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cFP-DIO-550 update rate

Hello:

 

Does anybody know which is the update rate for the digital inputs in the FP/cFP-DIO-550?  And what about the DI-330?

 

I need to know it because I'm in need of reading digital pulses that will come from an encoder, so I wonder how fast can I detect voltage changes in the modules.

 

I know that for this kind of application you can always use a QUAD-510 module, but since we're on a very tight budget and my client already has the digital I/O modules, I'm trying to figure out if I can use them.

 

Any advice or help is appreciated. 

 

Thanks in advance.

 

Robst.



Robst - CLD

Using LabVIEW since version 7.0


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Robst,

 

Here is something I found on the subject.  http://digital.ni.com/public.nsf/allkb/22FF3A4176EF96FE862570FF00827202 

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Thanks Wayne for taking the time in searching that information, it helps me.

 

Now, Does anybody has any toughts about using the DIO-550 for reading digital pulses from an encoder?

 

We are planning to use a 500 pulses/R encoder, and the maximum speed of the shaft would be 120 RPM, so we'd had 500*120= 60,000 pulses per minute, or 1000 pulses per second, so I'd need 1000 x 2 = 2000 readings per second to detect the transitions and count the pulses. So with a 10 kHz update rate, I think I would have no problem. However, I don't know if this constant polling of the module would affect the performance on the FP Controller. The application is old, and we have and FP-2000. I don't know if it will be capable of handling the constant polling and the other tasks?

 

What are your toughts or recommendations?

 

Thanks in advance.

 

Robst.

 



Robst - CLD

Using LabVIEW since version 7.0


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My gut feel is that you are going to have a hard time making it work.  I think it is very likely you will miss pulses over time.  Is it okay if you miss occasional pulses?  What kind of tolerance are willing to go on your speed reading in the event that missing pulses becomes a more frequent occurence?
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Thanks for answering Ravens Fan. Well, it's really not desirable to miss pulses over time. The speed reading is an important part in the process. The application I'm working on is part of a bottle filler, I have an optical sensor to detect when a bottle is coming to a liquid nitrogen inyector.  The speed reading will determine how many time I have to wait after the bottle is detected by the sensor to let a drop of liquid nitrogen fall into the bottle. I think missing one or two pulses from time to time wouldn't affect me that much, but if it's more than that, then I may get in trouble.

 

So, What is your recommendation in this case? What should I do? Should I try to get a faster controller? Or a better module?

 

Really appreciate your help. Thanks in advance.

 

Robst.

 



Robst - CLD

Using LabVIEW since version 7.0


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I see that there are cFP-CTR modules that are a bit cheaper than the cFP-Quad module.  They aren't that expensive, and if the client has an open slot,  I think that would be the best way to go.  I haven't used the counter modules to know exactly how to use them.  I've used the DI and DO modules, but only for basic on/off control of relays or detection of contacts, nothing where timing is critical.  You may be able to get them to work, but I just have my doubts.

 

Another alternative would be to use an external counter device or frequency counter such as one from Omega.  Then use a serial connection or an analog input to get the value into the cFP module

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Robst,

 

As long as you don't see this app growing out of the 2000 processor, I would consider a new I/O module.  I would lean towards the encoder module because it should be able to handle more of the overhead associated with encoder signals on its own.  Less impact to 2000 processor.  That said, NI must be real proud of this module based on the price tag.  WOW.

 

My past experience is that the 20xx series doesn't have a lot of memory and is pretty slow when accessing I/O modules.  I recently tested a 2020 vs a 2220.  Each with a AI-118 installed.  The 2220 had an overall acquisition rate that was >4X that of the 2020.  The majority of that gain being just in the time it took to access the I/O module.  The more the I/O module can do for itself, the better.

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Thanks both Ravens Fan and Wayne for taking the time in checking this. Kudos for you. Well, I guess I'll try to convince the client to incorporate an additional module, preferably the QUAD-510 module. This seems right now the better option for guarantying the best performance and the correct functionality of the application.

 

Thank you so much.

 

Robst

 

 



Robst - CLD

Using LabVIEW since version 7.0


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