Description of the individual safety relays
3.8 3TK28 safety relays with contactor relay enabling circuits
3TK28 safety relays
Manual, 07/2016, NEB926157502000/RS-AB/003
171
3.8.4
3TK2856 / 3TK2857 safety relays
3.8.4.1
Applications
Applications of 3TK2856/57 expansion units
You can use the 3TK2856/57 expansion units in conjunction with all 3TK28/3RA7 basic
units. It is used to expand the enabling circuits.
The maximum achievable performance level PL / Cat. in accordance with
DIN EN ISO 13849-1, or SILCL in accordance with IEC 62061 is equivalent to the PL / Cat. /
SILCL of the basic unit if the external circuitry (connection between basic unit and expansion
unit) is failsafe.
3.8.4.2
Description of function and connection information
The 3TK2856/57 expansion units have two contactor relays as switching elements, one safe
solid-state output, one safe input for cascading and one input for functional switching.
The operating state and functioning are indicated by three LEDs.
On startup, the device runs a self-test in which the internal electronics are checked for
correct functioning.
All internal parts of the circuit are cyclically monitored for faults during operation.
With safe output 2, additional expansion units, such as 3TK2830/56/57 and external
actuators or loads, can be switched.
Also, cascading with units 3TK2841/42/45/53 is possible via safe output 2. In the case of
PL
d/e
or SILCL 2/3, single-channel cascading is only possible within one cabinet.
Make sure that the actuator/load and the 3TK2856/57 expansion unit have the same ground
potential.
OFF-delay times
The table below provides an overview of the OFF-delay times t
v
.
Table 3- 6
3TK2856
Rated control supply voltage
U
S
[V]
Start type
OFF delay t
V
[s]
Article No.
Screw-type
Article No.
Spring-loaded
24 V DC
-
-
3TK2856-1BB40
3TK2856-2BB40
Table 3- 7
3TK2857
Rated control supply voltage
U
S
[V]
Start type
OFF delay t
V
[s]
Article No.
Screw-type
Article No.
Spring-loaded
24 V DC
-
0,05 ... 3
3TK2857-1BB41
3TK2857-2BB41
0,05 ... 30
3TK2857-1BB42
3TK2857-2BB42
5 ... 300
3TK2857-1BB44
3TK2857-2BB44