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Siemens
Actuators SAS.., SAT.. for valves
CE1P4041en
Smart Infrastructure
Engineering
2019-04-09
2.9
Sizing
2.9.1
Parallel operation of actuators
3-position actuators must have one specific controller each; refer to chapter
6.3 Connection diagrams (page 50).
Up to 10 actuators can drive in parallel on a controller output with a rating of 1 mA.
Modulating actuators have an input impedance of 100 k
Ω
.
2.9.2
Permissible cable length and wire cross-sectional area
Cable lengths and wire cross-sectional areas depend on the following criteria of the
actuators:
·
Current draw
·
Permissible voltage drop across the power supply lines
The control accuracy of the modulating actuators can be improved by using 4-wire
connections, thus ensuring that voltage drops on G0 will not distort the positioning
signal.
When determining the cable length and the wire cross-sectional area, adherence to
the permissible operating voltage tolerance at the actuator is of importance, in
addition to the permissible voltage drop across the operating voltage and signal
lines (see table below).
Product
no.
Operating voltage
Terminal
Max. permissible voltage
drop
SA..31..
AC 230 V
N, Y1, Y2
2% each (total of 4%)
SA..61..
AC/DC 24 V
G0, Y, U
1% each (at DC 0…10 V)
SA..81..
G, Y1, Y2
4% each (total of 8%)
The following criteria must be considered:
·
With modulating control, the permissible positioning signal error must not exceed
1%, the reason being the voltage drop on the G0 wire.
·
The voltage drop, caused by charging current peaks in the actuator’s DC circuit,
must not exceed 2 Vpp.
·
If the G0 line is not correctly sized, load changes of the actuator due to changes
of the DC voltage drop might lead to self-oscillations.
·
The operating voltage drop at AC/DC 24 V may be a maximum of 8% (4%
across the G0 wire).
SAS31.. and SAS81..
SAS61..
Note
Basic diagram
−
voltage
drop across the power
supply cables
