How do I determine the accuracy of my weighing system?

The definition of accuracy for your weighing system is dependant on how you use it.  For instance, if you are making your measurement only after you add weight to your system, you should use the non-linearity specification of your Hardy load cells. All Hardy Advantage load cells are rated with a C3 accuracy class.

If you are making your measurement only after you remove weight from your system, you should use the Hysteresis specification of your Hardy load cells.

If you make a measurement after adding or removing weight from your system, you should use the non-linearity and Hysteresis error specification combined.

For example, using a 16,500 lb Hardy load cell:
Non-Linearity 0.018% = 2.97 lb or approximately 1 in 5,000
Hysteresis <0.025% = 4.125 lb or approximately 1 in 4000
Combined error <0.043% = 7.095 lb or approximately 1 in 3000

The above does not including mechanical, electronic or electrically induced errors and is a worst case scenario of just the load cell error.

Before designing a system, an engineer should carefully consider  the expected accuracy and then relate this to the component accuracies making up the system. No physical measuring system can be completely accurate. An error band must be defined for a system which gives an indication of expected deviations from true value. The parameters under which this applies must also be clear and concise. Accuracy terms such as "1 part in 5000" are commonly used.

The accuracy of your Hardy controllers are measured by the display resolution, and is between one part on one million to one part in eight million. This negligible error is due to the superior design of our analog to digital circuitry. The majority of the error you will experience with your Hardy weighing system will have an external root cause. Mechanical and electrical issues that can and will affect your system accuracy reading are EMI/RFI noise, scale binding, correct load cell placement and balance, etc. There are also environmental considerations to take into account such as variations in humidity, temperature, and wind.

To determine the accuracy of your weighing system you will have to find the non-linearity and Hysteresis specifications for your load cells, verify that there are no other mechanical issues affecting your accuracy reading, and allow for gravity correction.

As you can see, calculating true weigh system accuracy is very difficult, and many customers do not know what they really require from their system. They often request a "system to be as accurate as possible".  Proper installation is critical to maximize a systems accuracy, but other considerations such as connecting pipes and conduits must be taken into account. One thing is certain, good load cells do not make a poor system good, but poor load cells can only make a good system poor. Hardy Instrument Controllers and Load Sensors are considered by many to be the most accurate available in today's process weighing market.

The relationship between load cell, instrument, system resolution, and accuracy is one of the most misunderstood in the weighing industry. A good working knowledge of the following terms is required when calculating the accuracy of your weighing system:

LOAD SENSOR ACCURACY: This term is commonly used as the inverse of the term "combined error". A standard combined error for a typical load sensor is 0.03% of full scale. Using a 300 lb example the accuracy would be 0.09 pounds. Where absolute accuracy is the main system requirement, load sensor accuracy is the primary limiting f