CR1000 Manual - Campbell Scientific

Section 8. Operation
Table 51. CRBasic Parameters Varying Measurement Sequence and
Timing
CRBasic Parameter
MeasOfs
RevDiff
SettlingTime
Integ
RevEx
Description
Correct ground offset on single-ended measurements.
Reverse high and low differential inputs.
Sensor input settling time.
Duration of input signal integration.
Reverse polarity of excitation voltage.
8.1.2.4 Measurement Accuracy
CR1000 analog-measurement error is calculated as
Error = Gain Error (%) + Offset Error
Gain error is expressed as ±% of reading and is a function of CR1000
temperature. Between 0°C and 40°C, gain error is ±0.06% of input voltage. This
gain error assumes factory recalibration every two years.
Offset error depends on measurement type and input range. For differential
measurements with input reversal,
Offset Error = 1.5 • Basic Resolution + 1.0 µV
where
Basic Resolution is the published resolution of the programmed input
voltage range (see CR1000 Specifications ).
Figure Voltage Measurement Accuracy (0° to 40°C) (p. 279) illustrates that as
magnitude of input voltage decreases, measurement error decreases.
Note The accuracy specification includes only the CR1000 contribution to
measurement error. It does not include the error of sensors.
For example, assume the following (see CR1000 Specifications ):
• Input Voltage: 2500 mV
• Programmed Input Voltage Range: ±2500 mV (mV2500)
• Programmed Measurement Instruction: VoltDiff()
• Input Measurement Reversal: True
• CR1000 Temperature: Between 0°C and 40°C
Accuracy of the measurement is calculated as follows:
Error = Gain Error + Offset Error,
278