App-19
IM DL850E-01EN
Appendix
Appendix 5 Measurement Principle of the Frequency Module
Measurement Principle (Measurement Method and Update Rate) of the Frequency
Module
The measurement principle of the period, frequency, pulse width, and duty cycle on the frequency module (701280
(FREQ)) is described below.
Period and Frequency Measurement
The frequency module updates the waveform at a rate of 25 kHz (40 μs interval). The measurement method
differs for frequencies above 25 kHz and below 25 kHz as described below.
• When the input signal is less than or equal to 25 kHz, measurement is made as described in (1).
• When the input signal is greater than or equal to 25 kHz, measurement is made as described in (2).
• The sequence of processing described below is performed simultaneously through pipeline processing. Thus,
the period (t) and frequency (f) are updated every 40 μs.
(1) When the input signal is less than or equal to 25 kHz
The module measures the time of occurrence of the pulse edge (T1) in measurement interval A.
The module measures the time of occurrence of the pulse edge (T2) in measurement interval B.
The module calculates the period (t) in measurement interval C. t = T2 − T1
The frequency (f) is calculated as 1/period (t).
When the period of the input pulse spans over multiple measurement intervals, computation is performed in
the measurement interval following the interval in which the edge is detected.
Input pulse
Measurement
interval: 40 μs
Time: T1
Time: T2
A
B
Period (t)
Period (t) = T2 – T1
Frequency (f) = 1/period (t)
40 μs
C
40 μs
(2) When the input signal is greater than or equal to 25 kHz
The module measures the time of occurrence of the last pulse edge (Te1) in measurement interval A.
The module measures the time of occurrence of the last pulse edge (Te2) in measurement interval B.
The module measures the number of pulses between the last pulse edge in measurement interval A and the
last pulse edge in measurement interval B.
The module calculates the period (t) in measurement interval C. t = Te2 − Te1/number of pulses
The period (t) calculated is the average value of multiple pulses.
The frequency (f) is calculated as 1/period (t).
If the input pulse period is short, the DL850E/DL850EV automatically takes the average of multiple pulses and
calculates the period and frequency. Therefore, the resolution does not degrade even when the input pulse
period is short, and highly accurate measurement is possible.
Time: Te1
Input pulse
Period (t) = (Te2 – Te1)/3
Frequency (f) = 1/period (t)
Measurement
interval: 40 μs
Number of pulses: 3
Time: Te2
A
B
C
40 μs
40 μs