Section 8. Operation
worst-
case is (91 segments) • (4 s / segment) = 364 s per complete self
-calibration.
During instrument power-up, the CR1000 computes calibration coefficients by
averaging ten complete sets of 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 self-calibration only if the
parameter
MeasOff
=
0
. An exception is B for
VoltSe()
on the
±
2500 input range
with a 250
µ
s 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, 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
µ
s, 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 CR1000 self-calibration (maximum of 54 values). These
values can be viewed in the
Status
table, with entries identified as listed in table
Status Table Calibration Entries
(p. 346).
Automatic 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 automatic 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.
An example use of the
Calibrate()
instruction programmed to calibrate all input
ranges is given in the following CRBasic code snip:
'Calibrate(Dest,Range)
Calibrate
(cal(1),true)
where
Dest
is an array of 54 variables, and
Range
≠
0
to calibrate all input ranges.
Results of this command are listed in the table
Calibrate()
Instruction Results
(p.
345
Summary of Contents for CR1000
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