Campbell CR800 Series - Fieldcal() Zero Basis (Opt 4) Example; Field Calibration Strain Examples; Fieldcalstrain() Shunt Calibration Concepts

Section 7. Installation
228
'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
EndProg
7.7.11.5.5 FieldCal() Zero Basis (Opt 4) Example
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
7.7.11.6 Field Calibration Strain Examples
Related Topics:
• Strain Measurements — Overview (p. 70)
• Strain Measurements — Details
(p. 343)
• FieldCalStrain() Examples
(p. 228)
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 CR800 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 (see Field Calibration Examples
(p. 217)) 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 CR800 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
7.7.11.6.1 FieldCalStrain() Shunt Calibration Concepts
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