Campbell CR800 Series, Руководство оператора

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Section 7. Installation
233
7.7.12 Measurement: Fast Analog Voltage
Measurement speed requirements vary widely. The following are examples:
• An agricultural weather station measures weather and soil sensors once
every 10 seconds.
•
A station that warns of rising water in a stream bed measures at 10 Hz.
• A station measuring mechanical stress measures at 1000 Hz.
• A station measuring the temperature of a grass fire measures at 93750
Hz.
TABLE: Maximum Measurement Speeds Using VoltSE()
(p. 233)
lists maximum
speeds at which single-ended voltage inputs can be measured using the
VoltSE()
instruction. Differential measurements are slower. That fact that you can program
the CR800 to measure at these speeds, however, does not mean necessarily that
you should. The integrity of measurements begins to come into question when
fN1 , which is the reciprocal of signal integration time, is larger than 15000, and
when SettlingTime is less than 500 µs. While programming the CR800 for fast
measurements, you must balance the need for data integrity with the need for
speed.
Maximum Measurement Speeds Using VoltSE()
VoltSE() Measurement Type Maximum Speed on
n
Channels
Fast Scan() 100 Hz, n = 6
Cluster Burst
1,2
1000 Hz, n = 1
500 Hz,
n
=3
Dwell Burst
1,3 ≤ 1735 samples @ 2000 Hz,
n
= 1
1
Bursts are programmed episodes of rapid analog measurements that cannot
be maintained continuously. Input channels can be single-ended SE terminals
or differential H / L terminal pairs. Bursts require pipeline mode and may
require additional Scan() buffers. Test specific applications thoroughly before
deployment.
2
Cluster bursts loop through a series of channels, one measurement per
channel, until the programmed loop count is complete.
3
Dwell bursts sit on one channel until the programmed measurement count is
complete.
You can make fast measurements with the following instructions:
•
Single-Ended Instrucitons:
o
TCSe()
o BrHalf()