Dinel PDU-40-W Series, Руководство пользователя

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User manual - METER PDU-4x0-W
Figure 4.18. Serial connection of passive 2-wire sensor with PDU-4x0-W unit
and other current measurement device (e.g. PLC controller).
If device B ( Figure 4.16 , 4.18 ) is equipped with galvanic separated input or if
different potentials between
A
and
B
devices signal grounds are allowed (e.g. if RS-
485 interface is separated or unused), current loop can be closed without separator
G
.
Calculation of maximal allowable resistance of separator's input
Maximal resistance of the input (R
G max.
) and wires (R
W max.
) are calculated for circuit from
Figure 4.17
. Used symbols are described below.
U
S min.
- minimal sensor supply voltage (given in technical data of sensor),
U
g
- voltage drop on galvanic separator input (constant for 4-20 mA range of
current),
I
max.
= 20 mA - maximal current of current loop,
U
O
= 24V - sensor supply output voltage of device A,
R
O
= 3 0
Ω
- sensor supply output resistance of device A ,
R
INP.
= 50
Ω
- measurement input resistance of device
A ,
R
G max.

R
W max.
=
U
O
−
U
S min.
−
U
g
I
max
−
R
INP.
−
R
O
Let U
S min.
=12V and U
g
=5V then:
R
G max.

R
W max.
=
24
−
12
−
3,5
0,02
−
50
−
30
=
270

If current loop is closed without the separator
G
, then sum of measurement input resistance
(R
B max.
) of device B ( Figure 4.17 ) and connections resistance (R
W max.
) should be not grater
than result of given below formula:
15
!
-
+
12 11 10 9 8 7
Connected internally
G
galvanic
isolation
+
-
A
B
+
-
R
B