Download Getting Started - Digital Control Valves - Series D636 to

7 Adaptation to special applications
Pressure control
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Getting Started Digital Control Valves
Installation
I
p
Fieldbus
communication
analog signals
electronics
Fieldbus,
Device Control
Pos
Valve
p and p/Q
control
Special Applications
PLC
Figure 17: p and p/Q control
• Pressure controller (configured by user)
 Chapter "7.9 Pressure control", page 40
• Spool position (Q) / pressure (P) switchover
 User Manual "Firmware", Chapter "7.7 Spool position (Q) / pressure (P) switchover"
Diagnostics
Control mode Δp - Control
Control mode Δp is not an independent control mode. It is just the possibility to calculate the
control variable for the pressure controller out of two pressure signals.
For instance:
To get a better performance of an hydraulic axes, cylinders are operated between two control
edges: A control edge and B control edge. Both chambers of the cylinder are always under
pressure.
MoVaPuCo
To control a value which is proportional to the hydraulic force of the cylinder, the pressures of both
cylinder chambers have to be taken into account according the cylinder areas.
PressureActualValue_EFFECTIVE = Pressure_on_A_side – ( α ⋅ Pressure_on_B_side )
Where α is the area ratio of the cylinder.
In order to use this feature the cylinder dimensions/area ratio needs to be given (index#sub-index
0x585F#00, 0x585D#00, 0x585E#00). This allows the valve to calculate an area compensated
pressure coefficient α.
2
2
Example
Applications
D Actuator – D rodB
α = ---------------------------------------------------2
2
D Actuator – D rodA
The <Pressure Actual Value> index#sub-index 0x6381#01 always refers to the pressure
difference stated above. Similarly the pressure setpoint refers to the desired Δp.
Application Instruction DCV (CDS45379-en; Version -, August 2015)
49