Campbell CR3000 Micrologger, Руководство оператора

Страница: 372 / 644

Section 8. Operation
372
Measurements
• Voltage Measurement Accuracy, Self- Calibration, and Ratiometric
Measurements
• Estimating Measurement Accuracy for Ratiometric Measurement
Instructions.
Note Error discussed in this section and error-related specifications of
the CR3000 do not include error introduced by the sensor or by the
transmission of the sensor signal to the CR3000.
The accuracy specifications for ratiometric-resistance measurements are
summarized in the tables Ratiometric-Resistance Measurement Accuracy
(p. 372).
Ratiometric-Resistance Measurement Accuracy
0 to 40 °C –25 to 50 °C –40 to 85 °C
±(0.02% of voltage
measu offset)
1
±(0.025% of voltage
measu offset)
1
±(0.03% 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. 368).
Offset is the same as that for simple
analog voltage measurements. See the table Analog Voltage Measurement
Offsets
(p. 352).
Assumptions that support the ratiometric-accuracy specification include:
•
CR3000 is within factory calibration specification.
•
Excitation voltages less than 500 mV and excitation currents less than
500 µA 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
•
Resistance measured with Resistance() instruction is determined from
Vs/Ix, where excitation current Ix is measured across a 1000 Ω, ±0.005%
@ 25 ˚C, 2 ppm/˚C TCR internal resistor.
For a full treatise on the accuracy of ratiometric measurements, consult the
technical paper Estimating Measurement Accuracy for Ratiometric Measurement
Instructions at www.campbellsci.com/app-notes.