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OR and AND achievedwith (3/2-way) directional control valves
Logic function AND
The
AND
function presupposes the presence of the information (i.e independent signals) “
a
” and “
b
” at its two
inlets to generate the output signal
X
. Two 3/2-way valves connected in a suitable manner can also achieve the
same logic function.
Figure 46
Two valves, the first with its inlet connected to the compressed air network, the 2
nd
fed from the outlet of the first.
The two valves are connected in series, bothare3/2-way
NC
andonly if operated simultaneously, do they generate
their respective signals “
a
” and “
b
” with the consequent result
X
.
Logic equationwith the AND function:
a * b= X
Logic equationwith distribution valves:
a * b= X
1
2
3
a
b
a
b
a * b
b
a
X
X
a * b
a * b
a+b
a+b
a
Fig. 45
a
b
a
b
a * b =X
a * b =X
Fig. 46
Logic functionOR
The
OR
function presupposes the presence of at least one of the two independent signals “
a
” or “
b
” at its two
inlets to generate the output signal
X
. Two 3/2-way valves, connected in a suitablemanner can achieve the same
logic function.
Note
:whenusing the
NOT
functionas a limit switch, it is important to consider that output
X
is present in theevent
of an external mechanical stop of the piston rod/ piston before the end of the stroke. In addition, any adjustments
to the velocity are to be made on the exhaust of the 5/2-way valve. With flow regulators placed on the cylinder
ports, the pressure in the tube between themain valve and flow regulation valve is quickly reduced andmay not
be sufficient tomaintain the
NOT
piloted, whichwould activate the output
X
.
In this casewewould have a false reading, as the cylinder would still bemoving and not at the end position.
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