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The BL20 Solution

TURCK 7/20/2018

The BL20 modular concept is a very flexible approach to terminal-wired I/O. The gateway, base and electronic modules provide many benefits to the user.

• The gateway provides communication between the fieldbus and I/O modules; modules are not dependent on the fieldbus protocol.
• DIN-rail mountable base modules are available with different wiring configurations to suit the user’s needs.
• Electronic modules are hot swappable.
• Power distribution modules can be used to create isolated power segments within the system.

BL20’s openness and flexibility provide a viable alternative to traditional PLC I/O.

Maximum Size of a BL20 Station

BL20 stations consist of a gateway and a maximum of 74 I/O modules (equivalent to 1 m station length). Some high-tech and analog I/O modules may consume or produce large amounts of data, and therefore may further limit the number of modules that may be used. It is highly recommended that I/Oassistant software is used when planning and commissioning BL20 systems. This program allows you to build the BL20 node on your computer and verify that all restrictions with regard to power and size are met. The free I/Oassistant software is available to download from TURCK website.


As a node on a network, the BL20 station must have an address. The setting of this address is dependent on the network system being used. Each network gateway has a set of rotary switches (one for the most significant digit, or 10’s multiplier, and one for the least significant digit, or 1’s multiplier) that are used to set the address for the node. DeviceNet™ gateways may be addressed between 0 and 63, while PROFIBUS®-DP and CANopen gateways can be set from 0 to 99.

BL20 Power Distribution

The power supply for a BL20 station is fed via power feeding or bus refreshing modules; the latter also being responsible for the power supply to the internal module bus. Bus refreshing modules are used within a BL20 station (without gateway supply) if the system supply to the BL20 modules (nominal current IMB 1.5 A) is no longer sufficiently guaranteed. Bus refreshing modules are used with tension clamp (BL20-P3T-SBB-B or BL20-P4T-SBBC-B) or screw connection base modules (BL20-P3S-SBB-B or BL20-P4S-SBBC-B). Power feeding modules are used if the system supply to the BL20 modules (nominal current IL < 10 A) is no longer sufficiently guaranteed.

System Supply Via Module Bus

The amount of BL20 modules that may be supplied by a bus refreshing module via the internal module bus depends on the respective minimal current IMB of the individual modules on the bus. The sum of the nominal current inputs of the connected BL20 modules must not exceed 1.5 A. BL20 gateway power requirements (supplied by the first bus refreshing module) should be considered when calculating the required number of bus refreshing modules. If I/Oassistant software is used, an error message is generated automatically via the as soon as the system supply is no longer sufficiently guaranteed.

All bus refreshing modules used in a BL20 station should be connected via the same frame potential. The power supply to the bus is fed via the connections 11 (plus) and 21 (ground) of the respective base module for the bus refreshing module.

Creating Potential Groups

Both bus refreshing modules and power feeding modules may be used to create a potential group. The base module creates the possible isolation of the potential group on the left-hand side of the respective power distribution module.

It is not permitted for modules with 24 VDC and with 120/230 VAC field supply to be used in a joint potential group. Therefore, when using digital input modules for 120/230 VAC, the power feeding module BL20-PF-120/230VAC-D is to be used to create a special potential group.

C-rail (Cross Connection)

C-rails run through all I/O base modules. The C-rail for base modules for power distribution is mechanically separated; thus potentially isolating the adjoining supply groups.

Access to the C-rail

Access to the C-rail is made via base modules with a C designation (i.e. BL20-S4T-SBCS). The corresponding connection level is indicated by a thick black line on all base modules for BL20 I/O modules. For base modules for power distribution, the black line is only above the connection “24" to indicate that the C-rail is separated from the adjoining potential group to its left.

It is permitted to load the C-rail with a maximum of 24 V; never with 120/230 VAC.

Using the C-rail with Relay Modules

The C-rail may be used to supply a common voltage when relay modules are used. To accomplish this, the load voltage (24
VDC) is connected to a power distribution module and the base module BL20-P4x-SBBC with either tension clamp or screw connections.

If the C-rail is used for the joint supply of voltage to relay modules, there must be a power distribution module used for the potential isolation of the BL20 modules. The C-rail may still be used as protective earth (PE) once the potential isolation has been made.

Using the C-rail as a Protective Earth

A C-rail may be used as a protective earth (PE), where the PE connection for each power distribution modules must be connected to the mounting rail via an additional PE terminal, which is available as an accessory.