A particular production line is generating more than its share of trouble calls. The line supervisor has put in several work requests to correct “motor speed deviation,” “inconsistent motor speed,” and “main drive motor speed fluctuation problems.” He recently complained to his production superintendant about “maintenance incompetence” in “fixing the motor.” The production superintendant asked the plant engineer to look into it.
The plant engineer called you into his office and outlined the complaint. Then he pointed out that the production supervisor isn’t a technical person and is probably not describing the correct problem. He’s asked you to resolve the speed variations with that line and also smooth over ruffled feathers.
What should be your approach?
Answer to quiz. The plant engineer has made an accurate assessment. A motor’s speed is determined by the number of poles and the frequency of the power supply, along with the amount of load and slip. This means that the motor itself (unconnected to any load) isn’t going to vary its speed. In the typical 60-Hz system, the synchronous speed of an 8-pole motor is 900 RPM, and this does not vary. But with load and slip, it will run at a lower RPM. If the load varies, so will the speed.
If the work analyst (or whoever writes the work orders) isn’t particularly familiar with motor applications and receives a work request that seems to be saying the motor is defective, that person will probably write a work order that is limited to the motor. Check for vibration, perform insulation resistance testing, check isolated motor speed with a tach, and lubricate the motor. Of course, the motor can return “All Good” per these tests, and the actual problem isn’t even looked at. That is probably what’s occurring here.
This illustrates a classical troubleshooting mistake, which is that of characterizing a system problem as a component problem. It is far too easy to focus on the wrong component, and this approach also ignores connections between components.
Begin solving this by sketching out the system. It will consist of four major areas:
- Power supply
- Control elements
- Input sensors
- Control system
You solve any system problem in the order above. So that means you always start with the power supply. In this particular case, it is an unlikely culprit but this is where you start. Problems here can cause “mysterious” problems elsewhere.
Next, look at the control elements. This motor is one of them. Does it have an electronic drive? What about a gear box? Is there any kind of coupling that can create variations? What other control elements are possibly affecting process speed? For example, is there an automatic brake that is partially engaging on a random basis?
Input sensors themselves can be bad, but input sensor wiring may be compromised by routing errors and subject to induced voltages from power wiring. So be sure to measure the actual voltage on any sensor cables (at the input terminals of the controller is a good place).
The control system may be a panel of switches, a PLC, or a DCS. The variable frequency drive for a motor is also a type of control system. The programming of these doesn’t go bad, so if they used to work and the programming hasn’t changed then don’t look at the programming unless there has been some kind of system reconfiguration or process change.
In checking each of these areas, you include checking the incoming and outgoing connections between components. And check for conformance with bonding requirements, as bonding errors can cause all kinds of problems.
There’s a fifth area that many people will look at first. That is the area of human error. What are the operators doing that may be causing the problem? In this case, for example, are they causing variations in load by the way they are feeding in material? It is possible to jump right to the actual problem this way. But you have to always keep in mind that maintenance is as much a political function as it is a technical one. Before you point fingers, rule out technical causes. And when you do identify human error, part of doing so diplomatically is being able to show you’ve corrected for or ruled out other causes.
The plant engineer has two problems to solve, and the remaining one is the issue of ruffled feathers. The production superintendant probably cares only that the technical problem has been solved so that neither quality nor output will fall below desired levels. The line supervisor is the one whose feathers are ruffled.
You could blame him for poor communication, but he could respond that it’s up to your department to figure out the cause. So turn that dynamic around. First apologize for the poor service, and be sincere about it. If he responds graciously, thank him for his understanding. Then say something like, “You know, there is a way to reduce the chances of such a Keystone Kops performance in the future. Care to know what that is?”
Then say that the confusion at maintenance was people there confused a system problem with a component problem. Don’t say that the maintenance supervisor erred by misdirecting them into doing so. Just say something like, “Now that you know people can fall into that kind of trap, you can help them avoid it by guiding them towards looking at the overall system and working their way down from there.”
Now he has been apologized to, hasn’t been accused of doing anything wrong, has been treated as if his guidance is worthwhile and sought after, and has been given the core idea of how to communicate a problem. This is the diplomatic way, and it serves maintenance much better than playing the blame game or even appearing to play it.
What if you had discovered operator error, for example operators were tossing heavy parts onto a conveyor instead of gently setting them on there using the mechanical lift? So again, you use diplomacy. The supervisor may not have seen this behavior before, because (as is commonly done with safety glasses non-compliance), they see him coming and do the work correctly. You can ask him something like, “If one of my guys tossed the parts up there without using the mechanical arm, wouldn’t that cause speed deviations?” Of course, he would say. That’s when you pull out your phone and start the video showing one of his people doing exactly that.
