Which calibration method should I use?

There are four types of calibration, which include:

1. Hard Calibration Using Certified Weights
2. Hard Calibration Using Material Substitution
3. Hard Calibration Using Test Weights with Material Build
4. C2® Second Generation Calibration (Hardy Process Solutions instruments only)

When should I use which method?

1.) Hard Calibration Using Certified Weights:
Hardware Calibration Using Certified Weights (also called Traditional Calibration) is typically used in an environment where multiple scales are in the same process and the outputs are compared. Where a weight accuracy standard is set and that standard must comply to allow a product's release. Also when the product weighed is the same or general range. A scale is most accurate at zero and the span weight amount. To improve weighing in a particular weighing range, use that weight as the span value in the calibration procedure. Weighing 5 kg bags on a checking scale. Calibrate at zero and then span using a 5 kg test weight. This creates a very accurate scale for that target weight. Scales that measure a variety of weight use the 80 to 100% of the highest expected load as the span weight.

The practical minimum weight you should use when performing a hard calibration is 10% of load capacity.

The recommended minimum weight you should use when performing a hard calibration is 80-100% of your target load. Loading 500 lb bags, the span weight is 400 lb to 500 lb. This gives you the most accurate and repeatable weight readings.

This method uses known calibrated weights to apply a load on the load-receiving elements. Because the trace-ability of the standard is known and maintained, it is the most accurate calibration technique. Accuracies within + .02% of the applied load can be achieved with this method.  You are only as accurate as the test weights you use and the scale condition.  (Rubs, binds and poor installations reduce accuracy tremendously.

This procedure, however, may be restrictive for some industrial scales, as large capacity weights are not easily transferred to the site or are often unavailable in the field. In many other cases, the load-receiving element may not be able to accept placement of the weights, or be in a poorly or inaccessible location. An example of this would be a vessel hanging high above the factory floor or an open top vessel without any place to install test weights of a required amount.

To use the certified weights method of calibration, a set of Class "F" accuracy weights (within 0.01% of denomination) that meet the following regulations are required:
a. A total weight of 80% to 100% of the system capacity.
b. At least three weights between 10% and 100% of the system capacity to check the mid range.
c. Several low capacity weights equivalent to one or two instrument divisions.

This precaution is necessary due to the nature of a Test calibration. Test weight calibrations can hide or mask scale problems like non-linearity and binding. Without various levels of weight testing the scale health cannot be determine, just by a hardware calibration.

Most local Weights and Measures organizations have such weights available. Typical weight values are 10, 25, 50, 100, 500 and 1000 pounds. If the weighbridge is a device other than a platform, some method of loading the weights on the structure must be devised. Also insure the test weights are placed as close as possible to the center of the scale and the load is balanced. To many weights placed on one side or the other can cause a weighing moment that is not present in the normal operation of the scale. In that case material substitution would be a better calibration solution.

2.) Hard Calibration Using Material Substitution:
When certified test weights are not available or usable, accurately weighed material may be used to calibrate a system. In this method, material weighed on a secondary, calibrated scale is delivered to the site of the scale to be calibrated. The secondary calibrated scale should be of the same accuracy or greater and have a capacity approximately equal or less. A smaller scale has a finer resolution and produces a