Fig. 145 Se And Diff Module As 2-Channel Version - Beckhoff EL3692 Documentation

Commissioning
Single-ended/differential typification
For analog inputs Beckhoff makes a basic distinction between two types: single-ended (SE) and differential
(DIFF), referring to the difference in electrical connection with regard to the potential difference.
The diagram shows two-channel versions of an SE module and a DIFF module as examples for all multi-
channel versions.
Fig. 145: SE and DIFF module as 2-channel version
Note: Dashed lines indicate that the respective connection may not necessarily be present in each SE or
DIFF module.
The basic rule:
• Analog measurements always take the form of voltage measurements between two potential points.
For voltage measurements a large R is used, in order to ensure a high impedance. For current
measurements a small R is used as shunt. If the purpose is resistance measurement, corresponding
considerations are applied.
◦ Beckhoff generally refers to these two points as input+/signal potential and input-/reference
potential.
◦ For measurements between two potential points two potentials have to be supplied.
◦ Regarding the terms "single-wire connection" or "three-wire connection", please note the
following for pure analog measurements: three- or four-wire connections can be used for
sensor supply, but are not involved in the actual analog measurement, which always takes
place between two potentials/wires.
In particular this also applies to SE, even though the term suggest that only one wire is
required.
• The term "electrical isolation" should be clarified in advance.
Beckhoff IO modules feature 1..8 or more analog channels; with regard to the channel connection a
distinction is made in terms of:
◦ how the channels WITHIN a module relate to each other, or
◦ how the channels of SEVERAL modules relate to each other.
The property of electrical isolation indicates whether the channels are directly connected to each
other.
124 Version: 2.1 EL3692