Recall the linear equation that describes the response of any linear instrument:
y = mx + b
Where:
y = output signal of the instrument
m = value of the span
x = Input signal of the instrument
b = value of zero
A zero offset error in a calibration results in a gap or vertical displacement of the graph of the equation, which is equivalent to modify the value of b of the equation. This bug affects all the points or calibration values in the same way, causing the same percentage of error in all points or values in the range of the instrument.
If a transmitter has a zero calibration error, this error can be corrected by carefully adjusting the "zero" up to the ideal response, essentially alter the value of b of linear equations.
An offset error in a calibration span causes the variation of the slope of the function, which is equivalent to altering the value of m in the linear equation. This error effect unevenly in different values or points across the range of the instrument.
If a transmitter has a span calibration error, this error can be corrected by carefully adjusting the span to achieve an ideal response, essentially alter the value of m in the linear equation.
A linearity error in a calibration funcón causes the response of the instrument ceases to be a straight line. This type of error is not directly related to zero mismatches (b) or span (m) because the above equation describes only straight lines.
Some tools provide the ability to adjust the linearity response, then this parameter should be changed with extreme care. The linearity adjustment behavior is unique to each instrument model and therefore we should consult the manufacturer's documentation for details on how this parameter works exactly. If the instrument does not provide the ability to modify its linearity, the best we can do about this type of error is "error divir or break" between high and low ends of the range, so the absolute maximum error at any point of the range will be minimized.
A hysteresis error in a calibration occurs when the instrument's response in points or different values determined by increasing the input signal to decrease the input signal. The only way to detect this type of error is to test the up-down calibration is to take note of certain values to an increase of input signal and buy them with the same values but decreasing the input signal.
Hysteresis errors are almost always caused by mechanical friction sensor (and / or a loss of coupling between mechanical) and Bourdon tubes, bellows, diaphragms, pivots, etc.. Friction always acts in the opposite direction of relative motion. Hysteresis errors can be rectified simply by making adjustments to the instrument calibration - usually to replace defective parts or fix problems in the mechanism coupling the instrument.
In practice, the most common errors are calibration problems cambinación zero, span, linearity and hysteresis.
