IB IL 24/230 DOR 4/W-PC (-PAC)
8
6530B
Interference Suppression Measures
on Inductive Loads/Switching Relay
Each electrical load is a mixture of ohmic, capacitive,
and inductive elements. Depending on the proportion
of the element, switching these loads results in a
larger or smaller load on the switch contact.
In practice, loads are generally used with a large
inductive element, such as contacts, solenoid valves,
motors, etc. Due to the energy stored in the coils,
voltage peaks of up to several thousand volts may
occur when the system is switched off.
These high voltages cause an arc, which may destroy
the controlling contact through material evaporation
and material transfer.
This pulse, which is similar to a square wave pulse,
emits electromagnetic pulses over a wide frequency
range with a large amount of power and with spectral
elements reaching several MHz.
To prevent such arcs from occurring it is necessary to
fit the contacts/loads with protective circuits. The
following protective circuits can be used:
–
Contact protective circuit
–
Load protective circuit
–
Combination of both protective circuits
Figure 8
Contact protective circuit (A), load
protective circuit (B)
If sized correctly, these circuit versions do not differ
greatly in their effectiveness. In principle, a protective
measure should be directly implemented at the
source of the interference. In addition, the following
points should be observed for a load protective circuit:
–
When the contact is open, the load is electrically
isolated from the operating voltage.
–
It is not possible for the load to be activated or to
"stick" due to undesired operating currents,
e.g., from RC elements.
–
Shutdown voltage peaks cannot be coupled in
control lines that run in parallel.
Phoenix Contact provides protective circuit solutions
in terminal format or in electronic housing (see the
"CLIPLINE" catalog or "TRABTECH" catalog).
Additional information is available on request. In
addition to this, today the majority of contact
manufacturers offer diode, RC or varistor elements
that can be snapped on. For solenoid valves,
connectors with an integrated protective circuit can be
used.
A
B
5 9 7 3 A 0 2 8
