Campbell Scientific CR6 CR6 Measurement and Control System - Page 309

Single-Ended Measurements - Details

Page 309 highlights

Section 8. Operation Measurement Rates (p. 230). The maximum conversion rate is 93750 conversions per second (93.750 kHz) when repeating measurements on a single terminal (burst mode), and TBD measurements per second (TBD kHz) when multiplexing between input channels. Table 61. CRBasic Parameters Varying Measurement Sequence and Timing CRBasic Parameter Description MeasOfs Correct ground offset on single-ended measurements. SettlingTime Sensor input settling time. fN1 First notch frequency RevDiff Reverse high and low differential inputs. RevEx Reverse polarity of excitation voltage. First Notch Frequency (Digital Filter) The A-to-D conversion is accompanied by digital filtering which serves two purposes: • Arrive as close as possible to the true input signal • Filter out measurement noise at specific frequencies, the most common being noise at 50 Hz or 60 Hz, which originate from mains-power lines. Filtering time is inversely proportional to the frequency being filtered. Minimizing filtering time may be preferred at times to, • minimize time skew between successive measurements. • maximize throughput rate. • maximize life of the CR6 power supply. • minimize polarization of polar sensors such as those for measuring conductivity, soil moisture, or leaf wetness. Polarization may cause measurement errors or sensor degradation. • improve accuracy of an LVDT measurement. The induced voltage in an LVDT decays with time as current in the primary coil shifts from the inductor to the series resistance; a long filtering time may result in most of signal decaying before the measurement is complete. Single-Ended Measurements - Details Reading List: • Single-Ended Measurements - Overview (p. 59) • Single-Ended Measurements - Details (p. 309) With reference to the figure Programmable Gain Input Amplifier (PGIA) (p. 308), during a single-ended measurement, the high signal is routed to V+. V- is automatically connected internally to signal ground with the low signal tied to 309

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Section 8.
Operation
Measurement Rates
(p. 230).
The maximum conversion rate is 93750 conversions
per second (93.750 kHz) when repeating measurements on a single terminal (burst
mode), and TBD measurements per second (TBD kHz) when multiplexing
between input channels.
Table 61.
CRBasic Parameters Varying Measurement Sequence and
Timing
CRBasic Parameter
Description
MeasOfs
Correct ground offset on single-ended measurements.
SettlingTime
Sensor input settling time.
f
N1
First notch frequency
RevDiff
Reverse high and low differential inputs.
RevEx
Reverse polarity of excitation voltage.
First Notch Frequency (Digital Filter)
The A-to-D conversion is accompanied by digital filtering which serves two
purposes:
Arrive as close as possible to the true input signal
Filter out measurement noise at specific frequencies, the most common being
noise at 50 Hz or 60 Hz, which originate from mains-power lines.
Filtering time is inversely proportional to the frequency being filtered.
Minimizing filtering time may be preferred at times to,
minimize time skew between successive measurements.
maximize throughput rate.
maximize life of the CR6 power supply.
minimize polarization of polar sensors such as those for measuring
conductivity, soil moisture, or leaf wetness.
Polarization may cause
measurement errors or sensor degradation.
improve accuracy of an LVDT measurement.
The induced voltage in an
LVDT decays with time as current in the primary coil shifts from the inductor
to the series resistance; a long filtering time may result in most of signal
decaying before the measurement is complete.
Single-Ended Measurements — Details
Reading List:
Single-Ended Measurements — Overview
(p. 59)
Single-Ended Measurements — Details
(p. 309)
With reference to the figure
Programmable Gain Input Amplifier (PGIA)
(p. 308),
during a single-ended measurement, the high signal is routed to V+.
V– is
automatically connected internally to signal ground with the low signal tied to
309