Kipp&Zonen COMBILOG Data Logger - Manual (Page 48)

5.2.2 Frequency Measurement
With frequency measurements the data logger counts the pul-
ses within a certain time interval at the digital input. The user
can preset this time interval by setting the time base (TB) in the
range between 0.1 sec and 10 sec. The frequency is calculated
by the sensor module from the number of pulses and the time
base TB as:
frequency f =
number of impulses per time interval TB
length of time intervall TB
Hz
With frequency measurements always the negative signal edge
(1
-
> 0) is counted.
The lower the frequency f, the larger the interval between two
pulses, and the larger the time base TB has to be. On the other
hand the updating of the measured value decreases with an in-
creasing time base. Thus the time base should be selected so
as to make TB
≈ 1/f
u
, f
u
being the lowest frequency respectively
the smallest change in frequency to be determined by the data
logger. The error with frequency measurements thus amounts
to
∆ f = f
u
= 1/TB.
Note: The high-end frequency for the frequency measurement,
i.e. the highest frequency to be measured. It is 4000 Hz.
Hardware Manual COMBILOG 1022 48