SBC PCD2 Series User Manual

Saia-Burgess Controls AG
Manual I/O-modules for PCD1 │ PCD2 series │ Document 27-600 – Release ENG09 │ 2019-05-01
A-9
Appendix
Installation direction and relays contact protection
A
A.6.3 Switching inductive loads
Because of the physical properties of inductive loads, it is not possible to discon-
nect inductance without interference. This interference must be minimized as far
as possible. Although the Saia PCD
®
is immune to this interference, there are
other devices which may be susceptible.
It should be noted here that, as part of the harmonization of standards throughout
theEU,EMCstandardshaveappliedsince1996(EMCDirective89 / 336 / EG).
Twormprinciplescanthereforebestated:
●
PROTECTION AGAINST INTERFERENCE FROM INDUCTIVE LOADS IS
MANDATORY
●
INTERFERENCE SHOULD BE ELIMINATED AS CLOSE AS POSSIBLE TO ITS
SOURCE
Relay contacts on the present module have been wired. However, it is still recom-
mendedthataprotectioncircuitshouldbettedattheload.
(Often available as normal components on standardized contactors and valves).
When switching direct voltage it is urgently recommended that a recovery diode is
ttedabovetheload.Thisshouldeventakeplacewhen,theoretically,anOhmic
load is switched. In practice, there will always be a proportion which is inductive
(connection cable, resistance coil, etc.). In this case it should be noted that the
switch-o󰀨timewillbelonger.
(ApproximateTa.L / RL*√(RL*IL / 0,7).
For direct voltage, transistor output modules are recommended.
A.6.4 Relay manufacturer’s information on RC unit dimensioning
Wiring contact protection:
The purpose of contact protection wiring is to suppress switch arcing (“sparks”)
and thereby prolong the lifetime of the contacts. All protection wiring has disad-
vantages as well as advantages. For the cancellation of arcing by means of an RC
unit, see adjacent diagram.
Whenswitchingo󰀨loadcircuitswithinductivecomponents(e.g.relaycoilsand
magnet coils) the interruption of current results in overvoltage (standard induc-
tance) at the switching contacts. This may amount to many times the operating
voltage and so threaten the insulation of the load circuit. The resultant breaking
spark leads to rapid wear of the relay contacts. For this reason contact protection
wiring is particularly important with inductive load circuits. Values for the RC com-
bination can also be determined from the adjacent diagram. However, for voltage
U it is necessary to use the overvoltage arising from the interruption of current
(e.g. measurable with an oscillograph). Current must be calculated from this volt-
age and the known resistance, against which the voltage was measured.
Screening units should only use anti-interference capacitors that comply with VDE
0565 T1 class X2. These capacitors are switchproof and designed for particularly
high switching surges. They can also run directly on mains voltage.

SBC PCD2 Series Specifications

General

Brand	SBC
Model	PCD2 Series
Category	I/O Systems
Language	English