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xxxi
Conformance to EC Directives
6
Countermeasures
Countermeasures are not required if the frequency of load switching for the
whole system with the PLC included is less than 5 times per minute.
Countermeasures are required if the frequency of load switching for the whole
system with the PLC included is more than 5 times per minute.
Note
Refer to EN61131-2 for more details.
Countermeasure Examples
When switching an inductive load, connect an surge protector, diodes, etc., in
parallel with the load or contact as shown below.
Circuit
Current
Characteristic
Required element
AC
DC
Yes
Yes
If the load is a relay or solenoid, there is
a time lag between the moment the cir-
cuit is opened and the moment the load
is reset.
If the supply voltage is 24 or 48 V, insert
the surge protector in parallel with the
load. If the supply voltage is 100 to
200 V, insert the surge protector
between the contacts.
The capacitance of the capacitor must
be 1 to 0.5
µ
F per contact current of
1 A and resistance of the resistor must
be 0.5 to 1
Ω
per contact voltage of 1 V.
These values, however, vary with the
load and the characteristics of the
relay. Decide these values from experi-
ments, and take into consideration that
the capacitance suppresses spark dis-
charge when the contacts are sepa-
rated and the resistance limits the
current that flows into the load when
the circuit is closed again.
The dielectric strength of the capacitor
must be 200 to 300 V. If the circuit is an
AC circuit, use a capacitor with no
polarity.
No
Yes
The diode connected in parallel with
the load changes energy accumulated
by the coil into a current, which then
flows into the coil so that the current will
be converted into Joule heat by the
resistance of the inductive load.
This time lag, between the moment the
circuit is opened and the moment the
load is reset, caused by this method is
longer than that caused by the CR
method.
The reversed dielectric strength value
of the diode must be at least 10 times
as large as the circuit voltage value.
The forward current of the diode must
be the same as or larger than the load
current.
The reversed dielectric strength value
of the diode may be two to three times
larger than the supply voltage if the
surge protector is applied to electronic
circuits with low circuit voltages.
Yes
Yes
The varistor method prevents the impo-
sition of high voltage between the con-
tacts by using the constant voltage
characteristic of the varistor. There is
time lag between the moment the cir-
cuit is opened and the moment the load
is reset.
If the supply voltage is 24 or 48 V, insert
the varistor in parallel with the load. If
the supply voltage is 100 to 200 V,
insert the varistor between the con-
tacts.
---
CR method
Power
supply
Inductiv
e
load
C
R
Diode method
Power
supply
Inductiv
e
load
Varistor method
Power
supply
Inductiv
e
load
Содержание CP1L-L14D Series
Страница 2: ...CP1L L14D CP1L L20D CP1L M30D CP1L M40D CP1L CPU Unit Operation Manual Revised June 2007...
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Страница 13: ...xiv TABLE OF CONTENTS...
Страница 21: ...xxii...
Страница 33: ...xxxiv Conformance to EC Directives 6...
Страница 65: ...32 Function Blocks Section 1 5...
Страница 153: ...120 CP CPM1A series Expansion I O Unit Wiring Section 3 6...
Страница 523: ...490 Troubleshooting Unit Errors Section 9 4...
Страница 531: ...498 Replacing User serviceable Parts Section 10 2...
Страница 563: ...530 Auxiliary Area Allocations by Function Appendix C...
Страница 611: ...578 Auxiliary Area Allocations by Address Appendix D...
Страница 638: ...605 Connections to Serial Communications Option Boards Appendix F Connecting to Unit...
Страница 639: ...606 Connections to Serial Communications Option Boards Appendix F...
Страница 669: ...636 Index...
Страница 671: ...638 Revision History...