Fig. 31 Internal Connection Diagram 0/4; Fig. 32 Internal Connection Diagram For 0/4 - Beckhoff EL3182 Documentation

Mounting and wiring
Technical background
The internal input electronics of the terminals referred to above have the following characteristic (see Fig.
[} 38] Internal connection diagram for 0/4..20 mA inputs):
• Differential current measurement, i.e. concrete potential reference is primarily not required.
The system limit applies is the individual terminal EL30xx/EL31xx.
• Current measurement via a 33 Ω shunt per channel, resulting in a maximum voltage drop of 660 mV
via the shunt
• Internal resistor configuration with GND point (A) central to the shunt
The configuration of the resistors is symmetric, such that the potential of (A) is central relative to the
voltage drop via the shunt.
• All channels within the terminal have this GND
• the common GND
int
◦ is connected for 1 and 2 channel terminals to a terminal point and not with GND
◦ is connected for 4 channel terminals with GND
• The center point of the voltage drop over the 33 Ω shunt is referred to common mode point (CMP).
According to the technical product data, the maximum permitted U
the potential between the CMP of a channel and the internal GND or the potential between the CMP of
2 channels within a terminal.
It must not exceed the specified limit (typically ±10 or ±35 V).
Accordingly, for multi-channel measurements U
Fig. 31: Internal connection diagram 0/4...20 mA inputs
The block diagram for a 2 channel terminal shows the linked GND points within the terminal (Fig. [} 38]
Internal connection for 0/4..20 mA inputs of a EL3xx2):
Fig. 32: Internal connection diagram for 0/4..20 mA inputs of a EL3xx2
38
potential (A)
Version: 1.2
potential in common.
int
PC
voltage (common mode) refers to
CM
specifications must be followed.
CM
(power contact).
PC
EL3182