Q: What do you love about being a biomed?
A: The opportunity to continually learn, the anticipation of what this day may bring and the ability to practice and perfect my problem solving talents The smiling faces and thank yous don’t hurt either.
A: Good question. I have been asking this to myself lately a lot. Why did I get into this field? I went into this field because it sounded interesting when I looked at the Owens Community College career choices. At that point in my life I had changed majors several times, as I was undecided on what to do. When I was young I would build go-carts with old lawn mower engines and do electrical repairs around the house. I always enjoyed building models and flying Cox airplanes. Once I started to drive, I learned that cars needed a lot of maintenance back in the ‘70s. I changed many brake pads, water pumps, alternators, batteries and even replaced an engine, taking it completely out of my 1977 Cutlass. I still do my brakes, change my oil, replace electrical window mechanisms and perform minor engine repairs. I found out that many in this field are handy men or women around the house. This field has provided for my family for over 30 years, with many opportunities for growth if you wanted it. Most in this field have the opportunity to be your own boss, as performing PMs and repairs in most cases, you need little to no supervision. Mastering the art of prioritizing all the service calls is a daily task for anyone in this field, so each of us becomes self employed in a way. I have found that just about everyone in this field are just good people. I remind those who I have worked with, how important our job is in maintaining the medical equipment and keeping up with regulatory compliance. In the 30 years I have been in this field, there has been a lot of change. The amount of equipment in a hospital has at least quadrupled. Technical training is very important to keep up with all the technology that comes into our hospitals. Everything is at a much faster and busier pace these days for all of us in the medical field. We might not always be recognized like we want to, but we have to remember that the equipment our field supports helps caregivers perform diagnostic procedures, monitoring, and surgeries, which often prolong and save the lives of those we serve. Do I like my job? Yes. Do I recommend it to others? Yes. Do I get frustrated sometimes? Yes. Do I feel overwhelmed? Yes. Am I proud of the work we do? Yes.
A: I always remind myself that we are responsible for the reliability and risk of medical devices that either diagnose or treat patients and all of us will have loved ones go through this. If we look at each patient we remember how important biomedical work is. I also love the high-tech, constantly changing health care environment. It stays interesting. Fixing problems is very gratifying. Figuring out how to assess and make things better is what biomeds do and what energizes me.
Q: I am having problems with excessive chassis leakage current on one of our hospital’s treadmills. It is a True Fitness model 700 [TTZ700LC] from 2007 (with a brushed DC motor). During its PM last month, the leakage current maxed out my safety analyzer (> 1999uA). I have gone under the hood and blown out all the dust from inside/outside the motor and around/under the brushes. This did not appear to help any. The brushes appear to be OK. I called True Fitness and they said this is not a medical grade treadmill but rather just a commercial one. They had no recommendations about what to do and do not even have a specification of maximum leakage current for the treadmill and, if nothing else, recommended plugging it in to an isolation transformer. So I called the motor manufacturer, McMillan, and they said their specifications of upper leakage current is 2000uA – but I don’t know if that is where the problem is.
So the long and short of it is, I am not sure where all the leakage current is coming from or how to reduce it. Perhaps there is an issue with the transformer on the motor control board. Any advice would be appreciated. The treadmill works OK otherwise, and the ground resistance is OK. Last year, the chassis leakage current was 20.6 uA.
A: Is the leakage there at idle or only when the treadmill is running? If it is there at idle I would unplug the motor and see if there is a significant drop in leakage. With the motor unplugged check resistance from each brush holder to the chassis of the motor. With brushed motors the leakage is often caused by excessive carbon dust buildup. Unfortunately, at that point, just blowing them out may not be enough because the dust clings to the outside of the brush holder causing a current path from the brush to the chassis.
A: One time, years ago, on a Friday afternoon, here at my hospital, I was told to check in four new treadmills for our brand-new cardiac rehab area. Each treadmill came in at 1.2 mA, or 1,200 microamps. I refused to allow their use. Several people got annoyed. But my director backed me up. After some research the next Monday, and no they were not being used, we finally found that in order to stay in code and to safely run these treadmills, each one had to have a second, independent ground wire run from the chassis to a permanent ground. The electricians were not happy with me either, but they got it done that Monday and the treadmills passed and were operational. The company was notified and they came out a week later and changed the power supplies in all four of them. I retested them and they were within our limits. So I’d suggest running a second ground wire.
A: I’d go with the isolation transformer except if your past reading is correct, a problem would be indicated. My guess is the old reading was wrong. Disconnect the motor and take another reading.
A: Could be the motor – carbon tracked from the brush dust. In the really old days we would take it out and take it apart and flush it out with blue shower or you could take it to a motor shop and have them do it. Or you can put a fixed redundant ground on the mill. Leakage current always takes the path of least resistance, so when you do your leakage test it should come out at zero.
A: I had read about possibly running a second dedicated ground wire (or an isolation transformer). Turns out, the brush clips were not seating properly, even after many attempts and experimenting. Once they were seated properly, the leakage current was acceptable.
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