Campbell Scientific CR1000KD CR1000 Measurement and Control System - Page 278

Section 8. Operation 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 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