Siemens Sinumerik 840D Series Function Manual page 246

A Hydraulics
A.1 Servo solenoid valves
Hysteresis,
response
sensitivity, range
of inversion
Hysteresis
Q
Fig. A-12 Hysteresis, response sensitivity and range of inversion of servo solenoid valve
Filtration grade
A-246
These three terms define similar properties.
Hysteresis means the greatest difference in the input signal for identical output
signals on passing through a complete signal range.
For a servo solenoid valve, the hysteresis is caused by:
S
mechanical friction,
S
magnetic hysteresis of the electromagnetic signal transducer and
S
the play between transmission elements.
The position control corrects the hysteresis.
The hysteresis for Rexroth servo solenoid valves is less than 0.2% and is com-
pensated for in the closed control loop.
The terms Response sensitivity and Range of inversion refer to the signal level
required to set a valve in motion again after it has stopped. The values of these
characteristics correspond to about half the hysteresis.
To overcome residual hysteresis or initial valve friction, a friction compensation
function can be activated in the HLA module.
Response sensitivity
Q
U
To maximize the service life of the control edges, thus ensuring the quality of
zero overlap, a degree of purity of the hydraulic medium (fluid) must be main-
tained.
The objective is contamination class 7...9 to NAS 1638. This can normally be
achieved with a pressure filter β
SINUMERIK 840D/SIMODRIVE 611 digital, HLA Module (FBHLA) - 10.03 Edition
Range of inversion
Q
U
=75.
10
 Siemens AG, 2003. All rights reserved
10.03
U