FX Series Programmable Controllers Devices in Detail 4
4-27
Note: Bi-directional counters are desi
ned such that the up count si
nal and the down count
si
nal never operate at the same time. Therefore it is reall
usin
onl
one phase at one time.
Thus, the
can be treated in the same wa
as the 1 phase counters when calculatin
the
combined frequenc
.
Combined frequencies:
• The combined frequenc
is the sum of the maximum frequencies of all the si
nals
simultaneousl
appearin
at the inputs of the PLC. The criteria is that in order for the
hi
h speed counters to count correctl
the
must have a combined frequenc
of less
than 20 kHz.
Example:
The combined frequenc
of 14.2 kHz is lower than the maximum of 20 kHz, so this example is
valid.
A/B Phase counters:
When calculatin
a combined frequenc
which includes an A/B phase counter, the maximum
countin
frequenc
should be multiplied b
a factor of 4 before addin
the maximum
frequencies of the combinin
counters.
Example:
The combined frequenc
of 11 kHz is lower than the maximum of 20 kHz, so this example is
valid.
2 Phase counters:
• When pulses arrive at the up and down count inputs at the same time, treat this as 2
sin
le phase counters when calculatin
the combined frequenc
.
ClockWise - Counter-ClockWise format encoders:
• When encoders with CW and CCW format inputs are used, the bi-directional counters
can count at a much hi
her frequenc
than the A/B phase counters, there is also no loss
in resolution.
1 Phase counters Corresponding input Maximum signal frequency
C235 X0 4.2 kHz
C237 X2 4 kHz
C240 X3 6 kHz
Combined frequenc
14.2kHz
1 Phase counters Corresponding input Maximum signal frequency
1- Phase C237 X2 3 kHz
Bi-directional C246 X0, X1 4 kHz
A/B Phase C255 X3, X4 1 kHz
×
4
Combined frequenc
3 + 4 + (1
×
4) = 11kHz
