High scaling numbers produce a flat line output

[craftsmanatlarge]

Hi, I am trying to set up our new DAQ system with Labview 8.2 a pci-6224 and a scc68 connector block recieving signals.  My problem is when I set the scaling numbers for the y=mx+b into the set-up some of the slopes are big numbers (i.e. wind speed from instrument is a 0-5volt signal representing a 0-224mph wind speed)  With the scaling number of 224 inserted and the test feature run, the diplay flat lines at ~9.5mph and never changes.  I am able to watch the voltage vary as well as another monitor vary, but the graph display just flat lines at 9.5 and never moves.  If I rescale with arbitrary numbers (i.e. 2 insted of the proper 224) I get a display that varies along with the other display in line with the signal cable.  Of course the scaling is incorrect but it does vary.  This also happened on two other channels as well that have high, two or three digit scaling numbers.  Tech support got me off the phone and promised to find an answer and E-mail the solution, but it didn't take her long to bail on me saying she's kicking herself because she can't find an answer.  Maybe Labview won't work in my situation but I need to know because this system needs to work by next wed or I put the old un-supported Labtech Notebook pro back online and return the Labview and harware for a refund.  Anyone have a suggestion for me?  Thanks in advance for reading this.

Rich

[CoastalMaineBird]

I set the scaling numbers for the y=mx+b into the set-up

Into WHAT set-up? Are you writing your own program, or using an example?

0-5volt signal representing a 0-224mph wind speed) With the scaling number of 224 inserted

If you're doing y = Mx + B, then M should be 224 / 5 or about 44.8. Again where are you putting these numbers?

the diplay flat lines at ~9.5mph

9.5 MPH / 224 = 42 mVolts. No magic number there.

9.5 MPH / 44.8 = 212 mVolts. Is it possible you've selected a 200 mV range?

Is it possible you've hooked your channels up single-ended, but are asking for differential measurements?

Or are asking for RSE when you should be NRSE, or vice-versa?

[craftsmanatlarge]

Thank you for the question about RSE vs NRSE.  I do not know which my signal should be configured for.  I currently have 11 channels of signals.  Some are voltage and some are current loops.  With my new system I have had to send all signals to 5B modules that are set up as either voltage or current for the input, and all output 0-5volt.  When I tried configuring the inputs in MAX before the signals were attached it would allow only 4 channels to be set up as differential so I checked the doc's and as far as I can tell(I'm probably wrong) the inputs should all be RSE(the signal cables are sharing a ground with the excitation voltage at thier physical location but the sig+/- travels several hundred feet to the collection hardware).  This system is an existing one that I seem to have adopted since it's Father decided he wanted to Retire.  I guess that I am not totally clear on the RSE, NRSE and Differential input setup.  I did think to ask the Tech rep about RSE and she said it should be fine as is.  I really like the software, just need to learn how to use it.

[CoastalMaineBird]

If I were you, I would back up a bit and try for one and only one channel. Your cable will tell you if you need single ended, or differential. If you have ONE wire + ground, you use single-ended, if you have TWO wires + ground, you use differential. That's assuming someone chose the right cable for you.

If you have a signal + and a signal -, you have differential. And if you are sending it several hundred feet, that's the best.

I suggest you disconnect everything, then get a single transducer with a foot or two of cable, and work with that until you get the settings right. Once you get one channel working, get a second transducer with another foot or two of cable, and get them both working.

After that, you should be able to go whole hog.

[craftsmanatlarge]

I didn't answer your question about where the offset and gain were inputted.  They were put into MAX as I was setting up their channels.  And yes the 44.8 is correct.  44.8*5volts equals 224 MPH and that is where the problem comes in.  When the voltage input is hovering around (today's numbers used here) 0.5 the speed should indicate ~ 22 MPH but the test window in the DAQ assistant reads ~9.5 MPH and is flat lined.  I am lost.

Thanks

Rich

[TCPlomp]

Hi Rich,

if you are using MAX you should set your scale to the actual physical quantities (eg 225 MPH (just to nag, why not the SI m/s?)).
I think you limit your scale to 10, taht is why you get 9.5 MPH as maximum value!

Ton

[CoastalMaineBird]

Can you put in 0.1 V? What is the MPH output?

Can you put in 0.05 V? What is the MPH output?

If #1 is twice #2, then you at least have a connection, and your problem is range / scaling.

If not, then you have a wiring / Diff/ RSE / NRSE problem.

[Rudi_N]

Craftsman:

It is very important you understand the difference between Diff/ RSE/ NRSE Input Configuration. Each one of the input configuration has a different pin assignment. Here is a document that discusses this further details. Please go through this and let us know what you find after putting 0.1 V and 0.5 V into the system.

Best Regards,

Rudi N.

[craftsmanatlarge]

Hi all,  Thank you for all of the replies.  In testing that channel with a calibrator we still could only get a flatline displayed.  We went back to the sending unit and reprogramed it for a 0-100 mph output and scaled that channel for that input and bravo she works.  That problem is now fixed as long as we do not need to read winds faster than 100mph but I am guessing that if the wind was that fast we wouldn't be here to watch it anyway.  Again thank you all.  Rich

[Rudi_N]

Craftsman:

It is great to know that the issue is now resolved. Feel free to post again if you need further assistance.

Regards,

Rudi N.