Tohnichi R-BL, Operation Manual

Page: 15 / 28

13
f Contact Protection Circuit
When the inductive load is opened or closed, a counter-electromotive voltage is generated
and causes a heavy damage to the contact, resulting in a significant shortening of operating
life. Therefore, a contact protection circuit is required. The examples of contact protection
circuits are as shown in the table below.
AC DC
If this circuit is used for timer
loads, leakage current flowing
through cr cause faulty operation.
*If used with AC voltage,
impedance of the load should be
○ ○
D
i
o
d
e
t
y
p
e
×
○
Energy stored in the coil is
discharged to the coil by flow of
current by the diode connected in
parallel to the load and is
consumed by joule heat of the
resistance of the inductive
Use a diode with a peak inverse
voltage 10 times higher than the
circuit voltage and a forward current
as high as or higher than the load
current. In an electronic circuit
where the circuit voltage is not so
high, a diode with a peak inverse
voltage about 2 to 3 times higher
Selection of element Circuit example
C
R
t
y
p
e
※
△
○
The standard c and r are as follows:
c
：
0.5 to 1 (μF) per contact current
(1A)
r
：
0.5 to 1(Ω) per contact vaolage
(1V)
The above values vary depending on
the property of load or variations in
relay characteristic. Considering that
the capacitor "c" has the effect of
controlling the discharge when the
contactes are open and the resistor
"r" plays the role fo controlling the
current at the next power-on, check
through experiments is required.
Normally, use a capacitor with a
If the load is a relay or solenoid, the
reset time is delayed. It is effective
to connect between the loads when
the power supply voltage is 24 or
48V and to connect between the
contacts when the power supply
voltage is 100 to 200V
Applicability
Features/others
r c
Relay contact
I n
d u
c
t i v
e
l o
a d
r
c
Relay contact
I n
d
u
c
t i v
e
l o
a
d
Relay contact
Diode
I n
d
u
c t i
v e
l o
a
d