Beckhoff EL3702, Documentation

Page: 50 / 181

Mounting and wiring
EL37x2 50 Version: 3.5
To rectify this, GND
int
can in this case be connected externally with an auxiliary potential of 6 V relative to
"0 V". The resulting A/GND
int
will be in the middle, i.e. approx. 0.3 V or 11.6 V.
Example 3
In the EL3xx4 terminals GND
int
is internally connected with the negative power contact. The choice of
potential is therefore limited.
Fig. 42: Invalid EL3xx4 configuration
The resulting CMP is 23.6 V, i.e. >> 10 V (applicable to EL30xx). The EL30x4/EL31x4 terminals should
therefore be configured such that CMP is always less than U
CM,max
.
Summary
This results in certain concrete specifications for external connection with 0/4..20 mA sensors:
• We recommended connecting GND
int
with a low-impedance potential, because this significantly
improves the measuring accuracy of the EL30xx/31xx.
Please note the instructions relating to the U
CM
potential reference.
• The U
CM
potential reference must be adhered to between CMP ↔ GND
int
and CMP
ch(x)
↔ CMP
ch(y)
.
If this cannot be guaranteed, the single-channel version should be used.
• Terminal configuration:
◦ EL3xx1/EL3xx2: GND
int
is connected to terminal point for external connection.
GND
int
should be connected externally such that condition 2 is met.
◦ EL3xx4: GND is connected with the negative power contact.
The external connection should be such that condition 2 is met.
If the sensor cable is shielded, the shield should not be connected with the GND
int
terminal point but with a
dedicated low-impedance shield point.
• If terminal points of several EL30xx/EL31xx terminals are connected with each other, ensure that
condition 2 is met.
Note
Connection of GND
int
In the EL30x1/EL30x2 and EL31x1/EL31x2 terminals the internal GND, GND
int
connection
is fed out to terminal contacts.
To achieve a precise measurement result GND
int
should be connected to a suitable external
low-impedance potential, taking account the specifications for U
CM
.
In the EL30x4/EL31x4 terminals GND
int
is already connected with the negative power con-
tact. Here too the specifications for U
CM
must be followed.