Kistler 9323AAA - Page 72

Press Force Sensor
Type 9323AA, 9323A, 9333A, 9343A, 9363A, 9383A, 9393A
Page 70 9323A_002-476e-11.24
Best straight line – mathematical definition
The minimization of maximum deviation is known as
Chebyshev’s approximation. The best straight line is
determined as follows:
 x = measurand (reference)
 Q = sensor charge signal or output signal from the
charge amplifier
 Q (x) = calibration curve, rising and falling
 s = slope of the best straight lines
 Best straight line: y
i
= s x
i
(with starting value for slope s)
 Form residues: res
i
= Q
i
- y
i
 Σ
res
= res
max
+ res
min
sum min. + max. deviation
 Recursive minimization of Σ
res
= f (s) by changing s
until Σ
res
= 0
 Linearity a = res
max
= |res
min
|
Fig. 39: Best straight line, linearity and hysteresis
Hysteresis
The maximum difference in output, at any measurand
value within the specified range, when the value is
approached first increasing and then decreasing measurand
(source: ANSI/ISA-S37.1).
Note: The quartz crystal itself has a scarcely measurable
hysteresis. However, the mechanical construction of the
sensor can result in slight hysteresis. If the hysteresis is
above the specified values (in %FSO), then the sensor is
faulty or has not been correctly installed.