schmersal PROTECT-PSC - Page 68

System description
3
Instruction Manual PROTECT-PSC
V 2.6R01 / 04.19
3–36
3.7.5 Voltage monitoring
Monitoring under-voltage and over-voltage
The voltage watchdog ensures a controlled power shut-down in the case of error in
the power supply. Drops in power of up to 10 ms are buffered by a buffer circuit.
The state of the internal voltage is displayed by means of the PWR LED.
1. Correct switching-on/switching-off of the supply voltage
24V
0V
PWR - LED
External voltage
Internal voltage
on
off
on
off
F
F
i
i
g
g
u
u
r
r
e
e
3
3
-
-
1
1
5
5
C
C
o
o
r
r
r
r
e
e
c
c
t
t
s
s
w
w
i
i
t
t
c
c
h
h
i
i
n
n
g
g
-
-
o
o
n
n
/
/
s
s
w
w
i
i
t
t
c
c
h
h
i
i
n
n
g
g
-
-
o
o
f
f
f
f
o
o
f
f
t
t
h
h
e
e
s
s
u
u
p
p
p
p
l
l
y
y
v
v
o
o
l
l
t
t
a
a
g
g
e
e
After applying the supply voltage the internal 3.3 volt supply is switched on and the
PWR LED lights up. If the external supply is switched off, a controlled Power Down
is performed and the PWR LED goes out.
2. Brief drop in voltage (≤ 10 ms)
24V
0V
PWR - LED
External voltage
Internal voltage
on
off
on
off
F
F
i
i
g
g
u
u
r
r
e
e
3
3
-
-
1
1
6
6
B
B
r
r
i
i
e
e
f
f
d
d
r
r
o
o
p
p
i
i
n
n
v
v
o
o
l
l
t
t
a
a
g
g
e
e
(
(
≤
≤
1
1
0
0
m
m
s
s
)
)
A brief drop in voltage (up to 10 ms) is buffered by the internal buffer circuit and
has no influence on the operation of the PROTECT-PSC.
3. Drop in voltage (> 10 ms)
24V
0V
PWR - LED
External voltage
Internal voltage
PWR - LED
on
off
on
off
F
F
i
i
g
g
u
u
r
r
e
e
3
3
-
-
1
1
7
7
D
D
r
r
o
o
p
p
i
i
n
n
v
v
o
o
l
l
t
t
a
a
g
g
e
e
(
(
>
>
1
1
0
0
m
m
s
s
)
)
In the case of a drop in voltage > 10 ms the internal Power Down measure is initi-
ated. The PWR LED goes out. In addition the special Flag VC1 is set. Drops in
voltage > 1s are recognised as shut-down and the special Flag VC1 is not set.