Campbell Scientific CR6 CR6 Measurement and Control System - Page 326
Read More, VoltSe, VoltDiff, VoltSE
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Section 8. Operation 5. Reverse the excitation, settle, measure There are four delays per measurement. The CR6 processes the four submeasurements into the reported measurement. In cases of excitation reversal, excitation time for each polarity is exactly the same to ensure that ionic sensors do not polarize with repetitive measurements. Read More A white paper entitled "The Benefits of Input Reversal and Excitation Reversal for Voltage Measurements" is available at www.campbellsci.com. Ground Reference Offset Voltage When MeasOff is enabled (= True), the CR6 measures the offset voltage of the ground reference prior to each VoltSe() or TCSe() measurement. This offset voltage is subtracted from the subsequent measurement. From Background Calibration If RevDiff, RevEx, or MeasOff is disabled (= False) in a measurement instruction, offset voltage compensation is still performed, albeit less effectively, by using measurements from the automatic background calibration. Disabling RevDiff, RevEx, or MeasOff speeds up measurement time; however, the increase in speed comes at the cost of accuracy because, 1 RevDiff, RevEx, and MeasOff are more effective techniques 2 background calibrations are performed only periodically, so more time skew occurs between the background calibration offsets and the measurements to which they are applied. Note When measurement duration must be minimal to maximize measurement frequency, consider disabling RevDiff, RevEx, and MeasOff when CR6 module temperatures and return currents are slow to change. Time Skew Between Measurements Time skew between consecutive voltage measurements is a function of settling times, A-to-D conversion, and the number entered into the Reps parameter of the VoltDiff() or VoltSE() instruction. A close approximation is: time skew = settling time + A-to-D conversion time1 + reps/no reps2 1A-to-D (analog-to-digital) conversion time = TBD µs 2If Reps > 1 (i.e., multiple measurements by a single instruction), no additional time is required. If Reps = 1 in consecutive voltage instructions, add 15 µs per instruction. Voltage Measurement Time This section not yet available. Kevin R to provide content. 326