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The Squeaky Wheel Gets the Repair

In our chat session last month, one of the topics that came up really caught my attention — probably because of my work in the industrial environment and as a railroad maintenance-of-way worker. It concerned preventative maintenance on rotating equipment.

This generally means detecting problems in motors. The problem areas are primarily the bearings and, secondarily, motor winding overheating. If you monitor the motor temperature — and probably motor winding current, voltage, and phase angle while you're at it — you can detect problems well before they become catastrophic. If you listen to the bearings with a MEMS (micro-electro-mechanical system) sensor, you will be able to detect vibration that portends bearing failure.

In consideration of just these few sensor and data acquisition functions, it's obvious there is a lot of functionality here. It should be combined and integrated. An integrated analog approach is needed that will accept these inputs:

  • Voltage, phase A
  • Voltage, phase B
  • Voltage, phase C
  • Current, phase A
  • Current, phase B
  • Current, phase C
  • Multiple temperature sensors — assume a minimum of 3
  • Multiple MEMS vibration sensors — assume a minimum of 2

But there is another important function we've left out. What do you do with the information from all these sensors? Certainly you will digitize and multiplex it — but then what? How do you get it to the PLC (programmable logic controller) that is running the motor? You could run a data cable next to the three-phase power cables that are already routed between the motor and the PLC. Even though the wire ways or conduit are present, clearly that method is fraught with peril.

In the case of monitoring bearings in a gearbox or on a conveyer belt, there probably is no easy method for data cable routing. Running such cable, materials and labor become a significant cost in factory installations. And conveyer belts are notorious for static electrical charge accumulation (think of a Van de Graaff generator), which can damage sensitive circuitry.

A sensible approach to work around these problems would be to use a low-power RF data transfer link such as Bluetooth. Not only will this approach help with the problems described above, but it should be possible to integrate the functionality with the sensor circuitry.

Besides use in the industrial environment, this same integrated analog functionality can be used to monitor railroad rolling stock. In some versions of this, MEMS and temperature sensors could be installed on the trucks of all rolling stock to send information to the engineer or to wayside monitoring equipment. In other versions, MEMS sensors could be installed on the rail web to listen for wheels with flat spots. Flat spots develop when emergency braking occurs. The flat spots pound away at the railhead, damaging it and further degrading the wheels.

The railroads are already using some technology to detect problems:

  • BNSF has provided some information on technologies they are pursuing.
  • LBFoster/Salient Systems is building some interesting trackside products that can detect bad bearings, flat spots, and hunting trucks.
  • Another member of the UBM family, Design News, published this article last November that describes in more detail how bad bearings are detected.

I may build up a strain gauge bridge circuit + amplifier and glue the strain gauge to the web on a section of rail on some nearby tracks and listen to the amplifier output with headphones. It should be interesting to see what it sounds like.

The task now is to move the existing technology onto an IC so that power consumption and cost can be reduced. All of the preventative maintenance methods would benefit. And there should be plenty of opportunity to sell the technology — the market looks to be huge.

Have you had any experience with this sort of preventive maintenance technology?

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