PR821-CH User Manual.doc
2018-04-05
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3.3 Power supply
Controllers require 12VDC nominal power supply. The power must be connected to +12V and -12V
terminals. Additionally, the -12V line can be used as reference potential for the RS485 bus, IN1-IN3
input lines and RACS CLK/DTA bus. The power supply can be provided by means of power supply
unit (e.g. PS-15DR, PS20) which can be equipped with backup battery in order to ensure operation
of access control in case of power failure.
Note: All devices connected to RS485 bus (including controllers) should have the same supply
minus (GND). In order to ensure this, all the GND terminals from various power supply units within
the system should be connected with each other using separate wire. Alternatively, the common
supply minus of the entire system can be earthed however only in one point.
3.4 Connection of door lock
In majority of cases, door locking devices are inductive type. It means that overvoltage (voltage
surge) can occur when current flow is interrupted and it can interfere with the controller electronic
components. In extreme cases it may result in improper operation of the controller or even freeze.
Moreover, overvoltage condition causes quicker wear of relay contacts. In order to limit this
negative effects, it is necessary to use a general type semiconductor diode e.g. 1N4007 (one piece
of such diode is included with the controller). It should be connected as close as possible to the
inductive element (electric strike or magnetic lock).
Fig. 3 Connection of door lock
3.5 Communication with controller
RS485 bus and UT communication interface (e.g. UT-2USB) are used for communication with
controller. Single RS485 bus creates network (subsystem) and up to 32 controllers with unique
addresses in range of 00..99 can be connected to the bus. For the communication with distant
subsystems it is required to use UT-4DR or UT-4 v2.0 communication interface or CPR32-NET
network controller as all of them enable communication through computer network (LAN or WAN).
The RS485 bus consists of two signal lines A and B. In the RACS 4 system any topology can be
used (star, tree or any combination of them, except for loop) in order to connect controllers in
network (subsystem). The matching resistors (terminators) connected at the ends of transmitting
lines are not required. In most cases communication works with any cable type (standard telephone
cable, shielded or unshielded twisted pair etc.) but the recommended cable is unshielded twisted
pair (U/UTP cat.5). Shielded cables should be limited to installations subject to strong
electromagnetic interferences. The RS485 communication standard used in the RACS 4 system
