BECKHOFF FM33xx - Manual (Page 15)

Functional description
10 FM33xx
PE connection
The screening braids on the PROFIBUS cables are to be earthed at the
modules, in accordance with the PROFIBUS specification. This
requirement is satisfied by a low-resistance connection between the PE
connection to the ground of the local environment (the machine). The PE
connection is also responsible for the potential equalization of grounded
and non-grounded thermocouples, and for thermocouples grounded at
different potentials (see thermocouple measurement). The back voltage
protection diverts mains voltages via the PE connection. This means that it
is essential for proper earthing of the module to be guaranteed. When the
module is being fitted, the PE connection should be established first.
Connection of the module to the thermocouples via the connecting strip
should be performed subsequently. In this way the risk of back voltage
being present at the thermocouple inputs during assembly is avoided. If the
earthing is inadequate the user is exposed to hazardous voltages on the
housing. When the module is being dismantled, the module should, for this
reason, first be disconnected from the thermocouples before the PE
connection is removed.
Connecting strip for thermocouples
The thermocouples are connected to the 24-pin or 64-pin connection strips.
The signal assignment and polarity must be correctly observed. Cold
junction compensation is implemented on the circuit board within the
module. The connection between the module electronics and the connector
pins is made with the corresponding thermal material. The use of
thermocouples other than those listed in the documentation is not
permitted. Good thermal conduction between the module's plug and socket
means that no significant thermal voltage is created by the plugged
connections. Thermal insulation on the socket side of the connection
should be ensured in order to avoid a large temperature error. Draughts
and unevenly heated areas in particular are to be avoided.
Configuration interface
Serial interface under the
screwed cover The module has an RS232 interface at the top of the front panel under the
PG threaded fitting. The miniature connector can be linked through a
special cable to the serial interface of a PC. The module can be configured
with the KS2000 configuration software. The interface allows the analog
channels to be configured.
Switches for the station address
Two rotary switches are used to set the station address. The rotary
switches are located under the screwed cover next to the serial
configuration interface. The address is set as decimal number. The right-
hand rotary switch is for the units, and the left-hand switch sets the tens.
(Example: station address 18: left hand switch = 1, right hand switch = 8).
In order for a new station address that has been set to be permanently
stored in the module it must be reset (either by a brief interruption of the
power supply or by means of a software reset).