Campbell CR6 Series, Руководство оператора

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Section 8. Operation
426
The rate at which the signal settles is determined by the input settling time
constant, which is a function of both the source resistance and fixed-input
capacitance (4.7 nfd) of the CR6.
Rise and decay waveforms are exponential. Figure Input Voltage Rise and
Transient Decay
(p. 393)
shows rising and decaying waveforms settling closer to the
true signal magnitude, V
so
. The SettlingTime parameter of an analog
measurement instruction allows tailoring of measurement instruction settling
times with 100 µs resolution up to 600000 µs.
Settling times are listed in table CRBasic Measurement Settling Times
(p. 393).
Default settling times (those resulting when SettlingTime = 0 ) provide sufficient
settling in most cases. Additional settling time is often programmed when
measuring high-resistance (high-impedance) sensors or when sensors connect to
the input terminals by long leads.
Measurement time of a given instruction increases with increasing settling time.
For example, a 1 ms increase in settling time for a bridge instruction with input
reversal and excitation reversal results in a 4 ms increase in time for the CR6 to
perform the instruction.
FIGURE 91: Input voltage rise and transient decay
b
CRBasic Measurement Settling Times
SettlingTime
Argument Resultant Settling Time
1
0 500 µs
integer between 100 and 600000 ,
inclusive
μs entered in SettlingTime
argument
1
500 µs is the default voltage measurement settling time.
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.