Selecting Calibration Weights for Digital Scales
Calibration weights for digital scales are key elements to ensure, in the simplest sense, that you get what you pay for. For many of us this is exemplified by visits to the deli counter in the supermarket. We want assurance that the weight shown on the scale is accurate. The U.S. Government’s Weights and Measures Division sets the guidelines. Here we describe the role of calibration weights for digital scales in keeping scales accurate.
But first….
Why Digital Scale Calibration is Important
Granted, we all want assurances that the weight displayed by a scale is accurate.
But it does not take much to throw off the accuracy of a digital scale. We cover this in our post on weighing accuracy. While that post focuses on analytical balances, the importance of calibrating digital scales is no less important.
It is absolutely essential that all steps needed are taken to ensure precision digital scales consistently deliver accurate readouts (the smallest weight difference that can be displayed for a particular model).
For example, the Kern PCB 2500-2 digital platform scale with a maximum capacity of 2500 g has a readability of 0.01 g. The industrial digital platform scale DS 10KO.1S has a maximum capacity of 10 kg and a 0.1 g readout.
While certain analytical balances referenced in the above link offer internal calibration, digital scales require the use of external calibration weights to check their accuracy. These weights are purchased separately.
External calibration of digital scales, by the way, is not that complex. Operators do not have to perform adjustments during the exercise.
Procedures are spelled out in operation manuals and usually consist of selecting the “calibration” mode, placing the correct calibration test weight (more below) on the weighing plate and activating the procedure. The digital scale will adjust itself.
Selecting Calibration Weights for Digital Scales
When using an externally calibrated digital scale the calibration weight should be as close as possible to the maximum weight capacity of the scale. Recommended test weights are provided in user manuals.
But there is more.
Once the test weight is specified, the weight itself can be selected based on 7 International Organization of Legal Metrology (OIML) accuracy classes ranging from E1 to M3, where E1 is the most accurate and M3 the least.
OIML recommendation R111-2004 covers multiple weight ranges from 1 mg to 5,000 kg showing maximum permissible errors (MPE) in terms of ± mg. This increases to ± g as sample weights increase and accuracy decreases.
As an illustration the E2 80 g MPE for a 100 g test weight is ± 0.16 mg. The E1 MPE for this test weight is 0.05 mg; the M3 MPE is ± 50 mg.
Calibration weights for digital scales are also manufactured to precise standards and must be handled carefully. Importantly, these test weights must also be recalibrated every six months if used intensively; otherwise annually.
Please call the Tovatech scientists for help in making your decision and as a source for calibration weights for digital scales with internationally valid traceable calibration certificates from Kern’s accredited calibration laboratory.
