The Problem: “Supplier has an intermittent fault with Holter Monitors.”
Intermittent shut down of several Holter monitors from a batch of 200 devices in use. The supplier asked us to find and solve the problem.
One of the faulty devices was sent to our Sydney workshop for investigation. It was tested and found to be working as specified by the manufacturer.
The device was tested under mechanical stress, varying temperature and humidity with no fault found or any interruption to recording over several days.
The device was returned for field use, however, within 1 week, reports of the problem re-occurring on several devices were received.
After hours in physical use, with the regular motion of the device, it appeared to have an unreliable connection.
Recordings would be intermittently interrupted, sometimes for hours. Totally unacceptable as critical events would be completely lost.
We requested the supplier send 4 Holter recorders complete with patient leads and batteries for further investigation.
Once again the Holter’s were bench tested with batteries and leads supplied by the supplier and no fault detected.
One Holter monitor was then fitted to a test patient for 24 hours and then it was found that the unit did in fact shut down on the first evening of use.
After testing the voltage and capacity of the batteries it was found that they still held over 70% of their capacity. It was found that if the device was aggressively jolted, the power would
- Motion was the main cause of failure.
- Due to the limited space in the battery compartment, it was found that the battery holders were fixed, not-typical of battery connectors and they had no room to stretch, therefore no pressure was applied from the connectors to the battery.
With a snug fit, this would normally not be a problem as it was a common belief that all AA batteries are the same in dimensions. But that’s not the case We compared the dimensions on 12 standard AA batteries and found variations in some brands of up to 200 microns in length.
The supplier was using a shorter in-consistent brand, which appeared normal to the naked human eye, and often functioned when first installed.
However, after hours in physical use, with the regular motion of the device, the shorter battery proved to have an unreliable connection.
Recordings would be intermittently interrupted, sometimes for hours. Totally unacceptable as critical events would be completely unrecorded.
The Good News
We advised the supplier to use a battery that was manufactured to a more consistent quality of dimensions.