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TOTAL ACCURACY vs. THE STANDARD ACCURACY DEFINITION
Rev. C
Total Accuracy Transducers corporation use total accuracy to define signal accuracy. Total accuracy as used by TAT, includes all possible error sources over all specified environments in any reasonable combination.
The standard definition of accuracy (not used by TAT) is the combination of non-linearity, hysteresis, and non-repeatability. Non-repeatability is taken over a short period of time under constant temperature and other operating conditions.
Usually non-linearity is constant over time and temperature and other operating conditions.
Usually hysteresis is fairly constant, but it can change with extended time, especially with the presence of moisture with a device, which has a critical glue joint, which can have a significant effect on the signal.
Non-repeatability is defined as the maximum difference between readings when made under identical loading and environmental conditions. Clearly, this definition does not include temperature effects. It also does not include signal errors caused by many other sources including power supply variation, electrical grounding sensitivity, mounting stress effects, load misalignment.
Most important of all, non-repeatability also does not include the effects of extended time periods of loading or between calibration intervals.
A user who buys a load cell using only the standard definition of accuracy will usually not get anything like the total accuracy they expect if they think of "accuracy" as commonly used as meaning total accuracy.
Additionally, the accuracy of a system which starts off with a standard analog strain load cell and uses and amplifier and digitizer will certainly have a poorer accuracy at the digital signal level than that specified at the load cell only level where there is only a low level analog voltage signal.
When TAT specifies total accuracy, that accuracy is for the entire system at the final digital signal level and includes all effects of all system components. Such a type of specification is the only way the user can have a high confidence that they will get the real accuracy they expect.
Purchasers of any transducer should get the supplier to precisely define the total accuracy which is warrantied in the application, over extended time and when exposed to the environmental conditions which are likely to occur.
Copyright © 1997-2000 Total Accuracy Transducers Incorporated. All Rights Reserved.
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