Campbell Scientific CR3000 CR3000 Micrologger - Page 296

Section 8. Operation If this rate of update for measurement channels is too slow, the Calibrate() instruction can be used. The Calibrate() instruction computes the necessary G and B values every scan without any low-pass filtering. For a VoltSe() instruction, B is determined as part of self-calibration only if the parameter MeasOff = 0. An exception is B for VoltSe() on the ±2500 mV input range with 250 μs integration, which is always determined in self-calibration for use internally. For a VoltDiff() instruction, B is determined as part of selfcalibration only if the parameter RevDiff = 0. VoltSe() and VoltDiff() instructions, on a given input range with the same integration durations, utilize the same G values but different B values. The 5 input-voltage ranges (±5000 mV, ±1000 mV, ±200 mV, ±50 mV, ±20 mV) along with the three different integration durations (250 μs, 50-Hz half-cycle, and 60-Hz half-cycle) result in a maximum of 15 different gains (G), and 15 offsets for VoltSe() measurements (B), and 15 offsets for VoltDiff() measurements (B) to be determined during CR3000 self-calibration (maximum of 45 values). These values can be viewed in the Status table, with entries identified as listed in table Status Table Calibration Entries (p. 296). Automatic self-calibration can be overridden with the Calibrate() instruction, which forces a calibration for each execution, and does not employ any low-pass filtering on the newly determined G and B values. There are two parameters associated with the Calibrate() instruction: CalRange and Dest. CalRange determines whether to calibrate only the necessary input ranges for a given CRBasic program (CalRange = 0) or to calibrate all input ranges (CalRange ≠ 0). The Dest parameter should be of sufficient dimension for all the returned G and B values, which is a minimum of two for the automatic self-calibration of VoltSE() including B (offset) for the ±5000 mV input range with first 250 µs integration, and a maximum of 45 for all possible integration durations and input-voltage ranges chosen. An example use of the Calibrate() instruction programmed to calibrate all input ranges is given as: 'Calibrate(Dest,Range) Calibrate(cal(1),true) where Dest is an array of 45 variables, and Range ≠ 0 to calibrate all input ranges. Results of this command are listed in the table Calibrate() Instruction Results (p. 298). Table 61. Status Table Calibration Entries Status Table Element CalGain(1) CalGain(2) CalGain(3) CalGain(4) CalGain(5) Differential (Diff) Single-Ended (SE) Descriptions of Status Table Elements Offset or Gain Gain Gain Gain Gain Gain ±mV Input Range 5000 1000 200 50 20 Integration 250 ms 250 ms 250 ms 250 ms 250 ms 296