Digital Power Amplifier
Series VRD350 and VRD355
Installation Manual
25
IA VRD UK.INDD RH 02.06
Parker Hannifin GmbH & Co. KG
Hydraulic Controls Division
Example: E8 = 1 constant rise rate
S1 = 8.00V; S2 = 2.00V; S7 = 6.00s
3.3. Offset
Any drift of the drive can be corrected by the off-
set parameter P1. This functions as an additional
command signal. If the assembly is operated on
NC axes, the positioning can be adjusted to 0. The
value changes in steps of 5mV, display shows every
second step in 10mV stages.
3.4. Valve Curve Linearisation
Five curves are available for linearisation of the
flow characteristics of different valves:
Valve curve 1: General NC curve, based on experi-
ence.
Valve curve 2: Linearisation of NG6 proportional
directional valves with flow char-
acteristic P012 and P020.
Valve curve 3: Linearisation of NG6 proportional
directional valves with flow char-
cateristic P006.
Valve curve 4: Linearisation of NG10 proportional
directional valves.
Valve curve 5: Linearisation of proportional pres-
sure valves.
3.5. Adjustment of Current Gain
Current gain can be set independantly in param-
eters P3 (negative command signals, for solenoid
A) and P4 (positive command signals, for solenoid
B). (e.g. balancing for differential cylinders)
3.6. Dither
The dither signal can be matched to the valve by
parameters P5 (amplitude) and P6 (frequency,
stepwise adjustment). The dither signal reduces
the hysteresis of spool movement. Generally, low
frequency signals are more effective, however they
may result in noticeable disturbances (noise, oscil-
lations). Values between 80Hz (for systems with a
low natural frequency) up to 327Hz (for systems
with a high natural frequency) are recommend-
able. Sensible values for the amplitude are within
the range 0.20V to 1.2V. The dither signal reduces
the RMS value of the current noticeably at 10V
command signal.
3.7. Current Controller
Each solenoid is driven by a pulse width-modulated
signal with rapid de-energisation. The solenoid
current is measured and compared with the com-
mand signal in a controller with a PI-characteristic.
The controller setting can be adjusted separately
for rise and fall in the current through parameters
E4 to E7.
3.8. Output Stages
• Output stages of PWM type are used to reduce
powerlosses.
• The pulse frequency is approx. 1.35 kHz.
• Output stages are equipped with over ener-gisa-
tion and high-speed de-energisation to increase
the dynamic response.
• Output stages are designed for solenoids up to
3.5 A.
• The particular solenoid type used is set with
parameter E3 without any hardware changes.
• Standard settings are available:
E3 = 1 3.5A solenoid; NG10 proportional di-
rectional valves, direct controlled
E3 = 3 2.7A solenoid; NG06 proportional
valves, standard
Affects both internal command signals
S1 to S4 as well as external command
signals SW5 and SW6.
Factory settings should only be changed
in exceptional circumstances after con-
sulting with the manufacturer.