Section 8. Operation
21 segments. So, (21 segments) • (4 s / segment) = 84 s per complete auto self-
calibration. The worst-case is (91 segments) • (4 s / segment) = 364 s per
complete auto self-calibration.
During instrument power-up, the CR800 computes calibration coefficients by
averaging ten complete sets of auto self-calibration measurements. After power
up, newly determined G and B values are low-pass filtered as follows:
Next_Value = (1/5) • (new value) + (4/5) • (old value)
This results in the following settling percentages:
• 20% for 1 new value,
• 49% for 3 new values
• 67% for 5 new values
• 89% for 10 new values
• 96% for 14 new values
If this rate of update 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 auto self-calibration only if
the parameter MeasOff = 0. An exception is B for VoltSe() on the ±2500 input
range with a 250 µs integration, which is always determined in auto self-
calibration for use internally. For a VoltDiff() instruction, B is determined as part
of auto self-calibration only if the parameter RevDiff = 0.
VoltSe() and VoltDiff() instructions, on a given input range with the same
integration durations, use the same G values but different B values. The six input-
voltage ranges (±5000 mV, ±2500 mV, ±250 mV, and ±25 mV), in combination
with the three most common integration durations (250 µs, 50 Hz half-cycle, and
60 Hz half-cycle) result in a maximum of 18 different gains (G), and 18 offsets for
VoltSe() measurements (B), and 18 offsets for VoltDiff() measurements (B) to be
determined during auto self-calibration (maximum of 54 values). These values
can be viewed in the Status table, with entries identified as listed in table
CalGain() Field Descriptions
(p. 339)
Auto self-calibration can be overridden with the Calibrate() instruction, which
forces a calibration for each execution, and does not employ low-pass filtering on
the newly determined G and B values. The Calibrate() instruction has two
parameters: 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 returned G and B values, which is a minimum of two
for the auto self-calibration of VoltSE() including B (offset) for the ±2500 mV
input range with first 250 µs integration, and a maximum of 54 for all input-
voltage ranges used and possible integration durations.
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