Calibration
and Unit Scaling
There can be some confusion between the function of the
Calibration Offset & Gain and the Units & Scaling Offset & Gain as used in the
Omnilog Software.
Calibration is used to
correct readings to their true values. If a Temperature sensor is reading 0.3° C low then
calibration is used to take account of this and display the correct reading.
Scaling is used to change correct readings to other Units. If
the logger is reading in ° C we can use the Scaling Offset and Gain to convert the
readings to ° F.
Calibration Gain and Offset
These are used to convert the A2D converter and counter readings to SI Units.
As much as possible we try to convert everything to SI units then Scale the readings to
whatever the user requires. There are five exceptions we have made because the SI units
are of inconvenient scale. These are:
1... Temperature we use ° C not ° K
2... Distance we use millimeters not meters
3... Pressure we use hectaPascals not Pascals
4... For a milliVolt logger we use milliVolts not Volts
5... For a 20mA channel we use milliAmps not amps
There are tables of equations in the Omnilog software
that convert the readings from the logger to SI Units (or preferred units). There can be
small errors in these readings because of small inconsistencies in the sensors and
electronic components used in the loggers. Calibration procedures minimize these small
errors even further.
Scale Gain and offset
These are used to convert the SI units (or our preferred units as listed above) to the
users required units.
So for example:
A 4-20mA channel will be calibrated so that the Calibration Gain and Offset will give the
correct result in mA. The Scale Gain and Offset can be used to convert the mA's to any
other units the user may want.
Another example:
Temperature Logger - the Calibration Gain and Offset will give a reading in ° C - the
Scale Offset and Gain can be used to scale this to ° F or ° K.
This scaling can be done automatically by clicking the
Select button in the Scale box and selecting the required units. In the case of the rain
gauge the Calibration offset and gain are used to get the logger reading in mm. 0.5mm per
tip therefore 2 tips per mm therefore Gain of 0.5 The Scale Offset and Gain could be used
to read in meters or feet or yards of kilometers or miles or even fathoms if the user
requires. The Select button will only give the common conversions and as feet and meters
of rain are uncommon the only options available are inches and tips.
