I used to work at Nordson Corp., and it was there that I ran into two Sherlock-worthy problems:
First, the company had hot-melt glue applicators ranging from units with small tanks (that glue was added to as small pellets or chips), up to a 55-gallon drum in heated-platen units. One of the 55-gallon drum units had an overheating problem.
When the line started, the LED indicators flashed, showing the heating cycle. The temperature display showed the temperature was rising. As the temperature neared the set point, the PID (proportional integral derivative) compensation was supposed to reduce the heat, and the LED flash rate slowed to mimic the change. But the temperature kept increasing until the over-heat tripped.
When this happened, the unit had to be allowed to cool before any testing could be done. The heating was controlled by a triac (triode for alternating current). When the unit cooled, I monitored the triac control voltage and output voltage. Even when the triac control was not on, it was heating, so the triac was shorted.
When I explained to the manager that I would need to replace the triac, he said that there wasnít a replacement in stock. I checked stock myself, and found a replacement that would work. The triac for the 55-gallon unit was the same triac as was used on the tank-style unit. The two had different Nordson part numbers, but they were the same triac. After I replaced the triac, the over-heat problem was fixed.
Next, I experienced another line snafu. Our company had sealant dispensing units at the General Motors Oshawa Car Plant. There were two units on one line, and one wasnít working properly. The plant was still in start-up, so the problem was not urgent. Another technician had been working on the unit, but had not been able to fix the problem. I was asked to look into the situation. I asked the technician for the details of all the testing he had done.
He narrowed the problem to a ribbon cable, but when he replaced the cable, it didnít fix the problem. When I got to the plant, I asked if it would be a problem to shut down the other, working unit. We shut the working unit down, pulled the ribbon cable, and installed it on the non-working unit. That unit powered-up and worked. We then installed the suspect cable in the first unit. That proved the cable was the problem. The replacement cable also happened to be faulty. When available, swap-tronics can be a big help.
This entry was submitted by Glenn Aitchison and edited by Rob Spiegel.
Glenn Aitchisonís first field service job was in 1987. Since then he has worked in robotics, automotive, as well as industrial automation and machinery. He received his Certificates of Qualification as an Industrial Electrician and as an Industrial Mechanic (Millwright).
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.