BECKHOFF DK9222-0112-0059 - Manual (Page 5)

I/O
Measuring analog signals
Application Note DK9222-0112-0059
Bus Terminals for Live Zero signals 4…20 mA
Integrated
voltage supply
Number of channels
Resolution
Reference ground
Connection example
Sensor supply
Optional power
feed terminal
KL3454
yes/24 V DC
4
12 bit
0 V power contact
2-wire sensor
loop-powered
–
KL3454
sensor
KL3054
no
4
12 bit
common reference
ground of all 4 inputs
2/3-wire sensor
external; terminal
as galvanic island
–
KL3054
sensor
+U
B
KL3458
no
8
12 bit
0 V power contact
3-wire sensor 2-wire sensor
KL9184 KL9186
8 x 24 V DC
8 x ground
8 x 24 V DC
KL3058
sensor
+U
B
U
B
KL3058
sensor
+U
B
Tab. 3 The measuring error of all 4 – 20 mA Bus Terminals is < ± 0.3% (in relation to the full scale value).
KL3454 | Loop-powered 2-wire sensors (“loop powered”, Live Zero)
The KL3454 4-channel analog input Bus Terminal supports the direct connection of 2-wire sensors without an external power
supply. The sensors are supplied with power directly via the evaluation unit – they are “loop-powered.” An external voltage
supply can be omitted, since the 24 V power contact is fed to the terminal points. The KL3454 digitizes current signals within
the range of 4 to 20 mA with a maximum resolution of 12 bits. The internal wiring of the KL3454 has such a low impedance
that even if the sensor reaches full scale (signal level 20 mA) the low voltage drop inside the terminal can still provide the
sensor with sufficient power. The resistance of the internal wiring (80 Ω) and the length-dependent wire resistance add up
to a total that lies significantly below the otherwise usual 500 Ω. Therefore, it is usually not necessary to impose a maximum
permissible cable length.
KL3054 4-channel analog input Bus Terminal
The KL3054 also supports the connection of sensors for 4 – 20 mA signals using the 2-wire configuration. Exclusively
externally-powered sensors may be connected, i.e. they must be supplied externally with power, since the Bus Terminal
functions as a galvanic island. Using the KL3054, analog values can be determined with different sensor supply voltages or
between components that have no common ground connection. Like the KL3454, the KL3054 digitizes the sensor signals with
12 bits.
New Automation Technology Beckhoff 5
For application notes see disclaimer on the last page