Electrical Engineering Project Problem

My project is to control a pressure reducing valve from 3000psi to 10psi using a program call LabView. Really all I need to do is run the
proportional amplifier card which runs from 0 - 10VDC. I keep running around in circles trying to figure out what LabView actually outputs and how to change that output to 0-10VDC. So the RS232 only sends one bit at a time, good old 1's and 0's. I am using a standard 9 pin serial connector. Is the signal from the computer digital? I would think it would but but I couldn't find a definite answer. Because I know the amplifier card requires analog. Anything you can tell me would help.
Thanks,
Casey
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You need a DAC, a digital to analog converter. LABView supplies these in many forms. Go to the National Intruments web site and get out your wallet. They don't give them away.
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I believe you need a serial RS232 to analog voltage converter module. An Internet search will show many choices. There are other digital links also available. I do not know if LabView supports USB, firewire, ESATA or WiFi; but they are also helpful digital links, with the appropriate external interface module, for I/O conversion. In addition, an analog interface I/O PCI card can directly provide DC voltages; maybe your computer is already provided with a suitable one.
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When you've fixed the hardware make sure you add a small integral (reset) action to the feedback controller. If you don't you will get an offset from your desired 10 psi setpoint. Trying to make this offset smaller by just increasing the amplifier gain is a bad idea (risks instability and will never make it zero.) Do a search on "PID control" but you don't need the differential term in this application. Cheers, Roger
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