LabVIEW
generate analog current output
Hi,
Thankyou for your quick reply.
Actually the aim is to use Labview as a test simulation for a group of PLCs in an oil and gas application,so the minimum number of analog inputs to the group of PLCs (or outputs from Labview) we have now is 72,which is a huge project project.So i feel that I would require a minimum of 30 channels(analog and digital output form Labview).I am planning to use the same setup for diffrent projects,thatz why the variation in numbers
.Our software only recognises current inputs,so yes a current from 4-20mA is required for the application.
Regarding the pulse inputs to the PLC,its just needed to show that there is flow in the stream, at present we use a pulse generator giving out a variying pulse output from 80Hz to 1 kHz,but as long as there is a square pulse which can be varied in frequency,so that the flow varies,that would be great. At present we have 35 diffrent pulse inputs,so we may need like 35 pulse channels,or is there another way to do it? .Also will the digital or analog card do for this genration of pulse,or should i look for another card.
Thanks for all the support, hope that some light may hav been shed on the topic,with all these info.
Kind Regards
Joseph
With respect to the relays: It's usually a good idea to put something between your signal source and your unit under test in order to protect both sides, especially if the items are expensive. Are your analog current sources isolated? Perhaps that's what caused 3 of the card to burn out, but that's mere speculation on my part. However, you must be clear in your terminology since you're just confusing matters. The relays are not triggering the digital signals. The relays are simply passing the signal through or cutting it off. That's considerably different than using the relays to trigger a digital signal. Also, you would only need a relay if you needed to guarantee complete physical isolation when there is no stimulus. After all, when the relay is on, the stimulus is connected to the PLC, so you no longer have isolation. For true isolation you should look into signal conditioning products that use transformers or optoisolators, as those will give you electrical isolation. It's not clear to me if that's the case in your application.
Now, as far as the generation of the signal, as Hannah indicated the 6528 is also a static digital I/O board - you can usually tell by the price tag. While the M-series of cards provide timed digital outputs some of them require an external clock. I would second Hannah's suggestion and contact your local NI rep and explain your system in detail to them. For example, while the M-series of cards are not isolated, and if you need isolation, you may be able to use SCXI to give you the isolation. Again, I can't say for sure if you need isolation without doing a more detailed analysis of your system, and I'm not prepared to do that. One suggestion: resist the suggestion to completely replace your system unless absolutely necessary.
Good luck.
