CR300-Series Datalogger
27
•
VoltSE()
•
BrHalf()
•
BrHalf3W
•
TCSE()
•
Therm107()
•
Therm108()
•
Therm109()
6.1.1.2 Differential Measurements
A differential measurement measures the difference in voltage between two
input terminals. For example,
DIFF
channel
1
is comprised of terminals
1H
and
1L
, with
1H
as high and
1L
as low. The CR300 has three
DIFF
terminal
pairs. The differential configuration is used with the following CRBasic
instructions:
•
VoltDiff()
•
BrFull()
•
BrFull6W()
•
BrHalf4W()
•
TCDiff()
6.1.1.3 Voltage Ranges
In general, use the smallest input range that accommodates the full-scale output
of the sensor. This results in the best measurement accuracy and resolution.
The CR300 has two input ranges for voltage measurements: –100 mV to +2500
mV, and –34 mV to +34 mV.
An approximate 10% overhead on these ranges reduces the chance of
overrange. For example, overrange on the –100 to +2500 mV input range
occurs at approximately –110 mV and 2750 mV. The CR300 indicates a
measurement overrange by returning a
NAN
(not a number) for the
measurement.
6.1.1.4 Settling Time
The settling time parameter (
SettlingTime
) is the amount of time to delay after
setting up a measurement and before making the measurement. It defaults to
500 µs, with a maximum of 50 ms and a minimum of 10 µs.
6.1.1.5 Reverse Differential
Differential measurements have the advantage of an input reversal option,
RevDiff
. When
RevDiff
is set to
True
, two differential measurements are
made, the first with a positive polarity and the second reversed. Subtraction of
opposite polarity measurements cancels some offset voltages associated with
the measurement.
6.1.1.6 First Notch Frequency
The first notch frequency (
f
N1
) determines the lowest frequency that will be
eliminated, or notched out, by a sinc filter. This filter notches out frequencies at
integer multiples of
f
N1
by averaging for a time equal to 1/
f
N1
. Thus, lower first
notch frequencies result in longer measurement times.
Содержание CR300 series
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