Three controller blocks are available:

• PDI controllers (digital and analougue)
• Analogue gain (a pure gain useful during model set-up)
• Distributors controller (On-Off)

In addition also the following blocks are present:

• Analogue to Digital converter
• Digital to Analogue converter
• Position transducer
• Antialiasing filter

The PDI is the model of a digital or analogue controller with Proportional Derivative Integrative logic. The feedback signal is read each sampling time, the output current is generated with a delay equal to the calculation time. The integrator current is limited between a minimum and a maximum value; the integrator input is null if the position error is between the minimum and maximum thresholds; the threshold values shall be expressed in the position error unit; on the derivative branch there is a first order filter. The control is not operative if the system pressure is lower then a threshold. A block diagram of the control logic is reported in the following figure; the gain can differ for positive or negative current.

The analogue gain is a pure gain; this block can be used to increase the simulation speed; the inputs and the output are the same of the PDI block.

Also the distributor block has the same inputs and output; this block shall be utilised in conjunction with the distributors (On-Off valves), so the current value will have the maximum value if the position is different from the demand and zero value when the demand position is reached.

The Analogue to Digital converter can be utilised to take into account the effect of the resolution on the feedback signal.

The position transducer allows to take in account the effect of a backlash.

The antialiasing filter is a second order filter generally used in every digitally controlled system.

Each of these three blocks shall be inserted in the feedback line.

[ Previous | Next | Index ]