Beckhoff EP3356-0022 Documentation page 85

Example: Measuring range 0 to 10 V and measuring error < ± 0.3 % full scale value → maximum deviation
± 30 mV in the permissible operating temperature range.
Notice: since this specification also includes the temperature drift, a significantly lower measuring error can
usually be assumed in case of a constant ambient temperature and thermal stabilization of the device. This
applies equally for analog output terminals/boxes.
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. 78: Single-ended/differential typification
Notice: 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.
EP3356-0022 Version: 1.1.0
Commissioning/Configuration
85