Electrical connections
Ex p Control unit
SILAS
pz
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A1-37S2-7D0001_pz_Manual_Exp-Control-Unit_20210923_0_en.docx
Rev. 0
Inductive loads
ATTENTION
INTERFERENCE FROM INDUCTIVE LOADS CAN DESTROY THE EXP CONTROL
UNIT.
Over voltages occur when switching off inductive loads (e.g. contactor coils).
Voltage peaks of up to 4 kV can occur with a voltage slope of 1 kV /
microsecond.
Interference suppression of AC-fed inductive loads by means of a
varistor.
Suppressing DC-fed inductive loads by means of a freewheeling
diode.
For inductive loads, use protective circuits to limit the voltage peaks that occur
during switch-off.
The consequences of this can be:
Coupling of interference signals that generate false signals
Destroy the Ex p control unit.
Protective circuits protect the Ex p control unit from premature failure due to the
overvoltage that occurs when the current flowing through an inductive load is
interrupted. In addition, protective circuits limit the electrical disturbances that
occur when switching inductive loads.
Protective circuit for AC supplied inductive loads
This circuit variant is used for inductive loads AC
voltage fed relays / contactors. In this circuit variant,
the property of the VDR resistor is exploited to
become low-resistance above a certain threshold
voltage. This short-circuits the self-induction voltage.
Any oscillation that arises is damped by the RC snubber.
Interference suppression measure, e.g. BARTEC 07-7311-93GU/K000
RC snubber
Varistor
Protective circuit for DC supplied inductive loads
This circuit variant is used for DC-powered relays /
contactors. A diode is connected in reverse direction
parallel to the coil.
Interference suppression measure, e.g. BARTEC 07-7311-61GF/5400
Free-wheeling diode
