October 3rd, 2015

Ten Commandments for Use of Electronic Scales

Denver Instrument, maker of the MXX and Timberline Series of precision balances, has created a helpful guide explaining how to get the best performance from a digital scale. Denver Instrument knows that, to achieve and maintain a very high level of accuracy with digital scales, they must be calibrated regularly, leveled properly, and kept away from sources of interference. Unfortunately, some reloaders treat their electronic scales as if the machines were toasters — something to place on a tabletop, plug into an outlet, then “set and forget.” There’s a better way to set up your scale and keep it functioning optimally. Here are ten guidelines provided by Denver Instrument. Follow these “Ten Commandments” and you’ll benefit:

Denver Instrument MXX-123

Denver Instrument MXX-123ONE: Thou shalt choose the best resting spot. The performance of your balance depends greatly on the surrounding environment. Choose a location away from the main traffic flow of the room, especially doors. Also be aware of heating and cooling vents as these produce air movement. You can adjust the environmental settings on your balance to provide the best performance in the chosen location. Balances must be placed away from magnets as they affect the weigh cell performance.

TWO: Thou shalt avoid vibrations. Vibrations can come from large machinery in production environments and from fume hoods in laboratories. An alternative to fume hoods are Power Safety Workstations which are designed specifically for use with a balance.

THREE: Thou shalt watch temperature changes. On an analytical balance a one degree temperature change can cause a 1 digit (0.0001g) drift. Although Denver balances have temperature correction built-in, it is still important to calibrate your balance when the temperature changes significantly. Choosing to place your balance in a temperature controlled room, away from sunlight, and calibrating often helps minimize the effects of temperature.

FOUR: Thou shalt calibrate often. Upon installation and each time the balance is moved you should calibrate your balance. For example moving an analytical balance to a location that is only 13 feet higher changes the weight reading from 200.0000 g to 199.9997 g; which means the result is 0.0003 g lighter than the actual mass.

FIVE: Remember to check the level. The instrument should be leveled upon installation with all feet (two front feet for round pan units, four feet for square pan units) touching the countertop. If the level changes, the balance should be re-leveled and recalibrated. As an example, a 200g sample would weigh 0.0025 g less when tilted at an angle of 0.3°.

SIX: Honor thy weights. Keep in mind that weights are only as reliable as their quality and certification. Remember, a 1 g does not weigh precisely 1.00000 grams. Weights should be recertified annually. Denver Instrument offers recertification services on all weights 1 mg to 5 kg. Check to make sure you have selected the proper weight class for your balance. The weight tolerance should be better than balance readability. Always use tweezers or gloves when handling weights as smudges and indentations change the value of the weight. Keep weights in cases so they don’t get scratched or dusty.

Denver Instrument TimberlineSEVEN: Thou shalt always use a small container and weigh in the center of the pan. Especially when using an analytical balance, the effects of air buoyancy increase as the sample container size increases. Using a small sample container will minimize the effects. Items placed on the pan provide a downward force. Placing them directly in the center of the pan keeps corner loading errors at a minimum.

EIGHT: Thou shalt not unplug. To perform within published speci-fications, balances must have power applied for 30 minutes to 48 hours depending on the resolution of the balance. Denver balances have a standby mode which turn the display to standby but keep power cycling through the electronics.

NINE: Thou shalt not ignore static. Static is one of the most common weighing “noises”. It can cause reading to appear too high, too low or just be unstable. Denver balances include grounding methods to reduce the effects of static. However sometimes extra supplies are needed. Consider anti-static weigh dishes, anti-static brushes or low tech ways to increase the humidity of the chamber like placing damp cotton balls or glass wool in a small vial in the corner of the analytical draft shield.

TEN: Thou shalt clean often. Dirty weigh pans and powder in weighing chamber can contribute to static issues and lead to a wide variety of problems. Denver weigh pans are made from stainless steel and can be cleaned using a variety of household and laboratory chemicals. A small paint brush can be used to get power away from the edges of the draft shield for easy clean up.

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March 10th, 2012

Shot Order and Calibration When Using Electronic Scales

Here’s a tip that can help you score higher at matches and get more predictable results when weighing loads with an electronic scale. Kelly Bachand, a top prone shooter and electrical engineering major at the Univ. of Washington, tells us that all digital scales can drift. Therefore Kelly recommends re-calibrating electronic scales often. In addition — and this is key — Kelly recommends that you shoot the ammo in the exact order in which it was loaded. Arrange your loaded ammo in a box in the order of loading and shoot it first-loaded to last-loaded. (Or, if you prefer, shoot it last-loaded to first-loaded.) The important thing is to maintain the order and not mix everything up. That way, if your scale drifts, the effect of drift on charge weight will be incremental from one loaded round to the next, so point of impact change should be negligible. Conversely, if you shoot your last-loaded round right after your first-loaded round, the effect of scale drift is at its maximum, so powder charge varience is maximized. And that can produce a different point of impact (POI) on the target.

Tips on Loading with Electronic Scales
by Kelly Bachand
If you use a digital scale to measure powder charges, recalibrate the scale often. I like to do this about every 25 rounds or so. Additionally, most electronic scales rely on eddy currents for their precision. Eddy currents are easily disrupted by static electricity so keep a cloth or ground strap nearby to remove any static currents should the scale start acting up; I usually just use a fabric softener sheet that has gone through the dryer once.

Shoot Ammo in Order of Loading
I shoot my rounds in the same order or reverse order as I load them. If the charge weight varies due to scale drift during use, the difference will be gradual if I shoot in the same order as production (or reverse order). I should be able to adjust for the slight varience in charge weight without having any wildly high or low shots (see the charts below for a graphical demonstration). I usually load my ammunition just 100 rounds at a time. Give yourself plenty of time and remember that you will make your best ammunition when you are fully awake and alert.

Electronic powder scale chart

This graph demonstrates the effect a .01% (that’s 1/100th of 1 percent) difference in scale measurement would have over the course of 100 rounds assuming the desired load is somewhere between 46 and 47 grains. The final round made would have almost 1% less (or more) powder than the first, that’s almost an 0.5 grain difference from the first. If shot back to back, these rounds will invariably have different points of impact on the target.

Electronic powder scale chart

This graph demonstrates the same .01% difference in scale measurement but this time with a recalibration every 25 rounds. By recalibrating the scale every 25 rounds the furthest a weighed charge ever gets from the original is less than 0.25%. Again if the charge being weighed is between 46 and 47 grains then the 26th round made would vary from the 1st by .12 grains. Even that small difference would likely show on target.

Either way it is important to note that if the bullets are shot in the same (or reverse) order as they are made, the biggest difference from bullet to bullet in this example is less than .01 grains.

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