Campbell CR3000 Micrologger, Руководство оператора

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Section 8. Operation
346
First Six Values of Settling Time Data
TIMESTAMP REC PT(1) PT(2) PT(3) PT(4) PT(5) PT(6)
Smp Smp Smp Smp Smp Smp
1/3/2000 23:34 0 0.03638599 0.03901386 0.04022673 0.04042887 0.04103531 0.04123745
1/3/2000 23:34 1 0.03658813 0.03921601 0.04002459 0.04042887 0.04103531 0.0414396
1/3/2000 23:34 2 0.03638599 0.03941815 0.04002459 0.04063102 0.04042887 0.04123745
1/3/2000 23:34 3 0.03658813 0.03941815 0.03982244 0.04042887 0.04103531 0.04103531
1/3/2000 23:34 4 0.03679027 0.03921601 0.04022673 0.04063102 0.04063102 0.04083316
Open-Input Detect
Note The information in this section is highly technical. It is not
necessary for the routine operation of the CR3000.
Summary
• An option to detect an open-input, such as a broken sensor or loose
connection, is available in the CR3000.
• The option is selected by appending a C to the Range code.
• Using this option, the result of a measurement on an open connection
will be NAN (not a number).
A useful option available to single-ended and differential measurements is the
detection of open inputs due to a broken or disconnected sensor wire. This
prevents otherwise undetectable measurement errors. Range codes appended
with C enable open-input detect for all input ranges. See TABLE: Analog Input
Voltage Ranges and Options
(p. 381).
Appending the Range code with a C results in a 50 µs internal connection of the
V+ input of the PGIA to a large over-voltage. The V– input is connected to
ground. Upon disconnecting the inputs, the true input signal is allowed to settle
and the measurement is made normally. If the associated sensor is connected, the
signal voltage is measured. If the input is open (floating), the measurement will
over-range since the injected over-voltage will still be present on the input, with
NAN as the result.
Range codes and applicable over-voltage magnitudes are found in TABLE: Range
Code Option C Over-Voltages
(p. 347).
The C option may not work, or may not work well, in the following applications:
•
If the input is not a truly open circuit, such as might occur on a wet cut
cable end, the open circuit may not be detected because the input
capacitor discharges through external leakage to ground to a normal
voltage within the settling time of the measurement. This problem is
worse when a long settling time is selected, as more time is given for the
input capacitors to discharge to a "normal" level.