Gempro 250 question

C

Carl Darnell

Guest
I have a Gempro 250 and have just started using it. As I weighed the charges I noticed that if I get the weight I want on the readout and wait about 30 seconds the reading drops. It I wait another 20-30 seconds it drops again.

Today I decided to see just how much it would drop and set the scale up and put a 50 gn bullet on the scale, took it off and put it on a few times. The readout showed about +/-49.90 gn with each reading.

Then I decided to leave the bullet on the scale to see how much it would drop. After about an hour the readout had decreased by .02 every 20 or so seconds and is now reading 47.30. I am thinking if I leave it on the scale for 24 hours it will read zero.

Has anyone discovered this or is my scale defective? It is brand new and I have only had it a few months and just started using it. I guess I have loaded about 200 rounds with it. What I have been doing is putting the powder on the scale until I reach the weight I want and watch it for about 30 seconds while it settles down and dumping it into the case.

Now I am wondering if an electronic scale is really accurate and worth using. Or, am I using it wrong.
 
I think I have solved the problem. It appears I have not left the scale turned on long enough to stabilize. After about 2 hours I rechecked the bullet weight and every time it came out at 49.88 and the scale didn't change.
 
There are two primary types of scales capable of measuring powder loads. One is a Strain gauge measurement and the other is magnetic force restoration. The latter balance is zeroed to a 0.000 level and when you them put a mass on the pan( I.E. powder charge) The pan lowers proportionally to the mass on the pan. Then, a very accurate current is forced through a solenoid which raises the pan magnetically till it reaches zero again. The current is converted to a metric like Grams or Grains.
The strain gauge type again zeros with no mass on the pan to read 0.000. Then, when a mass is placed on the pan, the resistance of the strain gauge is measured and its resistance is converted to a unit like Grams or Grains etc. The strain gauge scales also usually have an automatically self adjusting zero that will maintain a zero reading regardless of drift in the strain gauge. So, if you place a mass on the pan, the initial measurement is quite accurate. Then, if you trickle, the scale thinks it is off by that granule weight and it will begin to decrement toward zero in a programmed time. Meanwhile, it will not indicate the trickled weight but maintain the last weight prior to trickling. That is why folks trickle then push on the pan a bit and it will make a new measurement. This time including the trickle. Magnetic force restoration do not need these auto-zero features as they are more stable than a strain gauge.

It is this auto zero that makes the scale drop in weight every so often. It is auto zeroing back to zero but one small step per time interval.

If you understand the idiosyncrasies of the strain gauge, you are fine.
 
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