Campbell CR3000 Micrologger, Руководство оператора

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Section 8. Operation
347
•
If the open circuit is at the end of a very long cable, the test pulse (300
mV) may not charge the cable (with its high capacitance) up to a voltage
that generates NAN or a distinct error voltage. The cable may even act as
an aerial and inject noise which also might not read as an error voltage.
•
The sensor may "object" to the test pulse being connected to its output,
even for 100 µs. There is little or no risk of damage, but the sensor
output may be caused to temporarily oscillate. Programming a longer
settling time in the CRBasic measurement instruction to allow
oscillations to decay before the A-to-D conversion may mitigate the
problem.
Range-Code Option C Over-Voltages
Input Range Over-Voltage
±
20 mV
±
50 mV
±
200 mV
300 mV
±
1000 mV 1200 mV
±5
000 mV
5200 mV
Offset Voltage Compensation
Related Topics
• Auto Self-Calibration — Overview
(p. 92)
• Auto Self-Calibration — Details
(p. 373)
• Auto Self-Calibration — Errors
(p. 515)
• Offset Voltage Compensation
(p. 347)
• Factory Calibration
(p. 89)
• Factory Calibration or Repair Procedure
(p. 500)
Summary
Measurement offset voltages are unavoidable, but can be minimized.
Offset voltages originate with:
• Ground currents
• Seebeck effect
• Residual voltage from a previous measurement
Remedies include:
• Connect power grounds to power ground terminals (G)
• Use input reveral (RevDiff = True) with differential measurements
• Automatic offset compensation for differential measurements when
RevDiff = False
• Automatic offset compensation for single-ended measurements when
MeasOff = False
• Better offset compensation when MeasOff = True
• Excitation reversal (RevEx = True)
• Longer settling times