BECKHOFF DK9222-0112-0059 - Manual (Page 6)

I/O
Measuring analog signals
Application Note DK9222-0112-0059
KL3458 8-channel analog input Bus Terminal
The KL3458 unites eight inputs in a single housing, offering the possibility to connect multi-channel sensors using single-wire
technology in a minimal amount of space. The KL3458 is suitable for externally-powered 2 and 3-wire sensors, but a connection
must be made in each case between the ground of the sensor power supply and that of the Bus Terminal node (0 V power
contact).
1-wire connection of externally-powered sensors via KL3458:
common reference potential
Necessary coupling between GND and 0 V power contact
K-Bus power supply
0 V power contact
KL3458
arbitrary
fieldbus connection
+ 24 V
GND
sensor A sensor B
Fig. 4 KL3458 connection example: for the single-wire connection of externally-powered sensors, it is necessary to couple the GND
(sensor power supply) to the 0 V power contact of the terminal node.
Bus Terminals for Live Zero signals – “differential input”
Despite the advantages in signal transmission, the connection of sensors via a current loop also has disadvantages: unlike
with voltage-based signals, consumers cannot be connected in parallel with each other. If a measured value is to be processed
in several places, a series connection of the evaluation units is necessary. Only one evaluation unit with a ground reference
can work in this series connection, all others require a differential input that does not expect a common connection of the
individual grounds.
Such a series connection is created, for example, if a measured value is not to be transmitted exclusively to the controller,
but is to be visualized via a display device (a digital ammeter installed in the control cabinet) without the intervention of
the controller. In such cases measurement via an analog differential input that does not expect a common connection of the
individual ground connections should be used.
New Automation Technology Beckhoff
For application notes see disclaimer on the last page