Fig. 21 Switch-Off Of Inductive Loads - Beckhoff EL2124 Documentation

Short-circuit or prolonged overload on a channel leads to an increase in the device temperature. If several
channels are overloaded, this leads to a rapid increase in the device temperature. The overloaded channels
are switched off when the upper limit for the device temperature is exceeded. The channels are only
switched on again if the temperature falls below the lower limit values for both the device and the channel.
The non-overloaded channels continue operating properly.
When switching off inductive loads, high induction voltages result from interrupting the current too quickly.
These are limited by an integrated free-wheeling diode (breaking energy see Technical data). Since the
current reduces only slowly, a delayed switch-off can occur in many control applications. For example, a
valve remains open for many milliseconds. Switch-off times are realized that correspond, for instance, to the
switch-on time of the coil.
Protection against high induction voltages
To protect against voltage peaks such as can occur when switching inductive loads, we recommend
to provide suitable protective circuits (e.g. with the free-wheeling diode, RC combination or varistor)
directly at the actuator.
Fig. 21: Switch-off of inductive loads
EL20xx, EL2124
Product overview, digital output terminals
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