Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 163

FieldCalStrain, StrainCalc

Page 163 highlights

Section 7. Installation 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 adjusted gage factor (GFadj), which is then used as the gage factor in StrainCalc(). GF is stored in the CAL file and continues to be used in subsequent calibrations. Non-linearity of the bridge is compensated for by selecting a shunt resistor with a value that best simulates a measurement near the range of measurements to be made. Strain-gage manufacturers typically specify and supply a range of resistors available for shunt calibration. 3. Shunt calibration verifies the function of the CR800. 4. The zero function of FieldCalStrain() allows the user to set a particular strain as an arbitrary zero, if desired. Zeroing is normally done after the shunt calibration. Zero and shunt options can be combined through a single CR800 program. The following program is provided to demonstrate use of FieldCalStrain() features. If a strain gage configured as shown in figure Quarter-Bridge StrainGage Schematic (p. 164) is not available, strain signals can be simulated by building the simple circuit, substituting a 1000-Ω potentiometer for the strain gage. To reset calibration tests, use the support software File Control (p. 431) menu to delete .cal files, and then send the demonstration program again to the CR800. Case: A 1000-Ω strain gage is placed into a resistive bridge at position R1. The resulting circuit is a quarter-bridge strain gage with alternate shunt-resistor (Rc) positions shown. Gage specifications indicate that the gage factor is 2.0 and that with a 249-kΩ shunt, measurement should be about 2000 microstrain. Send CRBasic example FieldCalStrain() Calibration Demo (p. 164) as a program to a CR800 datalogger. 163

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Section 7.
Installation
163
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
adjusted gage factor (GF
adj
), which is then used as the gage factor in
StrainCalc()
.
GF is stored in the CAL file and continues to be used in
subsequent calibrations.
Non-linearity of the bridge is compensated for by
selecting a shunt resistor with a value that best simulates a measurement near
the range of measurements to be made.
Strain-gage manufacturers typically
specify and supply a range of resistors available for shunt calibration.
3.
Shunt calibration verifies the function of the CR800.
4. The zero function of
FieldCalStrain()
allows the user to set a particular strain
as an arbitrary zero, if desired. Zeroing is normally done after the shunt
calibration.
Zero and shunt options can be combined through a single CR800 program.
The following program is provided to demonstrate use of
FieldCalStrain()
features. If a strain gage configured as shown in figure
Quarter-Bridge Strain-
Gage Schematic
(p. 164)
is not available, strain signals can be simulated by building
the simple circuit, substituting a 1000-
potentiometer for the strain gage. To
reset calibration tests, use the support software
File Control
(p. 431)
menu to delete
.cal files, and then send the demonstration program again to the CR800.
Case
: A 1000-
strain gage is placed into a resistive bridge at position R1. The
resulting circuit is a quarter-bridge strain gage with alternate shunt-resistor (Rc)
positions shown. Gage specifications indicate that the gage factor is 2.0 and that
with a 249-k
shunt, measurement should be about 2000 microstrain.
Send CRBasic example
FieldCalStrain() Calibration Demo
(p. 164)
as a program to
a CR800 datalogger.