Campbell Scientific CR3000 CR3000 Micrologger - Page 284

Section 8. Operation Table 53. 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 CR3000 analog-measurement error is calculated as Error = Gain Error (%) + Offset Error Gain error is expressed as ±% of reading and is a function of CR3000 temperature. Between 0°C and 40°C, gain error is ±0.04% 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 • Resolution + 1.0 µV where Basic Resolution is the published resolution of the programmed input voltage range (see CR3000 Specifications ). Figure CR3000 Voltage Measurement Accuracy (p. 285) illustrates that as magnitude of input voltage decreases, measurement error decreases. Note The accuracy specification includes only the CR3000 contribution to measurement error. It does not include the error of sensors. For example, assume the following (see CR3000 Specifications ): • Input Voltage: 5000 mV • Programmed Input Voltage Range: ±5000 mV (mV5000) • Programmed Measurement Instruction: VoltDiff() • Input Measurement Reversal: True • CR3000 Temperature: Between 0°C and 40°C Accuracy of the measurement is calculated as follows: Error = Gain Error + Offset Error, where Gain Error = ± (5000 * 0.0004) 284