User manual

Berghof Automationstechnik Analog I/O expansion module
2VF100051FE01.doc 2D0172002ZD00.DOC 21
2.8.2. Sensor connection, examples
Note:
The measuring line shield can, where required, be
connected to SHIELD.
Where better HF contact of the shields is possible
at another point in the casing, there should be no
additional connection to SHIELD on the module.
2VF100069DG00.cdr
Floating sensors
Connection via 2-pole, shielded cable (IN+/AGND). In the case
of floating sensors, at least one of the measuring inputs (IN -)
must be bridged to AGND
The cancellation of electrical isolation brought about by the bridge is absolutely
necessary as capacitive signal couplings with impermissibly high common mode
voltages are already built up because of the very high impedance inputs. This
leads to sporadic incorrect measurements which are difficult to detect in most
cases.
2VF100066DG00.cdr
Potential-afflicted sensors with auxiliary power connection
Connection via 2-pole, shielded cable (IN+/IN-). Sensors with
auxiliary power supply but without electrical isolation should be
operated from the same power supply source as the module.
The sensor is connected to the two measuring inputs IN+ and
IN- in the required polarity. The AGND connection of the module
remains open.
It is to be ensured that the potential equalisation via the common supply and
sensors actually occurs.
2VF100067DG00.cdr
Sensor connection using internal module reference voltage
Connection via 3 or 4-pole shielded cable (IN+/IN-/U
Ref
/AGND).
Radiometric sensors (potentiometer, bridge circuits) are treated
as potential-afflicted sensors.
The auxiliary power is also carried in the measuring line.
If only one measuring input is needed, as in the case of the po-
tentiometer connection, the free input must be bridged to AGND.
It must be ensured that the reference voltage is not overloaded and that the cur-
rent taken from the reference source can flow back again via the AGND connec-
tions.
2VF100068DG00.cdr