'PERFORM A MULTIPLIER CALIBRATION.
'Start by setting variable CalMode = 1. Finished when variable CalMode = 6.
'FieldCal(Function, MeasureVar, Reps, MultVar, OffsetVar, Mode, KnownVar, Index, Avg)
FieldCal(3,WC,1,WCMultiplier,0,CalMode,KnownWC,1,30)
'If there was a calibration, store it into data table CalHist
CallTable(CalHist)
NextScan
7.9.12.5.5 FieldCal() Zero Basis (Opt 4) Example -- 8 10 30
Zero-basis calibration (FieldCal() instruction Option 4) is designed for use in
static vibrating-wire measurements. For more information, refer to these
manuals available at www.campbellsci.com:
AVW200-Series Two-Channel VSPECT Vibrating-Wire Measurement Device
CR6 Measurement and Control Datalogger Operators Manual
7.9.12.6 Field Calibration Strain Examples
Related Topics:
• Strain Measurements — Overview (p. 68)
• Strain Measurements — Details
(p. 342)
• FieldCalStrain() Examples
(p. 223)
Strain-gage systems consist of one or more strain gages, a resistive bridge in
which the gage resides, and a measurement device such as the CR1000
datalogger. The FieldCalStrain() instruction facilitates shunt calibration of
strain-gage systems and is designed exclusively for strain applications wherein
microstrain is the unit of measure. The FieldCal() instruction (FieldCal()
Examples
(p. 213) ) is typically used in non-microstrain applications.
Shunt calibration of strain-gage systems is common practice. However, the
technique provides many opportunities for misapplication and misinterpretation.
This section is not intended to be a primer on shunt-calibration theory, but only to
introduce use of the technique with the CR1000 datalogger. Campbell Scientific
strongly urges users to study shunt-calibration theory from other sources. A
thorough treatment of strain gages and shunt-calibration theory is available from
Vishay using search terms such as 'micro-measurements', 'stress analysis', 'strain
gages', 'calculator list', at:
http://www.vishaypg.com
Campbell Scientific application engineers also have resources that may assist you
with strain-gage applications.
7.9.12.6.1 Field Calibration Strain Examples
1. Shunt calibration does not calibrate the strain gage itself.
2. Shunt calibration does compensate for long leads and non-linearity in the
resistive bridge. Long leads reduce sensitivity because of voltage drop.
FieldCalStrain() uses the known value of the shunt resistor to adjust the gain
(multiplier / span) to compensate. The gain adjustment (S) is incorporated by
FieldCalStrain() with the manufacturer's gage factor (GF), becoming the
223
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