Campbell Scientific CR6 CR6 Measurement and Control System - Page 318

Signal-Settling Time

Page 318 highlights

Section 8. Operation Figure 85. Normalized Sinc Frequency Response Signal-Settling Time Settling time allows an analog voltage signal to settle closer to the true magnitude prior to measurement. To minimize measurement error, signal settling is needed when a signal has been affected by one or more of the following: • The small transient originating from the internal multiplexing that connects a CR6 terminal with measurement circuitry. • A relatively large transient may be induced by an adjacent excitation conductor on the signal conductor because of capacitive coupling during a bridge measurement. • 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. 319) shows rising and decaying waveforms settling closer to the true signal magnitude, Vso. 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. Default settling times (those resulting when SettlingTime = 0) provide sufficient settling in most cases. Additional settling time is often programmed when measuring highresistance (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 318

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Section 8.
Operation
Figure 85. Normalized Sinc Frequency Response
Signal-Settling Time
Settling time allows an analog voltage signal to settle closer to the true magnitude
prior to measurement.
To minimize measurement error, signal settling is needed
when a signal has been affected by one or more of the following:
The small transient originating from the internal multiplexing that connects a
CR6 terminal with measurement circuitry.
A relatively large transient may be induced by an adjacent excitation
conductor on the signal conductor because of capacitive coupling during a
bridge measurement.
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. 319)
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
.
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
318