Campbell CR3000 Micrologger, Operator'S Manual

Page: 244 / 644

Section 7. Installation
244
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 CR3000.
4. The zero function of FieldCalStrain() allows a particular strain to be set as an
arbitrary zero, if desired. Zeroing is normally done after the shunt calibration.
Zero and shunt options can be combined ina single CRBasic program.
CRBasic example FieldCalStrain() Calibration
(p. 245)
is provided to demonstrate
use of FieldCalStrain() features. If a strain gage configured as shown in figure
Quarter-Bridge Strain Gage with RC Resistor Shunt
(p. 245)
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. 539)
menu to delete .cal files, and then send the
demonstration program again to the CR3000.
Example Case: A 1000 Ω strain gage is placed into a resistiv
e 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 micro
strain.
Send CRBasic example FieldCalStrain() Calibration
(p. 245)
as a program to a
CR3000 datalogger.
7.7.12.6.2 FieldCalStrain() Shunt Calibration Example
CRBasic example FieldCalStrain() Calibration
(p. 245)
is provided to demonstrate
use of FieldCalStrain() features. If a strain gage configured as shown in figure
Quarter-Bridge Strain Gage with RC Resistor Shunt
(p. 245)
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. 539)
menu to delete .cal files, and then send the
demonstration program again to the CR3000.
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
(p. 245)
as a program to a
CR3000 datalogger.