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Technical Support Nightmare
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Some Potentiostat installations can be particularly vexing. Here's one story.
A customer called our technical support and explained that he had tried to perform a long-term (many day) potentiostatic experiment. The experiment would run for many hours. Too often, however, he would arrive the next morning to find that his computer had rebooted and was waiting at the
Windows® Login screen. We were suspicious of a software problem. However, many customers had run long-term experiments using the same software without problems We suspected that the computer did not have enough memory. He increased the memory to 512 Mbytes, but the problem persisted. We postulated that there was some strange interaction with another subsystem installed in his computer. He sent the entire system, computer and all, to us. It ran continuously for over a week at our office without problems! We briefly considered that his laboratory might be haunted! Meanwhile, another of his Gamry Potentiostats started to give erroneous readings. It was returned to the factory for in-warranty repairs and we found that the inputs to the electrometer had been "blown." We repaired it, and returned the unit to him -- with the admonition to be mindful of static charge and not shuffle his feet in the lab! A few weeks later, he reported the same problems with another Potentiostat, which was also returned for repair. This one, also, had sustained damage to the electrometer inputs. Could this repeated damage and the computer problems be related? “What, exactly, are you doing?” we asked. When he told us, we remarked that, although his experimental setup was unusual, it was not outlandish. He was studying the long-term corrosion of a steel sample. To keep any corrosion products from building up, he had constructed a flow loop to slowly replenish the electrolyte. The counter electrode was isolated by a sintered glass frit to keep the counter electrode reaction products from contaminating the electrolyte. The electrochemical cell was all glass and all of the plumbing was made of good quality plastic. A peristaltic pump kept an overhead reservoir filled. The electrochemical cell was gravity-fed from this reservoir. After passing through the cell, the waste electrolyte was collected in a plastic container. Except for his working electrode, no metal came in contact with the electrolyte. This eliminated possibilities of metallic contamination. It also electrically isolated his entire system. We formed the following hypothesis. Suppose the action of the peristaltic pump was slowly generating a static charge. The static charge might build up on plastic plumbing. Eventually, the voltage would become high enough that it would discharge through whatever was handy. Sometimes that might be the input to the differential electrometer, overcoming the protection circuitry and damaging the input buffers. Other times it might be associated with the computer, causing the computer to reboot. Although this sounded preposterous, we remembered Sherlock Holmes’ words in “The Beryl Coronet”: "It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth." If we could discharge the static electricity before it zapped the electrometer or the computer, the problem would be solved. We suggested to our user that he place a piece of platinum wire in the waste electrolyte container and connect it to earth ground. The static charge could bleed off harmlessly through the electrolyte to the platinum. Because the platinum was in the waste container, the flowing electrolyte would remain uncontaminated. Because every Gamry potentiostat is isolated from earth (or “floating”), the platinum would not disrupt any of his experiments. Although it sounded like black magic, our user tried it. Guess what! He has not been plagued by zapped electrometers or by mysteriously rebooting computers since the platinum was added! His week-long experiments ran to completion! Tech Support is getting lonely. Our user never calls, except to place an order! Isn’t science wonderful! |
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Gamry
Instruments © 1997-2004 |
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