Instrumentation Troubleshooting Part 3 By Mark Williamson
Proper power and grounding are essential for all electronics needless to say but sometimes overlooked by even some of the most experienced technicians. Just because you can read a voltage and the voltage seems good does not necessarily mean that the power is adequate.
So you have made a ground with one lead from your VOM and using the other to check voltages at various points and all seems good. Did you check all the grounding points? If your supplied power at the source is much higher than the power connection to the device, there could be a problem with corrosion at one of the connections from the power source. Lengthy runs of cable will cause a voltage drop as well as undersized wiring.
I’ve seen melted fuse holders due to bad connections in the fuse holder. In glass fuses it is easy to see sometimes that the fuse was burned off at one end indicating that there could have been a bad connection in the fuse holder. Resistance causes heat and a loose connection can cause heat.
Proper fusing is important to protect the wiring as well as the device.
I was called to go to a location where an operator had lost serial communication with his equipment but the operators panel on the equipment was still working. Before I got to the location he called me and said the operators panel wouldn’t display either. When I got there, a quick voltage check showed about 9.5 vdc. I went to check the alternator and the belt was missing. Jumper cables to the battery, they were able to continue pumping and then serviced the equipment when the pumping operation was complete.
Another time something similar, and I ask him to check his alternator. He couldn’t find it. It was there but hanging off the side of the equipment. The bolts had come loose. Simple things but critical to the operation.
Some techs get tagged with the name of Black Box Changer and maybe for some of them, that is really all they know how to do and it can get you into trouble depending on the situation. We are not all fortunate enough to have identical equipment to use as ready spares and even though parts appear the same they may have different voltage requirements or output different signals.
Some vendors may have several models that look the same but perform different functions with the addition or deletion of chips or jumper settings on the same basic board layout. It can be in just how it was programmed.
Many newer designs offer a wider latitude in required voltages making for easier integration into existing systems and may have functions that are not relative to your application.
A couple of industrial computers and transmitters commonly used in the oilfield have a problem if they are left on while the battery discharges slowly. This will cause them to lose their settings in memory. I’ve seen this happen with some MD/Totco and Thermo Fisher equipment and I’m sure there are a lot more of them out there in legacy equipment. Don’t you just love it when you read the message “This Unit Has Not Been Setup” or the units of measure are all something strange.
Bad grounds are often overlooked and can the culprit of many problems.
A lot of systems are 24 volts, while others being 12 volts. I have seen times where 12-volt equipment was added to a 24-volt system by making a connection to the common point of two 12-volt batteries tied in series. This leads to one battery being over charged. Although it works, battery replacement is much more frequent and ends up costing much more than it would have cost to do it right in the first place.
Swapping parts in troubleshooting sometimes can work but be warned, what caused the part to go bad may cause the swapped part to go bad as well and if it came from a working unit now you end up with two nonworking units.
We were performing toxic fueling operations and in this process we had a scrubber to evacuate any spilled fuels and neutralize them. It was the hottest day on record when the scrubber tripped out on a thermal overload. The backup scrubber kicked on and shortly afterwards tripped out on a thermal overload. After much investigation and many meetings, we convinced them that the cause was due to the ambient temperature and not an equipment malfunction. The overloads were upgraded by 20% and I doubt they will ever see that problem again.
On a chill water HVAC system when alarms were sensed it was supposed to exhaust the room to the roof. This had never been properly tested and when it was tested the chillers shut down. We had several chillers and this one was the only one with a problem. When it went to exhaust mode, it short looped the chill water and shutdown for freeze protection. Costly but was remedied by adding a volume tank in the chill water system.
Sometimes it is just a design problem. Don’t get fooled by someone wanting you to fix something that never worked to begin with.
We had a fire suppression sprinkler system that had to have two at least 2 detections to trigger the piping being charged and the final would be to melt the element in the sprinkler heads. With a spacecraft in the bay, the alarm went off and pipes charged. When the building was constructed the piping had been hydro-tested. Not all the water had been removed. Corrosion had caused a hole in the piping, dropping the air pressure and an infrared sensor had malfunctioned.
Sometimes things are just lying in wait to spring up at the most inopportune moment.
On a small pressure pumping operation, they were having tub level problems with their blender. When I got there, they were swapping out blenders for the third time. While waiting for another blender, the pump operator asks me if I could take a look at one of the pumps. It kept kicking out of gear. They were only running four 1800 horsepower pumps. With loosing 25% of their flow rate and suddenly getting it back, you don’t have to wonder why they were having some many problems with the tub level being inconsistent. I ask him why he hadn’t reported it to the supervisor. “Well, they were having so much hell with the blender, I didn’t want to bother them.”
Proper orientation of cord grips, clean and tight connections, drip loops, tight covers, weather seals, O-rings, gaskets, tight connections, tight back shells, good solder connections, proper sealant and frequent inspections all contribute to a successful operation.
I had a boss once upon a time that was trying to come up with a job description for what I did and he called me into his office. He said he had finally figured out my job description. “Fixes everything that is broken and if it’s no broken, figure out how to make it better. I think that just about covers it.”
Having a working knowledge of the system and good drawings or schematics is important but they are not always there.
A couple of things to remember that you should already know, water and electricity don’t mix and if you are probing around in something unfamiliar keep one hand in your pocket so you can’t provide a path across you heart and when you get through making a repair, inspect you work and strive to make your repair work look as though nothing had been disturbed. Keep it uniform.
Be safe and remember the sole purpose is to make a profit for the people that employ you. If they can’t make a profit, how can they continue to make the payroll.
Comments