Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 274)

Section 8. Operation
274
Table 51. CRBasic Parameters Varying Measurement Sequence and
Timing
CRBasic Parameter Description
MeasOfs Correct ground offset on single-ended measurements.
RevDiff Reverse high and low differential inputs.
SettlingTime Sensor input settling time.
Integ Duration of input signal integration.
RevEx Reverse polarity of excitation voltage.
8.1.2.4 Measurement Accuracy
CR800 analog-measurement error is calculated as
Error = Gain Error (%) + Offset Error
Gain error is expressed as ±% of reading and is a function of CR800 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 CR800 Specifications
).
Figure Voltage Measurement Accuracy (0° to 40°C)
(p. 275)
illustrates that as
magnitude of input voltage decreases, measurement error decreases.
Note The accuracy specification includes only the CR800 contribution to
measurement error. It does not include the error of sensors.
For example, assume the following (see CR800 Specifications ):
• Input Voltage: 2500 mV
• Programmed Input Voltage Range: ±2500 mV (
mV2500 )
• Programmed Measurement Instruction: VoltDiff()
• Input Measurement Reversal:
True
• CR800 Temperature: Between 0°C and 40°C
Accuracy of the measurement is calculated as follows:
Error = Gain Error + Offset Error,