gefran ILI Series Original Operating Instructions page 35

Generally, a concave formation appears on the cathode and a convex formation appears on the anode.
Contact protection circuit
Use of contact protective devices or protection circuits can suppress the counter emf to a low level.
However, note that incorrect use will result in an adverse effect.
Typical contact protection circuits are given in the table below.
Contact protection circuit: Inductive load
Circuit
CR
circuit
Diode
circuit
Diode
and
zener
circuit
Varistor
circuit
(G: Good, NG: No Good, C: Care)
Mounting the protective device
80618_MAN_IO-LINK IMPACT_12-2019_ENG
Figure 11
Voltage
Features/Others
CA CD
If the load is a timer, leakage
current flows through the CR
circuit causing faulty operation.
C* G * If used with AC voltage, be
sure the impedance of the load
is sufficiently smaller than that
of the CR circuit
If the load is a relay or
solenoid, the release time
G C lengthens.
Effective if the power supply
voltage is 24 or 48V.
The diode connected in
parallel causes the energy
stored in the coil to flow to the
coil in the form of current and
dissipates it as joule heat at the
resistance component of the
NG G
inductive load.
This circuit further delays the
release time compared to the
CR circuit.
(2 to 5 times the release time
listed in the catalog)
Effective when the release time
NG G
in the diode circuit is too long.
Using the stable voltage
characteristics of the varistor,
this circuit prevents excessively
G G high voltages from being
applied across the contacts.
This circuit also slightly delays
the release time.
Devices Selection
As a guide in selecting "c" and "r",
c : 0.5 μF to 1μF for 1A contact current
r : 0.5 Ω to 1 Ω per 1V contact voltage
Values vary depending on the properties of the
load and variations in relay characteristics.
Capacitor "c" acts to suppress the discharge the
moment the contacts open.
Resistor "r" acts to limit the current when the
power is turned on the next time.
Use a capacitor "c" with a breakdown voltage of
200 to 300V.
Use AC type capacitors (non polarized) for AC
circuits.
Use a diode with a reverse breakdown voltage at
least 10 times the circuit voltage and a forward
current at least as large as the load current.
In electronic circuits where the circuit voltages
are not so high, a diode can be used with a
reverse breakdown voltage of about 2 to 3 times
the power supply voltage.
Use a zener diode with a zener voltage about
the same as the power supply voltage.
-
35