Valve Control with the ET 200S 2 PULSE module
The pressure in a tank shall be controlled with a proportional valve. To balance thermal effects in the valve, the valve is switched with a controlled current. The application example realizes the slave controller (current controller) of a control cascade whose master controller (pressure controller) supplies the setpoint for the current controller. In the example, the setpoint current value is given by an operator panel.
While the valve is powered, i.e. controlled, it should always perform a minimal jittering motion (dither frequency, common practice) to prevent the static friction from taking effect, hence improving the control behavior.
The proportional valve is controlled with a pulse width modulated 24V signal whose frequency is set to the dither frequency of the valve. The valve control as well as the measurement of the valve current is performed directly by the pulse generator module "2 PULSE" of the distributed I/O system ET 200S. The module can operate up to two valves. The PI control of the valve current with function block CONT_C is realized in SIMATIC ET 200M CPU IM151-8. The non-linearity of the valve characteristic can be compensated by means of a function block.
- No additional hardware required for creating the dither frequency
- No additional hardware required for measuring the actual current value
- Convenient controller commissioning/optimization via technology object
- The example contains reusable software blocks for your own projects
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STEP 7 Project for TIA Portal V 13
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