EUCHNER CETx-AR-xxx-AH-xxx (Unicode) - Manual (Page 21)

Operating Instructions Safety Switch CET.-AR-...-AH-...
21
Determining cable lengths using the example table
Example: 6 switches are to be used in series. Cabling with a length of 40 m is
routed from a safety relay in the control cabinet to the last switch (#6). Cables
with a length of 20 m each are connected between the individual CES-AR/CET-AR
safety switches.
Fig. 3: Circuit example with six CES-AR/CET-AR
A safety relay is connected downstream which consumes 75 mA at each of the
two safety inputs. This operates over the whole temperature range with a voltage
of 19.2 V (corresponds to 24 V -20%).
All the relevant values can now be determined using the example table:
1. Select the corresponding section in the column n (max. number of switches).
Here: 6 switches.
2. In column I
OA/OB
(possible output current per channel OA/OB), find a current
greater than or equal to 75 mA. Here: 100 mA.
¨ It is then possible to determine the maximum cable length from the last switch
(#6) to the control system from column l
1
. Here: a length of 50 m is permitted.
Result: The desired cable length l
1
of 40 m is below the permitted value from the
table. The overall length of the switch chain l
max
of 140 m is less than the maximum
value of 200 m.
¨ The planned application is therefore functional in this form.
CET-AR # 6
Sicherheits-
relais
Safety Relay
CES-AR # 5 CES-AR # 3 CES-AR # 2 CES-AR # 1
CET-AR # 4
l
1
= 40 m l
2
= 5 x 20 m
l
max
= 140 m
l
n
= 20 m
u
n
= min. 19,2 V
i
OA/OB
= min. 75 mA