voltage through external leakage to ground 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.
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If the open circuit is at the end of a very long cable, the test pulse 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.
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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 ADC may mitigate the problem.
9.10.4 Minimizing power-related artifacts
Some VAC-to-VDC power converters produce switching noise or AC ripple as an artifact of the
ac-to-dc rectification process. Excessive switching noise on the output side of a power supply can
increase measurement noise, and so increase measurement error. Noise from grid or mains
power also may be transmitted through the transformer, or induced electromagnetically from
nearby motors, heaters, or power lines.
High-quality power regulators typically reduce noise due to power regulation. Using the 50 Hz or
60 Hz first notch frequency
(f
N1
)
option for CRBasic analog input measurement instructions
often improves rejection of noise sourced from power mains. The CRBasic standard deviation
output instruction,
StdDev()
, can be used to evaluate measurement noise.
The data logger includes adjustable digital filtering, which serves two purposes:
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Arrive as close as possible to the true input signal
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Filter out measurement noise at specific frequencies, the most common being noise at 50
Hz or 60 Hz, which originate from mains-power lines.
Filtering time is inversely proportional to the frequency being filtered.
9. Tips and troubleshooting
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