Digital Scale warning

[dodgestdshift]

Yesterday, I forgot to warm up my RCBS (PACT) Powder Pro digital powder scale. After loading about 50 cases, I noticed that when I placed the empty scale pan on the scale it read 1 grain. Sure enough the "zero" had wandered and all of my loads were about 1 grain light. After breaking down the 50 loads, fortunately I had only set the bullets on the belled cases and hadn't seated them, I had to trickle in the the rest of the required load.

Conclusion:

1) MOST IMPORTANT, ALWAYS ALLOW THE SCALE TO WARM UP FOR AT LEAST 20 MINUTES.
2) Watch what you are doing, frequently check the scale to make sure the "zero" hasn't wandered. This is easily accomplished by setting the empty scale pan on the scale. It should read zero.
3) This may be controversial - Always charge all your cases then check the powder levels in them in good light compared to the others. Empty cases and double charges will stand out. I don't think it is a good idea to charge a case, and immediately seat the bullet.

 

[Jet22]

Thanks Don...I just bought one with the dispenser off Ebay. It arrived Wednsday. I have not had time to try it yet, but will darn sure let it warm up when I use it!! I am setting up a progressive to load 308's and want to weigh all the charges. I have a Lyman autoscale but I like to use H335 in the 308 and the Autoscale likes stick powder. Thanks again for the advise!!

 

[Rockstar]

Next batch I run on my Dillon 650, I'll be sure and check every charge!

 

[The Bushmaster]

I have the RCBS (Pact) electronic scale and have always allowed it to warm up before I calibrate it. Of course, I warm up every thing that I start, lite off or energize. Even my wife.

 

[Oldnamvet]

Digital balances should not need to "warm up". If your battery is fresh, you only need to allow the balance to go through its internal diagnostics before starting to use it. This should be no more than a minute or so. Having used balances extensively in my profession (31 years as an analytical chemist), some of the most important things are sometimes ignored. The balance should be on a solid, level bench. Vibration from the reloading press actuation can cause problems. There should be some type of shield around the balance to prevent air currents from affecting the weight. I set a large cardboard box with one side cut off around mine. Even leaning over the balance moves enough air (not to mention hot breath) to affect the reading. Before you start, put a check weight on the balance to be sure everything is functioning properly. Watch out for static electricity. If you are experiencing a lot of static, be especially careful and consider a humidifier for the area. Finally, if you store the balance in a different environment (such as a warmer/cooler room), allow it to reach equilibrium temperature with the room in which you will use it. In this case, it is necessary for either a warm up or cool down before use.

 

[The Bushmaster]

My RCBS Electronic uses no batteries. I have the one that has a wall plug adapter and it does need to have about 10 minutes to warm up and settle. Otherwize it will go to error until it does warm up.

 

[Six-Gun]

That's wierd. I use the Dillon Terminator electronic, and even after accidentally leaving it on for a couple of hours, it didn't drift on me.

I will keep an eye on it though, as you never know with electronics - anything could happen. I load on a Dillon XL650 as well, an somethnig like this could easily cause a dangerous situation. I check my powder charges every 50 rounds, but still...if the scale is giving bunk numbers...who knows.

I know a few buddies who have RCBS scales, and they need to know about this issue.

 

[Rockstar]

Six-Gun: How, exactly, would leaving your scale on for a couple of hours relate to a discussion about not warming up electonic scales? I'm probably missing something. I use the RCBS Powder Pro scale, with no problems, so far. There are some reloaders who leave their scales turned on 24/7.

 

[Six-Gun]

My point is that I have never seen my scale slip in calibration from its zero. Even when I turned it on, but it wasn't used it because I got distracted/side-tracked (by a phone call or the Mrs. asking me to do somethnig else just as I was about to start reloading) the zero was the same many hours later.

I assume that we are exploring the idea that digital scales can migrate from their zero as they warm up, correct? I firmly believe is true - in the Air Force, we allow our measurement equipment on the aircraft I fly on to warm up for 15 minutes before we even calibrate it. However, these are much larger, more sophisticated oscilliscopes and such which eventually generate a lot of heat.

