Sensor systems 2 AS-Interface

Masters and
Gateways
Power Supplies,
Extender, Repeaters
Safety at work
I/O Modules
Control cabinet
I/O Modules
Field application
Analogue modules
Other modules
Inductive sensors
Photoelectric
sensors
Rotary encoders
Accessories
AS-Interface actuator module
214
Notes
VAA-4A-G5-V2-Ex
Valve coupler:
The block diagram at right illustrates the combined effect of the module and a valve switch.
The module, with respect to the valve, provides a power source with internal resistance. The
input circuit of the valve corresponds to the load resistance R A of this circuit. Minimum currents
and voltages must be available on the valve in order for the valve to switch correctly.
The voltage U RL drops across the cable resistance R L due to the current I RA, which is the
same throughout.
G
R i
U A/ I AK
G: Generator
R i : Internal resistor
R L: Lead resistance
R A: Load resistor
U A0 : Quiescent voltage
U A : Output voltage
U RL : Voltage drop on
lead resistance
U RA : Voltage drop on load
U 0: max. voltage
I 0 : max. current
I AK : Short-circuit current
I RA : Load current
R L
U RL
I RA
R A URA
The output characteristic diagram at right shows the generator characteristic and the resistance
line of the valve. The difference between the U RA and the actual output voltage U A
meets the maximum voltage drop across the cable. From that, the maximum cable length and
resistance can be calculated.
However, the calculation does not take into account the requirements per DIN EN 50020
(Instrinsic Safety).Therefore, the user should test the system to ensure that maximum values
for external inductance and capacitance are not exceeded.
U
UO UAO UA URL URA Output characteristic
E: Curve angle point (U E/I E)
Output characteristic
I RA I AK I O I
unpermissible area for valves
Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
Pepperl+Fuchs Group Tel.: Germany +49 621 776-0 USA +1 330 4253555 Singapore +65 67799091 Internet http://www.pepperl-fuchs.com
E
Issue date 2004-11-19 - Catalogue AS-Interface 2004/2005