Beckhoff EL3182, Документация

Страница: 38 / 145

Mounting and wiring
EL3182 38 Version: 1.2
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
int
potential in common.
• the common GND
int
potential (A)
◦ is connected for 1 and 2 channel terminals to a terminal point and not with GND
PC
(power contact).
◦ is connected for 4 channel terminals with GND
PC
• 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
CM
voltage (common mode) refers to
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
CM
specifications must be followed.
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