Meilhaus Electronic ME-5100 cPCI, Руководство пользователя, Страница: 26 / 43

The time reference is provided by a 66 MHz counter. It is config-
ured using the function. A period of 15.15 ns fol-
lows from this, and is defined as the smallest unit of time. It is re-
ferred to below as “1 tick”. The resolution for T and t
1P
is therefore
1 tick (see also the specifications on page 32).
Note that the value of the maximum period T
max
. depends on the
duty cycle. A distinction is drawn between rectangular signals with
an asymmetrical duty cycle T
max. asym
. and a symmetrical duty cycle
T
max. sym
. The figures for the ME-5100 are:
T
max. asym
. = 32.5 s (0.03 Hz); T
max. sym
. = 65 s (0.015 Hz)
The wiring of the frequency inputs/outputs can be found in chapter
3.5 on page 19.
4.1.2.1 Frequency Measurement
With the frequency measurement operating mode (FI=”Frequency
Input”) you can determine the period or frequency, and the duty cy-
cle of rectangular signals up to about 5.5 MHz. The resolution is 1
tick = 15.15 ns. The measurement always starts at a rising edge.
On the ME-5100, all 4 frequency measuring channels (FI_AO…3)
are addressed as subdevices of type ME_TYPE_FI, subtype
ME_SUBTYPE_SINGLE. Each channel can be programmed inde-
pendently.
Note: If the frequency and duty cycle are the magnitudes you want,
these can easily be calculated from the values returned for
<pdTime>.
The formula is:
Frequency [Hz] = 1/period [s]