What Does Linearity Mean in a Balance or Scale?

In reference to balances and scales, linearity relates to how precisely a device is calibrated and, therefore, how accurate its measurements are. Most measuring devices use linearity to help determine whether it is functioning correctly and within the suggested margins of error. When a balance or scale deviates too far from linearity and functions outside its normal margin of error, this indicates a need for calibration.

Balance in Lab

“I often see linearity quoted as part of a balance or scale specification, but what does it mean to me?”

Balances and scales must be very precise instruments. Like all instruments, they perform within stated parameters. One common parameter for balances and scales relates to linearity.

Figure 1

Basically, linearity refers to a deviation or lack of deviation from a straight line. When discussing the accuracy of a scale or balance, perfect linearity would mean that the actual weight of an item and the displayed weight were equal. It would mean no error, even a slight difference, between the actual and displayed weight.

If we draw a graph with weight at one side and displayed value at the other, a purely linear balance would show a straight 45° line from the zero point up to full capacity. Each time the load increases, the displayed value increases at the exact same rate, thus giving the straight line. See Figure 1. Please note that the errors in the graphs below are exaggerated to provide clarity.

Figure 1

Figure 1

Figure 2

In Figure 2, We see an example of the allowed linearity of an analytical balance of 200 g with an allowable linearity of ± 0.0002 g. This example shows the error allowed around the “perfect” linearity. The green shaded area represents the permissible error allowed, as small error windows are commonly assessed and factored when using scales and balances.

F2 - area-linearity-graph

Figure 2

Figure 3

In Figure 3, We show the typical linearity of a 200 g balance, with a slight positive error (0.0001 g) below 100 g and a slight negative error over 100 g of 0.0002 g. This balance is just within specification.

F3 - acc-linearity-graph

Figure 3

Figure 4

In Figure 4, We see a balance that is just outside the tolerance allowed, as the curve of the displayed value exceeds the ±0.0002 g permissible error.

F4 - uunac-linearity-graph

Figure 4

Conclusion

In order to ensure that their products are weighing accurately within an acceptable margin of error, manufacturers and scale dealers have the ability to correct errors in linearization by adjusting the balance with test weights at regular intervals of the capacity. This is not calibration that can be performed with a single weight, provided that the balance has been correctly linearized. Linearization should not be attempted without a specialist’s knowledge and the correct test weights.

Request A Quote

Customer Information
Shipping Address
Billing Address

Will you need a lift gate? *

(For deliveries requiring a LTL truck and the customer does not have a dock door)

Would you like to add shipping amount to quote? *

Are you tax exempt? *

(If you are tax exempt, please email your tax exemption form to [email protected])

Upload PDF: