How to Reduce Measurement Errors in Pharma With Weighing by Difference

On March 1, 2022

When it comes to weighing and dispensing material in pharmaceutical industries, the precision and accuracy of the measurements are crucial as the required quantity of materials is calculated proportionally in the formulas. The scale sensibility and its calibration, among other factors, can introduce errors during the measurement.

Errors are not entirely avoidable because they are intrinsically associated with the weighing process – whether due to operator-dependent procedure or to the technological limitation of the instruments – but there is a mathematical way to reduce them during weighing.

How? With the weighing-by-difference method.

What Is Weighing by Difference?

The term “weighing by difference” refers to the fact that the target weight of the material is the difference between two weights of the container: the weight of the container before and the weight of the container after you transfer the material from the container to the vessel.

If you weigh by difference, you avoid three errors:

  1. Tare errors. Weighing with a container introduces an additional source of inaccuracy, which is the container itself. With the weighing-by-difference procedure, you eliminate the need for a container.
  2. Scale calibration errors. Exact zeroing of the scale is not essential because any error in the initial reading will be automatically canceled when subtraction of the reading occurs.
  3. Errors due to substance sticking to the container. If you weigh the substance in a container and then pour it into the vessel, a small amount will stay in the container. Therefore, the actual amount consumed in production differs from the amount you weighed. This error should be avoided, especially in pharmaceutical and biotech manufacturing, where you must consume the exact quantity you weigh.

For these reasons, weighing by difference is one of the most accurate methods for weighing liquid components and solutions. In addition, it is an efficient and clean technique.

How to Weigh by Difference With AXP365 Weighing & Dispensing™

The AXP365 Weighing & Dispensing™ module of AX for Pharma 365™ provides a full range of weighing methods to satisfy every user and every need, including weighing by difference.

To properly weigh your substance by difference, here are the steps you should follow:

  1. Get the container with the material you need to weigh.
  2. Put the container on the scale. The scale screen and the AXP365 Weighing and Dispensing™ application will display the total weight of the container you put on the scale (W1).
  3. Transfer the required amount of material into your vessel. The scale screen will display the weight that remained on it (W2), but the AXP365 Weighing & Dispensing™ application will show you the quantity you removed—the target quantity you need (W3).

The target quantity is obtained with the following calculation: W3 = W1 – W2.

The AXP365 Weighing & Dispensing™ module allows you to choose the weighing-by-difference method and set the appropriate parameters (e.g., tolerance range, scale precision) to perform your weighing operations in the most efficient, clean, and accurate way.

To learn more about AX for Pharma 365™ and how it helps pharmaceutical companies reduce errors and improve accuracy, contact us today.