Campbell Scientific CR3000 Micrologger - Manual (Page 296)

Section 8. Operation
296
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 self-
calibration 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
Descriptions of Status Table Elements
Status Table
Element Differential (Diff)
Single-Ended (SE)
Offset or Gain
±mV Input
Range
Integration
CalGain(1) Gain 5000 250 ms
CalGain(2) Gain 1000 250 ms
CalGain(3) Gain 200 250 ms
CalGain(4) Gain 50 250 ms
CalGain(5) Gain 20 250 ms