives (VSD)
Systems benefit through the inclusion of variable speed drives (VSD), which along with soft starts reduces the stress/impact on the motor at startup, but it also saves energy by controlling the speed of the motor and hence processes (see how to increase efficiency in a motion control system) but monitoring can be difficult as VSD’s generate pulses with fast-rising edges, that can create voltage reflections with the magnitude dependant on a number of factors including cable length, motor load, etc this can over time stress cables and the motor insulation, so testing of a VSD can be difficult as a DMM can show the peak voltages, but due to the pulse speed these readings can’t be relied on, so the use of an oscilloscope such as the Fluke ScopeMeter 120 Series (919-5065) can clearly show the signals as explained in the following video:
As well as this video, Fluke has produced an application note on measuring VSD’s using a Fluke ScopeMeter 190 Series (811-1230) which can be found as a download at the bottom of this article.
Harmonic distortion in motors
Harmonics are unwanted additional sources of high-frequency ac voltages or currents supplying energy to the motor windings, which in turn decrease the efficiency of the motor and increase the operating temperature. Often these harmonics are caused by VSD’s, and the IEEE standard 519-1992 defines the acceptable level of distortion for each harmonic. To inspect/measure for these, a power quality analyser is required such as, the Fluke 435-II (122-1786), which can measure the amplitudes of the harmonics and also log the data, ideally measuring over 24 hours monitors equipment during one complete plant cycle.
Testing for transient voltages in motors
Transient voltages are unwanted spikes or blips of voltage in an electric circuit that can materialise from sources from inside or outside of the plant (could be caused simply by loads being turned on or off0, these transients can cause insulation breakdown in motor windings and lead to early failure. The Fluke 435-II three-phase power quality analysers (122-1786) has a transient function, where the meter’s display can show voltages 50V above the normal voltage, i.e. the transient.
Throughout this article temperature is an overriding theme, but it’s not always possible to get close to the equipment to measure and inspect, so thermal imagery is still one of the easiest methods to identify thermal issues, but along with pinpointing the thermal issue the camera can record the readings so a service record can be maintained to early identify issues and the Fluke PRO Thermal Imager (175-2515) is the ideal choice, as the article Look Beyond The Pixel with Fluke details the advantages of image quality and this series of imagers.This article illustrates a number of test and measurement products Fluke has to monitor/identify potential issues within a motion control system and a summary of the products mentioned are: