I worked in a biomedical equipment service department for a large university hospital, where a new building had just been finished, and all nursing units were moved in. Shortly after the move, our central sterile processing department started sending us IV pumps that were returned from new nursing units because of discharged backup batteries. The batteries are normally only used during patient transports or power outages. The standard nursing practice was to keep devices with rechargeable batteries plugged in while in use or in storage.
At first it was just a couple pumps a week from one model of a manufacturer’s pump. All of the returned pumps did indeed have depleted batteries. When we tested the charge/discharge characteristics of the sealed lead-acid batteries in the returned pumps, they indicated normal operation of the charging circuits and normal battery run times. The pump manufacturer did not have any suggestions beyond what we had tried.
As a precaution, we replaced the batteries and the pumps and returned them to service. We kept an eye out for these particular pumps, but other pumps with discharged batteries started showing up, and were not coming from the same serial numbers. Pretty soon, a variety of IV and syringe pumps from different manufacturers started coming in with the same problem. We compared our service records with central sterile processing’s equipment assignment records. Those records indicated almost all problem pumps were returned from the new neonatal Intensive Care Unit.
Since this was a new building, we now suspected that there might be outlets that were intermittent or not powered. Again, we coordinated problem pumps with bed assignment histories. We checked all the outlets but found no anomalies. We even installed a power line monitor on suspected locations, but to no avail. Nothing connected the dots. We asked the nursing staff to immediately report any questionable pump battery failures to us, so we could do an onsite investigation.
With a report of another pump battery failure, I had a facilities electrician accompany me to the patient room. The pump was indeed in “low battery” mode, even though it was plugged into an outlet. While standing around rehashing possible failure scenarios, the electrician noticed that the plug of the offending pump was plugged into the power outlet at a slight upward angle. I reached up about six feet and reseated the plug, with some difficulty, into the outlet. The pump immediately went into the “battery charging” mode.
The problem? The hospital had new “hospital-grade” outlets with very strong contact retention-force that required more than normal pressure to insert the power plugs. If the plugs were not inserted far enough, any movement of the cord could eventually cause loss of contact and force the pumps into an unintended “battery mode.”
This entry was submitted by Ken Moffett and edited by Rob Spiegel.
Ken Moffett holds a BS in industrial arts education from Iowa State University. He is currently employed as a scientific instrumentation technician for the science division at Macalester College in St Paul, Minn.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
I give an A++ to the guy who suggested lighted plug. What a great idea and simple solution to the problem. No light, no juice. It's the simple things in life...
Isn't there a saying about the impossibility to make something idiot proof because there will always be a bigger idiot. At the same time we as engineers need to be trying to do all we can to make everything work as much as possible.
Quite often in a case like this it's people working hard and doing the best they can that struggle with something that should be easy to do. But under the wrong set of circumstances it doesn't perform the way it is expected.
You would think they would have a little light on there just like on the battery powered drills that says "charging". Seems like a simple problem to be solved.
Yes, a feedback loop would have done wonders to correct the design. Given the wider acceptance of collaborative tools, it looks like feedback loops -- that could have helped here -- are beginning to sprout. It will be interesting to see if news from the field begins to alter design.
The lighted plugs do have their advantages. The light works as a quick troubleshooting tool that comes in handy especially at the end of a long extension cord.
Again, the concept of switching to a nonstandard plug/socket on medical equipment is precluded by the fact that almost all medical devices must be able to be used in almost any environment...for convenience, economic, and safety reasons.
The high placement of outlest iwas the real issue, and in most patient stations these are only used for permenently installed monitors. The new NICU was/is a highly device intensive environment...maybe more than they planned for. Research hospitals are always pushing the edge of technology for patient care...which can mean more equipment.
One change that I see now that could have made a small difference is the orientation of the outlets. In the past the outlets were installed so that the ground pin was on the botom. At that time the concern was to maintain the contact with the ground if the plug was partially pulled by tilting. This was for preventing electrical microshock to patients. Now the outlets are installed with the ground pin on the top. The power pins are the last to lose contact if the plug is tilted downward.
I like the lights in the plugs. I see them in "cheap" extension cords at Home Depot. It sometimes amazes me how nickle-and-dimey manufacturers can become on $50K-100K devices.
Good job on the go and see approach to solving the problem. In a previous job, we had a similar problem with power supplies on bench weigh scales that would suddenly stop functioning. The warranty held on the first few units, but after three failures, the scale company said that we had a problem as their units typically do not fail. Review of the systm showed that some of the plugs were to be used only for industrial fans and these had a hard wired power monitoring / controlling circuit designed to minimize power usage while using the fan. When a scale was plugged into this plug, the monitor would effectively drain the power supply and cause it to fail. We changed the plugs for the fans to a round 120 V plug which eliminated the possibility of plugging the scale into that plug.
I have come across these types of "improvement parts" and similar problems. From time to time the developers will provide a notice to the end-user as a warning so such events don't happen. Sometimes the smallest change or improvement can cause big problems.
This case includes two examples of the "it seemed like a good idea at the time" syndrome. The first being to put the outlets at a non-ergonomic height. Above head height is certainly a very poor choice for anything except plug in permanent lighting fixtures. The second poor choice was selecting receptacles without specifying the insertion force. Different levels are available from some suppliers.
Of course, having an "AC present" indicator on all of the battery backedup devices would have immediately indicated the problem, and it should always be provided.
The mention of twist-locking connectors is certainly a good comment, and it is applicable in a wide realm of applications. OF course, in some areas the equipment would need to have loss of power alarms to instantly allert the users to the problem.
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