In a research setup a hydraulic circuit is constructed to mix two flows. The mass flow is controlled by a pump driven by an asynchrone motor. The mass flow is measured by a special mass flow sensor. The sensor output is relaid through the fieldpoint system to a pc with labview. We want to use labview to control the pump. Can this be done?
When you say asynchrone motor, I assume you mean something like an induction motor with a variable speed drive. If the motor drive has an input for velocity control (ex. 0-5V, 0-10V, etc.), then you could use an analog output card or analog output Fieldpoint module to control the speed of the motor. Just use the mass flow readings from the Fieldpoint unit to calculate and update the voltage sent from the analog output device to the drive. If you are already familiar with communicating with Fieldpoint devices, then adding an analog output module should be relatively straightforward.
If the motor you h ave is more like a servo motor and the drive operates only in torque mode, then the NI 7344 would be a better choice. The 7344 has an onboard veloity controller that can receive commands from LabVIEW.
Brent R. Applications Engineer National Instruments
I would like to design a closed loop regulation for a hydraulic system. I have 2 valves that control the pressure regulation which is controlled by a control amplifier (or combined volumetric-flow pressurefunction), and a cylinder with one piston to give a normal load/force (kN). One quartz force transducer is connected to the cylinder and converts the force into a charge which is then amplified by a charge amplifier. Then the charge amplifier sends to the PC a voltage. To steer pressure control, there is a slave card with settable parameters for the control amplifier for pressure control. So, the idea is to make a feedback thanks to the force transducer, and to adjust when the load is not reached, the valve open and do loops, incrementaly until the final load is reached.
Could someone help me to choose, if needed a "pressure controller", and advise me on how to proceed, should I used a PID loop control VI, and which one...?
There are about a zillion ways you could do this. You could use a DAQ board to read in the analog signal and send commands to your motion controller you mentioned in your other post. http://forums.ni.com/ni/board/message?board.id=240&message.id=2371#M2371
You could also close the control loop using the A/D converter on a motion control board, but this loop is then closed in software, NOT in hardware on the motion control board.
There is a LabVIEW PID toolkit you may want to look into.
Nicholas C National Instruments Applications Engineering