Posts Tagged ‘scientific digital scale’
Selecting Scale Weights for Calibration Testing
Calibrating precision digital scales, analytical balances and moisture analyzers that rely on accurate weight measurement requires periodic tests using a scale weight closely matching the maximum capacity of the instrument being tested.
Why Testing with Scale Weights is Important
Daily we depend on weighing accuracy – such as 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.
But in research labs and in food, drug and other production facilities, weighing accuracy assumes a highly critical criterion. This applies to weighing and measuring instruments where readout (the smallest weight difference displayed) and linearity (the ± deviation from the actual weight) are governed by GLP, ISO and other standards.
Adding to challenges, the accuracy of precision weighing and measuring instruments can be … Read the rest
Tips for Analytical Balance Weighing Accuracy
Accuracy is a prime if not the prime criterion for analytical balances used in industries such as researching and compounding pharmaceuticals. Analytical balance weighing accuracy is a measure of how close the displayed weight is to the actual weight of samples on the weighing pan.
Two terms apply here. The first is readout, which is the smallest difference in weight that can be read and displayed by the unit. For an analytical balance it is typically 0.1 milligram or 0.001 g. Micro and ultra microbalances can weigh lighter samples.
Accuracy is sometimes confused with precision but it is an incorrect assumption. Precise means that results are consistent. However they may be consistently wrong, and therefore not accurate.
Instead, the second term or criterion to look for is linearity. Linearity is the maximum ± deviation of the displayed sample weight vs. the actual sample weight over the weighing range of the … Read the rest
Tips on Selecting a Laboratory Balance
A lot goes into selecting a laboratory balance. Let’s start with weight. You’ll need to select a balance that displays sample weight to the resolution desired. This is described as readout. Readout can be to several decimal places presented in grams or milligrams.
Select a balance with a weighing capacity in excess of the samples you plan to weigh. Some balances also specify the minimum load that can be placed on the weighing plate.
Why is this you ask? If the sample weight is not much larger than the expected weighing error, the measured value will be neither accurate nor repeatable. For this reason the spec sheet for laboratory balances may specify a minimum load. For the Kern ABT 0.1 mg readout balances available with maximum loads of 120, 220 and 320 grams the minimum load is 10 mg. But if you want to weigh samples less than 10 mg … Read the rest