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Period Duration Measurement Operating Mode
6.1
Function Description
Measuring range
Table 6-1
Measuring ranges
Counting
Lower
Range
Counting
Value
16 bits
100
6-2
In this operating mode, the CM35 uses period duration measurement to ac-
quire small frequencies.
The CM35 measures the exact time between two falling edges of the count-
ing signal by counting the pulses of an internal precision-quartz reference
frequency. The period duration of the input signal is calculated from the
counting value after a period, divided by the reference frequency (in kHz).
Example:
- - Counting value = 100
- - Reference frequency = 100 kHz (standard value)
100
= 1 msec ( 1 kHz)
100 kHz
Þ Period duration = 1 msec or frequency = 1 kHz
At a measuring value width of 16 bits and a reference frequency of 100 kHz,
period duration measurements between 655 msec (counting value 65500) and
1 msec (counting value 100) can be performed with a resolution of 1% with-
out switching the range.
Note
The resolution depends on the lower counting value (i.e., the minimum
period duration).
The reference frequency can be adjusted for measurement of longer period
durations. The following table shows the reference frequencies and the result-
ing measuring range.
Upper
Reference Frequency
Counting
Value
65500
100 kHz
50 kHz
25 kHz
Measuring Range
655 msec to 1 msec
(1.53 Hz to 1 kHz)
1,310 msec to 2 msec
(0.76 Hz to 500 Hz)
2,620 msec to 4 msec
(0.38 Hz to 250 Hz)
CM35 Counter Module
(4) J31069-D0416-U001-A5-7618
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