Labview 10---The signal split nodes are not working right! HELP!

[pistonbones]

I am new to labview. I have experiecne in ladder diagrams and datalogger setup and maintenece. However there seems to be an issue with my programming.

I have a NI9205 analog input modeule in a single e-net bed. I am trying to input 5 differenctial voltage signals, all with differnt scaling and all with individual user diaply gauges. Everything I've read says this process should be easy but I've gone round and round with signal split, the signal sort assistant and even some comporators. With the siganl split I get a reposne from all the visual gauges, no matter which input i have powered. I have also attempted to use MAX but my experience doesnt allow me to coplete the process.

To review: I'm trying to input five 0-5 vdc signals from five sepreate analzyers all with differnt scales. I need to siplay the realtime values to the public using five sperate gauges. PLease help!

[RavensFan]

Please post a VI so we can see your programming.  It is kind of hard to give you any pointers when we can't see what you are doing.

PS.  Please run spell check before posting your message.

[pistonbones]

Spell check got it, thanks. Unfortunately I am unable to post the VI because it on my computer at work. When I get back to work I'll post what I have. 

I realize it's hard to answer without the visual but does this problem make sense? Has anybody come across the same thing?

[Dennis_Knutson]

No, the problem does not make much sens. I have not heard of any problems with the slit signal function.  With just that function, all of your displays are going to be written since the DAQ device is acquiring from all 5 channels. Don't understand your comment about 'which input i have powered'.

[pistonbones]

Okay so this is the an example of the VI. As I said before If I put 5 volts into any of the inputs on the 9205 all the gauges connected will respond. In the daq assistant I do have 7 analog outputs added in the voltage channel area (Voltage_0, Voltage_1..ETC).

[pistonbones]

Thats my confusion I am only powering one input at a time not all five right now and all th gauges repsond. Are you telling me thats normal.

[Dennis_Knutson]

I still don't unerstand what you are 'powering up'. Some sort of sensor connected to the inputs? If you have a signal connected to only one input and are still scanning the unconnected channels, then seeing a signal on the unconnected channels is normal.

[pistonbones]

I have one analyzer (Carbon monoxide) ambient monitor connected to input #2 on the 9205, using (differential) 0-5 volts, scaled to 0-10 ppm. When the Co analyzer outputs full scale 10 ppm (5 volts), then all the gauges connected on the output side of the signal split (see the example VI.png above) respond to the one analog signal input on input #2. Yes, I am scanning other channels, however should they also respond to the one voltage signal present on input #2. All of the other inputs are disconnected and have absolutely zero voltage on them (wide open).

I must admit I'm a little discontent with this product, it boasts ease of use using graphical programming and I'm not sure how much easier it can be to input voltages and display the readings. Yet, Im having a heap of trouble and no one seems to have a solution. Well if your reading this, maybe you can help?

Thanks

[johnsold · Accepted solution]

Open inputs have some capacitance which can charge up to a value near that of the driven input.  This creates cross-talk between channels.

Try grounding the unused inputs.

Also, it is likely that your 0-5 V output from the CO analyzer is single ended, not differential.  Look at the manuals for the instrument and the DAQ device to see if you are connecting properly.

Lynn

[pistonbones]

Thank you, I will wire the unused inputs to com and see if that works. All of our ambient instruments are differential voltage outputs. I can try the other way, the only problem will be the two channel NOy monitor. Thank you for the response, cross talk does make since and I was unaware this could happen. I am used to leaving my other inputs open on our field loggers, without any cross talk.