Specifications

Section 11. Programming Resource Library
11-10
BeginProg
Multiplier = 1
Offset = 0
KnownWC = 0
LoadFieldCal(true) 'Load the CAL File, if possible
Scan(100,mSec,0,0)
'Simulate measurement by exciting channel Vx/EX1
ExciteV(Vx1,mV,0)
'Make the calibrated measurement
VoltSE(RelH2OContent,1,mV2500,8,1,0,250,Multiplier,Offset)
'Perform a calibration if CalMode = 1
FieldCal(3,RelH2OContent,1,Multiplier,Offset,CalMode,KnownWC,1,30)
'If there was a calibration, store it into a data table
CallTable(CalHist)
NextScan
EndProg
11.1.6 FieldCalStrain() Demonstration Program
Strain gage systems consist of one or more strain gages, a Wheatstone 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 (Section 11.1.5
Fi
eldCal() Demonstration Programs) 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 at:
http://www.vishay.com/brands/measurements_group/guide/indexes/tn_index.htm
Campbell Scientific applications engineers also have resources that may assists
users with strain gage applications.
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
Wheatstone bridge. Long leads reduce sensitivity because of voltage drop.