I'm not trying to imply a product comparison at all, and maybe should've phrased my reply a bit differently. All I am saying is that the zero I have have when I turn on the scale seems to stay constant in my case - from the time it's turned on to many hours later it stays constant, thus I don't seem to have the issue of drift. I'm sure someone else with the same scale as mine could easily have a drift problem. It could easily come down to something as simple as room temperature.

 

[Deavis]

Digital balances should not need to "warm up". If your battery is fresh, you only need to allow the balance to go through its internal diagnostics before starting to use it. This should be no more than a minute or so.

That is indeed true for most electronics that completely digital but that is not always true for electronics with analog components. A well designed electronic device should not drift over time but it is rare that you have a perfectly designed device used in the exact design conditions. Drift should be expected because every analog component will change its value with temperature and also with time. Every component datasheet out there will show you how the value changes with temperature and many times over its lifetime. The latter is something very few people take into account because we toss electronics so often.

The question is whether the change in value negatively affects the measurments that you are running. For instance, you can take an ADC circuit and by varying temperature and force its acurracy to drift by several significant digits. Ever try getting a good accurate conversion at 200°C? Let me tell you something, it isn't easy. Setup a simple opamp circuit with passive components and start applying heat to them. You can watch the output change as the caps and resistors change value with temperature! However, if the manufacturer has spec'd quality components with good tolerances and made a design that addresses these issues then you should not have a problem.

Even digital devices can be forced to malfunction with changes in temperature in either direction because they are still analog devices at heart. Remember, at a fundamental level that carrier mobility is highly dependent on temperature since temperature helps drives scattering events. The strain gauge in those scales is definitely affected by temperature and I believe that the warm-up period, which is recommended by a few manufacturers in their manuals, simply reflects the electronics reaching an equilibrium temperature during operation. Self-heating effects can be really rough on precision electronics because it can start a cascade of unwanted effects.

Edit: Not to take away from the excellent advice on scale positioning, bench stability, etc... All those were excellent points.

 

[The Bushmaster]

Well I'll be damned...We agree Mr Deavis.

 

[Deavis]

We have to agree, the laws of physics dictate it on this particular subject!

http://www.atceramics.com/pdf/technotes/temp_coef.pdf
http://www.atceramics.com/pdf/technotes/dielectric_aging.pdf
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/restmp.html
http://www.omega.com/literature/transactions/volume3/strain.html

Plus it helps that there isn't a mechanical tool involved in the discussion

 

[The Bushmaster]

Besides a mastery of mechanical tools, I have a basic understanding of electronics. Mostly self taught. ( I read a lot and dabble here and there) But I would NEVER assume that I knew more then you..... In anything...I might beat you out in life experieces though...(I don't spend much time on the couch except to watch educational channels... )

 

[Waitone]

Balance beam or electronic scales. Regardless of the type, check weights are your friend. Consider them safety equipment just like shooting glasses and hearing protection. They just might keep you from leaking all over the range.

 

[BluesBear]

check weights are your friend. Consider them safety equipment just like shooting glasses and hearing protection.

You got that right!

 

[RugerGuy]

Not sure if it's true or not. I heard flourescent light could affect how a digital scale read.

 

[Deavis]

Flourescent lights are very noisy electrically. I'm sure this is common knowledge but a flourescent is constantly switching on and off as the AC power is a sine wave (or close approximation). This, like any switching, event will perturb other devices on the same circuit and in some cases other circuits if the power distribution method is not robust enough to handle the switching.

This is the same exact phenomena you see with high speed microprocessors or clock circuits when they start generating excess noise on adjacent traces (think nearby circuits) or even worse, pulling down the powerplane around them during switching (turn on the vacuum and watch the lights dim in your poorly wired 16ga houses!). Current is only dissapated during a switching event for a CMOS device (a little over simplified) and the same happens on a flourescent light when the light arcs.

So, you have digital scale requires a constant 120V at its AC->DC converter to source exactly the right amount of current/voltage and you have a bank of lights firing on and off. It is easy to imagine that you will get dips in your power line that will affect your scale. That is why they build capacitance into power supplies, to help smooth out fluctuations in the power source.

Remember, the power coming from your electric company isn't really that clean. Everytime your neighbor's monster air compressor fires up, the utility turns on a large air conditioner, so forth and so on, the power line will be affected. Depending on the capacitance, it may hold or it may not. The best solution is a line conditioner for sensitive electronic devices, ie an UPS.