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.
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 … Read the rest
University and industrial laboratory researchers requiring extremely accurate measurements of extremely small quantities rely on a precision instrument called an analytical balance. Shopping for an analytical balance requires being familiar with some of the advanced features available today as well as the proper use of these precision instruments. It is on the second point that we focus this post on how to use an analytical balance.
Here you will learn
- How to set up an analytical balance
- The effect of environment on weighing accuracy
- How samples can introduce errors
- The importance of personal practices
- Important maintenance tips
Weighing accuracy is a primary criterion for precision scales, analytical balances and moisture analyzers where readout (the smallest weight difference displayed) and linearity (the ± deviation from the actual weight) are governed by GLP, ISO and other standards. Test weights have a critical role to play when scales with capacities from milligrams to tons are not automatically internally (see below) calibrated . The type of calibration, whether internal or external, is indicated on scales’ spec sheets.… Read the rest
Accuracy and precision (there is a difference) in the performance of analytical balances are crucial when weighing extremely small masses such as to 0.1 or 0.01 mg. Even the smallest deviation in accuracy can throw off critical measurements when compounding, for example, pharmaceuticals and weighing active pharmaceutical ingredients (API). For this reason analytical balance recalibration exercises and procedures should be carefully spelled out in a company’s standard operating procedures.
The Effect of Gravity on an Analytical Balance
Manufacturers of analytical balances such as the Kern line available from Tovatech call attention to the importance of calibration and recalibration early in their instruction manuals. Kern points out, for example, that gravitational pull varies throughout the world due to the fact that the world is not a perfect sphere. This was demonstrated a few years ago by shipping the Kern Gnome to many locations around the world. The Kern Gnome was accompanied … Read the rest
Strong emphasis is placed on the importance of calibrating analytical balances in laboratories, universities and other areas where accurate and precise weighing to 0.1 or 0.01 mg is required. Even though a balance has been calibrated by the manufacturer it must be recalibrated locally.
Why is this so crucial? The results displayed on the balance are impacted by gravity. If Earth were a perfect sphere of uniform density, then gravity would be consistent. But it’s not, which means gravity varies wherever you go. While a person’s weight may not noticeably vary whether in Japan, Germany, Australia or North America, when weighing in milligrams gravity does impact results. And that explains the title of this post.
A Calibration Point Proved by the Kern Gnome
Kern & Sohn, manufacturers of analytical balances and digital scales offered by Tovatech, conducted an interesting experiment a few years ago by shipping a little fellow called … Read the rest
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
The primary measure of the effectiveness of a pharmaceutical product is how beneficial it is for the patient, while introducing minimal side effects. A vital part of the pharmaceutical manufacturing process occurs at the quality control stage. A variation of a few milligrams in a powerful drug can mean the difference between a nightmare of side effects, a harmless and ineffective placebo, or a valuable treatment method. The key to ensuring that a “wonder drug” achieves the goals that the developers set out for it is careful measurement via a laboratory scale.
Types of Laboratory Scales
Just as various types of microscopes offer the ability for researchers to see items ranging from bacteria down to molecules, different types of laboratory scales offer the ability to measure items to within very small masses. These scales carry specific names to differentiate their levels of readability:
- Precision balances vary in resolution and some have
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
Last week we showed you a brief video on how to use an analytical balance. This is a much more detailed video explained by Professor Yee of thinkwell.com. This demo explains different aspects of the Analytical Balance in clear, umabiguous language that is easily understood.… Read the rest
Determining the density of a solid or liquid is easier and more accurate when using a density determination kit with an analytical balance. Analytical balances such as the Kern ABS, AES and ABT models available from Tovatech can be programmed to work in concert with density determination sets, showing the density directly on the analytical balance liquid crystal display.
These density determination kits work on the buoyancy method, based on Archimedes’ Principle and recognized for a high degree of accuracy. As an example, 10 cm3 glass plummet is used for measuring the density liquids, giving a resolution of 0.0001 g/cm3. The density is determined from the weight of the plummet in air and its weight in the liquid being measured.
For solids, the density is the ratio of the object’s weight in air and its volume. Volume is determined by the buoyancy of the sample when immersed … Read the rest