Electropneumatic positioners
SIPART PS2
Technical description
6/5
Siemens FI 01 · 2009
6
The NCS sensor consists of a non-contacting position sensor. All
coupling elements are omitted such as coupling wheel and
driver pin with part-turn actuators or lever and pick-up bracket
with linear actuators up to 14 mm travel.
This results in:
• Even greater resistance to vibration and shock
• No wear of sensor
• Problem-free mounting on very small actuators
• Negligible hysteresis with very small travels.
The sensor does not require an additional power supply, i.e.
SIPART PS2 (not for EEx d version) can be operated in a 2-wire
system. The NCS (N
on Contacting Position Sensor) consists of a
potted sensor housing which must be mounted permanently and
a magnet which is mounted on the spindle of linear actuators or
on the shaft butt of part-turn actuators. For the version for travels
>14 mm (0.55 inch), the magnet and the NCS are premounted
on a stainless steel frame and offer the same interface mechan-
ically as the positioner itself, i.e. they can be mounted using the
standard mounting kits 6DR4004-8V, -8VK and -8VL.
The installation of a EMC filter module in the positioner (controller
unit) is necessary in order to ensure a connection level with EMC
according to EN 61326/A1 and NAMUR NE21 when using exter-
nal sensors (see Ordering data for "EMC filter module")
■
Function
The SIPART PS2 electropneumatic positioner works in a com-
pletely different way to normal positioners.
Mode of operation
Comparison of the setpoint and the actual value takes place
electr
onically in a micr
ocontroller. If the microcontroller detects a
deviation, it uses a 5-way switch procedure to control the piezo-
electric valves, which regulates the flow of air into and from the
chambers of the pneumatic actuator or blows it in the opposite
direction.
The microcontroller then outputs an electric control command to
the piezoelectric valve in accordance with the size and direction
of the deviation (deviation between setpoint w and control
output x). The piezoelectric valve converts the command into a
pneumatic positional increment.
The positioner outputs a continuous signal in the area where
there is a large control deviation (high-speed zone); in areas of
moderate control deviation (slow-speed zone) it outputs a se-
quence of pulses. No positioning signals are output in the case
of a small control deviation (adaptive or variable dead zone).
The linear or rotary motion of the actuator is detected by the
mounting assembly and transferred to a high-quality potentio-
meter made of plastic conductive material over a shaft and a
non-floating gear transmission.
The angular error of the pick-up in cases where the assembly is
mounted on a linear actuator is corrected automatically.
When connected in a 2-wire system, the SIPART PS2 draws its
power exclusively from the 4 to 20 mA setpoint signal. The elec-
tric power is also connected through the 2-wire bus signal with
PROFIBUS operation (SIPART PS2 PA). The same applies for the
FOUNDATION Fieldbus version.
Pneumatic valve manifold with piezoelectric valve precontrol
The piezoelectric valve can release very short control pulses.
This helps achieve a high positioning accuracy
. The pilot ele-
ment is a piezoelectric bending conver
ter which switches the
pneumatic main control unit. The valve manifold is characterized
by an extremely long service life.
Local operation
Local operation is performed using the built-in LCD and the
thr
ee input keys. Switching between the operating levels Auto-
matic, Manual, Configuring and Diagnosis is possible at the
pr
ess of a button.
In Manual mode the drive can be adjusted over the entire range
without interrupting the circuit.
Operation and monitoring with the SIMATIC PDM communi-
cations pr
ogram
The SIMA
TIC PDM program is available for communication
through the HAR
T interface and also for the PROFIBUS PA cou-
pling.
The SIMATIC PDM communications software permits easy re-
mote operation and monitoring using a PC or laptop. The posi-
tioner can also be configured using this program. Parameters
which provide important information for maintenance and fault
diagnosis of the complete unit can also be determined using
process data and comparison data.
When operating the SIPART PS2 through the HART interface, the
connection is made directly to the 2-wire cable to the
SIPART PS2 positioner through a HART modem that can be con-
nected to the RS 232 or USB interface. The signals needed for
communication in conformity with the HART protocol are super-
imposed on the current signal in accordance with the F
requency
S
hift Keying (FSK) method.
Automatic commissioning
With a simple configuration menu the SIPART PS2 can be quickly
adapted to the fitting and adjusted by means of an automatic
star
tup function.
During initialization, the micr
ocontroller determines the zero
point, full-scale value, the direction of action and the positioning
speed of the fitting. From this data it establishes the minimum
pulse time and the dead zone, thus optimizing the control.
Low air consumption
A hallmark of the SIPART PS2 is its own extremely low consump-
tion of air. Nor
mal air losses on conventional positioners are very
costly. Thanks to the use of modern piezoelectric technology, the
SIPART PS2 consumes air only when it is needed, which means
that it pays for itself within a very short time
Comprehensive monitoring functions
The SIPART PS2 has various monitoring functions with which
changes on the actuator and valve can be detected and sig-
naled if applicable when a sele
ctable limit has been exceeded.
This infor
mation may be important for diagnosis of the actuator
or valve. The measured values to be determined and monitored,
some of whose limits can be adjusted, include:
• Travel integral
• Number of changes in direction
• Alarm counter
• Self-adjusting dead zone
• Valve end limit position (e.g. for detection of valve seat wear
or deposits)
• Operating hours (also according to temperature and position-
ing ranges) as well as min./max. temperature
• Operating cycles of piezoelectric valves
• Valve positioning time
• Actuator leakages
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