Hioki MEMORY HiCORDER 8855, Instruction Manual

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APPENDIX 6
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Appendix 3 Reference
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Appendix 3.1 Sampling
Sampling period
Measurement point
Time
Appendix 3.2 Aliasing
Sampling period
Actual input signa
Observed waveform
Aliasing occurs because sampling period
is longer than input signal period.
Appendix 3 Reference
The 8855 converts the input signal to a digital value, then carries out all
internal processing digitally. This process of converting an analog signal to
digital values is termed sampling.
Sampling measures the magnitude of the signal at fixed time intervals
(sampling periods).
The rate of taking these measurements is termed the sampling rate.
The units are S/s, read as samples per second.
This is the reciprocal of the sampling period (1/T).
If the frequency of the signal being measured is significantly higher than the
sampling rate, it is possible for sampling to produce an apparent signal
which is actually nonexistent. This phenomenon is termed aliasing.
When using the memory function, because the sampling period for the time
axis range may vary widely, care should be taken in setting the range not to
produce aliasing.
The measurement frequency limit is determined by the setting of the time
axis range. In any event, it is always best to use the highest practicable
sampling rate.
When measuring a repeating signal, using the auto ranging function is
another useful technique.