November 6th, 2009

Inexpensive Noise Filter Helps Reduce Scale Drift Problems

PACT scaleElectronic scales, even expensive lab-grade units, can be influenced by a wide variety of electronic “emissions”. We’ve seen Chargemasters being affected by cordless telephones and older CRT computer monitors. When stray emissions interfere with digital scales, you can get erractic readings, or the scales can drift with time. The smart thing to do, of course, is to physically isolate your digital scale from the sources of interference — keep them away from computer equipment and wireless base units. If you still have problems with drift or unstable read-outs, thankfully there are some inexpensive accessories that can restore your scale’s reliability. Reader Scott G. found a ferrous (magnetic) filter that attaches to the cord of his digital scale. This inexpensive filter cured his scale’s tendency to drift.

Scott explains: “I had an issue with a drifting zero on my PACT, which made it unusable. It was happening at my house, but not at other locations, such as my office. The fix for my issue was a ferrous noise filter on the scale’s power supply cord. It is basically a hinged barrel-shaped plastic tube that contains two magnets. Near the scale end of the cord, lay the cord into the slot, wrap it back through, then close the filter around the cord. Before installing the ferrous filters, my scale would drift off as much as 2.9 grains, which was being caused by some type of electronic ‘noise’ in the environment. The PACT is absolutely stable now.”

electronic noise filter

Finding and Installing Magnetic Noise Filters
Scott tells us: “You’ll see a lot of these type filters on the cords for computer acessories. You may have to experiment to find one that works for you. Some have different magnets that have different filtering abilities. My filter cost about $3.00. I purchased it at Randolph and Rice Industrial Electronics in Nashville, TN, item #SF.065.” You should also be able to find these kind of filters at Fry’s, Radio Shack, or other electronics supply stores.

electronic noise filter

While some magnetic filters require the power cord to run straight through, other designs allow you to loop the cord once around the filter (see photos). Looping the cord actually enhances the performance of the filter. You can also get improved filtration of electronic interference by putting a magnetic ‘noise’ filter on BOTH ends of your scale’s power cord.