Verification of patient scale accuracy

Are you working on a specific scale? Make/model? 

No, this is more a general question about how other biomeds / hospitals handle the question of patient scale accuracy verification.

Since a scale is a strictly linear device, you don't need a huge set of calibrated weights. We have a weight that was certified at 17.8 pounds, and it is used to verify all of our scales.

First, the scale is zeroed, which is one point in determining linearity.

Then, the 17.8 pound weight is placed on the scale. If it shows as 17.8 pounds ± 2% we have the second point in determining linearity.

Finally, A third unknown weight is weighed. If the patient scale is an adult scale, I weigh myself. This weight doesn't matter, because the next step is to weigh the same weight again PLUS the 17.8 pound weight. If this final weight is the item's weight plus 17.8 pounds ± 2%, then we have established linearity along three points, which is all that is required.

In that third step, you do not have to know what the item (in my case, myself) actually weighs, all you are doing is ensuring that the scale you are testing is weighing that additional calibrated weight the same whether it is added from 0 or if it is added at 80% or 90% of the scale's capacity.

The ± 2% seems to be a normal standard for patient scales; most are well under 1%.

Thanks Dean; this is exactly what I needed.

You're welcome!

Glad I could help!