Specifications

Chapter 3: General Considerations
Weighing System Performance
(12/99) 3-7
Hysteresis Errors
Hysteresis is a scale's ability to repeat measurements as weights are added and
removed. Figure 3-4 shows a typical hysteresis error. The scale is accurate at zero and
at full load. When weight is gradually added to the scale, the curve drifts downward and
the scale displays readings that are too low. When a load is placed on the scale and
then the weight is gradually decreased, the curve drifts upward and displays readings
that are too high. Hysteresis is measured from the actual linearity curves shown in the
graph. It represents an energy loss and is a problem found only in electronic scales, not
in mechanical scales. You should take steps to minimize linearity and hysteresis errors
in batching, filling, and counting scale applications, especially when the full range of the
scale is used. A scale can also display high readings when weight is added and low
readings when weight is removed. But those errors would most likely be caused by
creep or a mechanical problem, rather than by hysteresis.
Counts
1,000
800
600
400
200
0
Half Load
(50% Capacity)
Full Load
(100% Capacity)
Hysteresis Error
Ideal
Actual
Hysteresis
Figure 3-4: Hysteresis Error
Repeatability Errors
Repeatability is a scale's ability to repeat the same reading when a known weight is
applied and removed several times. It is usually expressed as the maximum difference
between any two readings taken in the same way and as a percentage of full load. For
example, suppose the same 2,500-pound weight is placed on a 5,000-pound scale
100 times, with 2,501 being the highest reading and 2,500 being the lowest. The
repeatability is 0.02% (1/5,000) of the scale’s rated capacity (R.C.).