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2TLC172001M0211_A
4.4.3 Sensor output types
Incremental encoders with HTL output and other with push-pull output can be used at
frequencies up to around 14 kHz. For sensors with “open collector”, “PNP” output, or other
output
not
of “push-pull” type the maximum frequency might typically be 1 – 4 kHz, but the limit
is dependent on the output resistance, the cable length etc.
The reason for this is that the signal will not have time to return to zero at higher frequencies.
This will be interpreted by Pluto and the function block as Speed=0.
4.4.4 “No Filt” settings for counters
For incremental encoders with HTL output and frequencies over 4 kHz the setting “No Filt” shall
be selected.
For lower frequencies and use of for example standard proximity switches the option “No Filt”
shall
not
be selected since the filter will give protection against disturbances.
4.4.5 Speed monitoring with two sensors
Overspeed, Safe low speed etc.
With a two-channel solution where 2 sensors monitor that the speed are within certain limits the
application can reach Category 3/PL d or 4/PL e if diverse types of sensors are used.
As long as there is a speed the two sensors can be compared with each other and if one fails it
is detected since they need to be equal.
Stand still monitoring, dual channel
For stand still monitoring with two sensors Category 3/PL d can be achieved. This requires
however that motion is detected regularly so that the application is tested. A typical solution is
every time a motion in a machine is started the PLC program requires a corresponding reaction
from the sensors / speed sources.
Note that in machines vibrations can cause indication of small speed values.
10V
0
1
1
0
10V
0V
+24V
Output
Sensor output
Signal at low frequency
Signal at too high frequency
(Pluto reads 0 speed.)
Signal behaviour for sensor outputs with no active pull to 0V.
0V
+24V
+24V
0V
Push-pull / HTL sensor output.
Open collector / PNP sensor output
Typical for incremental encoders
Typical for proximity sensors and photocells
