Section 8. Operation
Note
Error discussed in this section and error-related specifications of the
CR1000 do not include error introduced by the sensor or by the transmission of
the sensor signal to the CR1000.
The accuracy specifications for ratiometric-resistance measurements are
summarized in the tables
Ratiometric-Resistance Measurement Accuracy
(p. 342).
Table 72.
Ratiometric-Resistance Measurement Accuracy
–25 to 50 °C
±(0.04% of voltage measu offset)
1
1
Voltage measurement is variable V
1
or V
2
in the table
Resistive-Bridge Circuits with Voltage
Excitation
(p. 338).
Offset is the same as that for simple analog-voltage measurements. See the
table
Analog-Voltage Measurement Offsets
(p. 313).
Assumptions that support the ratiometric-accuracy specification include:
•
CR1000 is within factory calibration specification.
•
Excitation voltages less than 1000 mV are reversed during the excitation
phase of the measurement.
•
Effects due to the following are not included in the specification:
o
Bridge-resistor errors
o
Sensor noise
o
Measurement noise
For a tighter treatment of the accuracy of ratiometric measurements, consult the
technical paper
Estimating Measurement Accuracy for Ratiometric Measurement
Instructions
., which should be available at
www.campbellsci.com/app-notes
http://www.campbellsci.com/app-notes
) in June of 2015.
8.1.2.5 Strain Measurements — Details
Related Topics:
•
Strain Measurements — Overview
(p. 68)
•
Strain Measurements — Details
(p. 342)
•
FieldCalStrain() Examples
(p. 223)
A principal use of the four-wire full bridge is the measurement of strain gages in
structural stress analysis.
StrainCalc()
calculates microstrain (
µ
ε)
from the
formula for the particular strain bridge configuration used. All strain gages
supported by
StrainCalc()
use the full-bridge schematic. In strain-gage parlance,
'quarter-bridge', 'half-bridge' and 'full-bridge' refer to the number of active
elements in the full-bridge schematic. In other words, a quarter-bridge strain gage
has one active element, a half-bridge has two, and a full-bridge has four.
StrainCalc()
requires a bridge-configuration code. The table
StrainCalc()
Instruction Equations
(p. 343)
shows the equation used by each configuration code.
Each code can be preceded by a dash (
-
). Use a code without the dash when the
bridge is configured so the output decreases with increasing strain. Use a dashed
code when the bridge is configured so the output increases with increasing strain.
In the equations in table
StrainCalc()
Instruction Equations
(p. 343),
a dashed code
342
Summary of Contents for CR1000
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