Kippzonen COMBILOG Data Logger Manuel d'utilisateur télécharger pdf (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

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

, f

being the lowest frequency respectively

the smallest change in frequency to be determined by the data

logger. The error with frequency measurements thus amounts

∆

f = f

= 1/TB.

Note: The high-end frequency for the frequency measurement,

i.e. the highest frequency to be measured. It is 4000 Hz.

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Kippzonen COMBILOG Data Logger Manuel d'utilisateur Page 48