How to Calibrate a Weighing Scale
Weighing scales are a whole lot more important to business than you might think. Grocery stores use them to calculate the cost of fruits and vegetables. Shipping departments use them to calculate shipping and handling costs. Laboratories use them to weigh raw materials. Pharmacists use them to ration out medicine.
One of the most popular scales — the kind most e-commerce websites use to save time at the post office — is a postal scale. If the postal scale is calibrated wrong, you can bet your package will have some issues with delivery.
Calibration of a weighing scale is key to getting an accurate reading. Whether you’re working with a digital or analog scale, you still need to follow a proper scale calibration procedure to get an accurate weight.
Scale calibration procedures are extremely important because weighing instruments are used in a number of legal fields. Sure, if your produce scale is off, you might miss out on a few cents, but if the weight of, say, a 15-wheeler is off, that could pose some major safety risks. If you give someone the wrong volume of medicine, that could also have disastrous side effects.
The calibration of weighing scales is typically rated within a specific quality system. Most often, for healthcare, air and marine traffic, safety and forensics, this is the ISO 9000 system. This system is mandated by law.
Digital scales aren’t really the most accurate type of scales out there, so calibration is extremely important. Some digital scales calibrate automatically when they are turned on and the sensors don’t detect any weight, while others require you to opt into a specific calibration mode.
To calibrate a digital scale, set it on a flat surface and choose a weight. Turn the scale on and go into calibration mode. Put the weight on the scale and wait for it to calculate the total weight. If the weight is off, hit the calibration button and wait for it to recalibrate. Make adjustments if needed. Once you take the weight off, it should show zeros or “end” on the display.
Unfortunately, calibrating an analog scale is difficult – and you probably need to get it serviced by a professional because something is off balance within the hardware. You can, however, test to see if the scale needs to be calibrated in the first place.
Place the scale on a flat surface (it’ll be inaccurate on a rug or mat) and place a weight on the scale. You can use dumbbells, a gallon of water (which is eight pounds) or really anything you know the exact weight of, but standard weights are best.
Next, put your items on the scale and record its weight. Do this about three times just to check and see if it’s always the same number. The number should reflect only a small margin of error. If it’s outside of that margin, you need to get your scale serviced professionally.
The balance calibration acceptance criteria — or margin of error — of your weighing scale should be within a certain threshold depending on the type of scale you use. If you’re self-calibrating a digital scale, the display should read something along the lines of 0.000 after self-calibration. Test the scale using standard weights at 0.02 grams, 0.05 grams, 0.2 grams, 1.0 gram, 10 grams and 20 grams. They should read no different than +/- 0.1 percent of the value of the weight.
Balance calibration acceptance criteria changes if you’re doing an eccentricity calibration, which measures the weight of something in different positions on the scale’s pan. Test it with standard weights of 0.01 grams, 0.1 grams, 5 grams and 50 grams, but the reading should not exceed 0.06%.