Mounting and wiring
EL37x2
47
Version: 3.5
5.10
Configuration of 0/4..20 mA differential inputs
This section describes the 0/4..20 mA differential inputs for terminal series EL301x, EL302x, EL311x,
EL312x and terminals EL3174, EL3612, EL3742 and EL3751.
For the single-ended 20 mA inputs the terminal series EL304x, EL305x, EL314x, EL315x, EL317x, EL318x
and EL375x they only apply with regard to technical transferability and also for devices whose analogue
input channels have a common related ground potential (and therefore the channels are not to each other
and/or not to power supply electrically isolated). Herewith an example for an electrically isolated device is the
terminal EL3174-0002.
Technical background
The internal input electronics of the terminals referred to above have the following characteristic (see
Fig.
[
}
47]
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. 37: Internal connection 0/4..20 mA inputs
The block diagram for a 2 channel terminal shows the linked GND points within the terminal (
Fig. [
}
48]
Internal connection for 0/4..20 mA inputs of a EL3xx2
):
Summary of Contents for EL3702
Page 2: ......
Page 6: ...Table of contents EL37x2 6 Version 3 5...
Page 83: ...Commissioning EL37x2 83 Version 3 5 Fig 92 Incorrect driver settings for the Ethernet port...
Page 142: ...Commissioning EL37x2 142 Version 3 5 Fig 184 Process data tab SM0 EL37x2...
Page 143: ...Commissioning EL37x2 143 Version 3 5 Fig 185 Process data tab SM1 EL37x2...
