User Manual

CE1N5365E / 05.11.1998 Siemens Building Technologies
2/4 Landis & Staefa Division
The M-bus signal converter is for connection between the M-bus central unit and an M-
bus segment (bus section with M-bus devices).
As a
signal converter
, the WZC-P250 converts the RS-485 signals to M-bus signals.
For this purpose, the converter is equipped with an RS-485 interface card. It has LEDs
to indicate the direction and type of the current flow of data.
LED Status Data flow
LED 1 (red) On Master sending
Off Master in idle state
LED 2 (yellow) On Slave sending
Off Slave in idle state
As a
bus driver
, the M-bus signal converter delivers the quiescent current to a
maximum of 250 M-bus devices. According to standards, the maximum current drawn
by an M-bus user is 1.5 mA, representing one "M-bus load". The M-bus output (typically
DC 40 V) is protected against short-circuits.
The interface between the M-bus central unit and the M-bus signal converter is
galvanically separated by an optocoupler:
Power is delivered by a power pack (DC 42 V). On the M-bus signal converter, the
direction and type of current data flow are indicated by LEDs:
LED Designation Status Data flow
LED 1 (green) “ON” On Bus voltage present, master in idle
state
Flashing Bus voltage present, master sending
LED 2 (yellow) “SLAVE” On Slave sending
Off Slave in idle state
LED 3 (yellow) “MAX” On Normal bus current exceeded
LED 4 (red) “SHORT” Flashing at 2 Hz Overcurrent
The M-bus signal converter consists of casing and detachable mounting base. The
casing is designed for wall mounting.
When closed, no indication or setting elements are visible. When opening the bottom
section of the casing, the connection terminals and LEDs can be accessed.
The terminal blocks carry two rows of contacts. The top row is used for the positive
potentials while the bottom row is used for the negative potentials.
The RS-485 interface card is an extra plug-in card. The card and its LEDs can be
accessed after removing the unit cover.
The local regulations on electrical installations must be complied with.
For the design of M-bus systems, please refer to the Planning Handbook, J5361.
Connect the DC 42 V power pack to the terminals 42 V + and - and to the earth terminal
E.
It must be made absolutely certain that the polarity of the power pack will be
correct!
Before making the connections, it is recommended to check the polarity with a
multimeter.
Technical design
Mechanical design
Engineering notes
Fitting notes