Viewpoint News, March 2010

Maintenance

by James Campbell - jac@viewpointusa.com

Last month, we discussed platform choices. These decisions are made at the start of the project. However, this month’s topic covers the other end of the timescale, after equipment becomes old and possibly obsolete. Maintenance is not just about the measurement equipment. All test system components age and at different rates. How does maintenance affect platform choices and system design and what can you do to minimize the effects of aging?

Things Wear Out

Maintenance is traditionally concerned with assuring equipment remains operational. Calibration, lubrication, and replacing worn items were handled on a periodic basis based on how fast the component changes from its baseline.

Perhaps the most critical aspect of these traditional maintenance tasks is planning for downtime of the test system. One of the best ways to minimize downtime is to have spares. For example, have a spare:

1. DMM (already calibrated!) to swap when the test system DMM needs to be sent to an outside calibration lab.
2. Connection harness in case the pins wear out. And use intermediate wear cables to lessen wear on the main harness connections at the test system side.
3. Mechanical replacement when the ATE fixture receiver or mount wears.

Of course, some test systems have costly components (such as an Instron hydraulic tester) that need periodic maintenance overhaul and you won’t be able to afford a spare. But, the goal is still to get the test system operational as quickly as possible, so plan and assure that everything needed for an overhaul is available when you begin.

Beyond Normal Wear and Tear

Last month, in the discussion of platform choices, the length of time that the test system would be used affects the choice of system components. The stability of the component vendor, the use of standards, the PC, and OS all affected the selection of components during the system design. These decisions affect the availability of components after the system is built.

But, even with the best of planning, sometimes the test system is used longer than expected or your system design choices are out of favor faster than you anticipated. You may eventually need replacement components that are no longer manufactured. The fun starts when:

1. The measurement equipment is no longer available from the vendor.
2. You can’t find the documentation describing how to build that custom component any more.
3. You can find the documentation but the parts are no longer available.

Now what?

Obsolete Instruments

Many older instruments, such as an old HP spectrum analyzer, can still be calibrated by calibration companies, of which there are many, rather than the original vendor. So, as long as the equipment is working, it can likely still be calibrated and utilized.

If the instrument is nonfunctional, or you are concerned that it might not be functional in the near future, the four successful methods I’ve seen are:

1. Purchase a refurbished unit. There are several companies that provide refurbished equipment, such as ValueTronics, Test Equipment Depot, Metric Test, and others. To find them, do a web search for something like “refurbished HP spectrum analyzer”. These companies will typically rent equipment too, in case you decide to get a new unit and need to buy some time.
2. Purchase an unwanted unit. Check auction sites, such as eBay, for someone selling their old equipment. Some of these are refurbished units and are another outlet similar to the previous bulleted option.
3. Simulate the unit with a PC and new instrumentation. We’ve had good success with this approach for GPIB equipment. The PC receives GPIB commands from the test system computer as intended for the old instrument, parses the command to execute it using the new instrumentation, and responds with the results over GPIB in the format that the test computer would expect. Except for possible timing issues (the new equipment is likely faster than the old), the test computer doesn’t know any equipment was replaced.
4. Purchase a new unit and rework the application software to support it.

Lost Documentation

This situation is classic reverse engineering. Get out your DMM, scope, and tape measures. It’s time to figure out all the components and connections. Mechanical components can be tricky to reproduce due to unknown tolerances. Electrical components at the PCB circuit level can be especially tricky. Talk with us if you have this issue. We are experienced in reverse engineering and our custom instrumentation capabilities might be of use for circuit boards.

Documented but Obsolete Components

This situation has elements of the obsolete instrument and lost documentation because it’s likely that that obsolete component will not have its specifications listed anywhere. In this situation, you have some idea about what to build, but need to find equivalent replacement parts and you don’t know what “equivalent” means.

Accessible

Finally, parts and components that need calibration and other periodic maintenance should be easily accessible. For example, such components should be put near the exterior of the test system unencumbered by harnesses, mounting plates, power distribution, and so on. Obviously, it’s a bad idea to bolt a PXI chassis right behind a 19” rack patch panel or ATE terminal blocks without an easy way to access the modular instruments inside the chassis for calibration.

Conclusion

Test systems seem to have a way of being used for longer than expected. We see this happen frequently and especially for medical devices and military components. Proper periodic maintenance will prolong test system usage. Design your test system for easy access to the components needing maintenance. Finally, when components become unavailable, I described some methods to keep the test system alive.