How to control peripheral manufacturing plant

[olsonj112]

I have an control application that I hope to be able to use the parallel port to control. The plant is a model of an industrial process system with simple on/off sensors and on/off actuators. I hope to be able to input 7 sensor signals and output 5 actuator signals via the parallel port. The sensors will be changing non-deterministically and will be polled continously in order to change the output actuators. Based on my research into LabVIEW I believe this will work; however, our computer support group has not been able to install LabVIEW on my machine yet. I've looked at the tutorials available but want to verify the validity of my application with the material available from NI. My question is, Does this application seem reasonable to be done using LabVIEW? I've looked at the tutorials available but want to verify the validity of my application with the material available from NI. I've spent too much time finding a way to do this, to end up going down yet another dead end road. BTW, the machine I use is Windows 2000 with LabVIEW 7.0.

Thanks in advance.

[Buechsenschuetz]

There has been a similar question recently, and a NI guy recommended to check this document:

http://zone.ni.com/devzone/conceptd.nsf/webmain/72c6fc6ce4ad4d1386256b1800794596?OpenDocument

You probably will need some additional hardware, since it is recommended to use isolated inputs and outputs when connecting a computer to an industrial environment. I think interface modules with optoisolators for the input channels and relay contacts for the output channels will be available from NI and other manufacturers.

However, since some PCs have non-standard printer interfaces and since direct interface programming is difficult (if not possible) with WindowsXP, maybe a dedicated I/O board will be more useful. Some of these offer the features (isolated inputs/outputs) on board, I think, so in this case all you will need to connect your PC to the outer world is a break-out box or board.

[Tim Norris]

I've had some success with this kind of thing under XP so it isn't impossible as long as you use the on-board parallel port. I needed more than 8 output lines so I added a second parallel port as a cheap option to buying a DAQ card. What I found was that if I used a PCI plug in card I could control it bitwise under XP and Win98 but if I used a USB-parallel converter I could still do this under Win98, but XP wouldn't give me that degree of control.

A second consideration is how fast do you need to switch/monitor these lines? Depending on what else is running on my machines I was unable to achieve anything faster than about once every 70mS.

Like Buechsenschuetz I strongly recommend isolation or at the very least buffering with something like a 74HCT244.