CR300-Series Datalogger
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• 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.
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