Table 62. CRBasic Measurement Settling Times
SettlingTime
Argument
Integ
Argument
Resultant
Settling Time
1
1
450 µs is the minimum settling time required to meet CR1000 resolution specifications.
Settling Errors
When sensors require long lead lengths, use the following general practices to
minimize settling errors:
• Do not use wire with PVC-insulated conductors. PVC has a high dielectric
constant, which extends input settling time.
• Where possible, run excitation leads and signal leads in separate shields to
minimize transients.
• When measurement speed is not a prime consideration, additional time can be
used to ensure ample settling time. The settling time required can be
measured with the CR1000.
• In difficult cases, settling error can be measured as described in section
Measuring Settling Time
(p. 319).
Measuring Settling Time
Settling time for a particular sensor and cable can be measured with the CR1000.
Programming a series of measurements with increasing settling times will yield
data that indicate at what settling time a further increase results in negligible
change in the measured voltage. The programmed settling time at this point
indicates the settling time needed for the sensor / cable combination.
CRBasic example Measuring Settling Time
(p. 319) presents CRBasic code to help
determine settling time for a pressure transducer using a high-capacitance
semiconductor. The code consists of a series of full-bridge measurements
(BrFull()) with increasing settling times. The pressure transducer is placed in
steady-state conditions so changes in measured voltage are attributable to settling
time rather than changes in pressure. Reviewing the section Programming
(p. 122)
may help in understanding the CRBasic code in the example.
The first six measurements are shown in table First Six Values of Settling-Time
Data
(p. 321). Each trace in figure Settling Time for Pressure Transducer (p. 321)
contains all twenty PT() mV/V values (left axis) for a given record number, along
with an average value showing the measurements as percent of final reading (right
axis). The reading has settled to 99.5% of the final value by the fourteenth
measurement, which is contained in variable PT(14). This is suitable accuracy for
the application, so a settling time of 1400 µs is determined to be adequate.
319
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