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I am getting a lot of noise on my cDaq Ni 9201 analog input module. Seems to be coming form the network hub

I was using Fieldpoint to collect data from my testing machines, using RS232 direct to a computer. We decided to switch to cDaq-9181 chassis with Ni 9201 analog input over our intranet.

I set it all up on my desktop computer thru or main Ethernet hub.(the hardware was on one node and the computer was on another) everything looked good, so I moved it to the testing machine Area. This area of the plant has it's own Hub that is connected with fiber optic cable to the main hub. The data was corrupted. So I tried to move all the hardware keeping it all just thru the new hub. This was better but not good enough. One thing at a time I moved Them and connected them directly to the new hub. Every time the data was better, but I could not get it clear enough to use it. How can the data get noise from the network? Isn't this all digital? It looks like analog noise to me. Has any one else had this problem? And what did you do to fix it.

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Message 1 of 9
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Hi maintenanceman2,

 

I have a few follow-up questions to ask you regarding the issue you are having with seeing noise when you have your NI 9201 in the testing machine area. First, could you clarify what you mean by when you said you moved one thing at a time and connected them directly to the new hub? Also, could you let me know what kind of a signal you were expecting to receive from the hardware and also what kind of noise you are seeing when you are collecting data? Also when you move the hardware from your desktop area to the testing machine area, what all changes in the environment of the area (more hubs, longer cables, more machines around,…)?

 

Regards,

Tommy G.
Product Manager - Search
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Try using an isolation transformer between main power and the power supply to the cdaq-9181 and see if that makes a difference.

 

 

 

Randall Pursley
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What I mean is The computer was about 50 feet away from the hub and the Daq was about 50 feet away from the hub in opposite directions, with copper wire runs back to the Hub. I physically moved the computer, and connected it to the Hub with about 5 foot of cable, then I physically moved the Daq and connected it to the Hub with 5 foot of wire.

   I am looking at the 0-10 volt signal and scaling it to read 0- 1800 RPM. I hooked a 9 volt dc battery to the one input and a 5 vdc power source to another. So I was expecting a nice constant input. The 3rd input is 0- 5vdc scaled to 0 - 250 for torque, the last ones were left unwired tension should read zero ,and center dist. Should read 18. I have attached a Excel spreadsheet of the data.

   last the desktop area is my office, no machines, and the testing machine area has many machines in it, all just like this one running and collecting data with the old Fieldpoint hardware over Rs232 about 25 foot long. The copper cables from my office are about 150 feet long.

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Hi maintenanceman2,

 

Since you have a control room which you tested the DAQ hardware and saw no noise in the signal, it seems like the noise you are seeing is from the environment in the testing machine area. You said that you are using a copper wire to run the signal from the machine to the DAQ hardware, is this wire shielded at all? With a shielded cable you should see a reduction in the amount of environmental noise you see in your signal.

 

Also when you said the copper wire runs back to the hub, could you give me more of a description of what the hook-ups are here? Are you running a copper wire from your machine to the DAQ hardware and then another copper wire from the DAQ hardware to your computer? Or are you having the copper wire go into the hub and out of the hub to the DAQ hardware?

 

I have also attached the link for the Field Wiring and Noise Considerations for Analog Signals tutorial which can give you some more information about solving noise problems in measurement setups.

 

http://zone.ni.com/devzone/cda/tut/p/id/3344

 

Regards,

Tommy G.
Product Manager - Search
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Message 5 of 9
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I think we are getting off track a little. I am used to troubleshooting analog noise, and am sure I am not getting any before the Daq hardware. The wire is only 6" long properly grounded and isolated from any type of electric.

My confusion is, it seems to be getting the noise after the Hardware. Is this not a digital signal? I was not aware that once the signal was converted it could be corrupted.

When I am talking about the copper wire I'm referring to the Category 5E patch cables from the NI Daq to the Hub, and from the Hub to the computer.

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Message 6 of 9
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That is why I suggested an isolation transformer or a cleaner power source for the DAQ chassis.  Noise could be coupling into the DAQ via the power supply.  I have had some problems with the USB-based DAQ during sensitive measurement due to power supply noise/ground loop issues.  Maybe the same thing is happening to you with this device.

Randall Pursley
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Message 7 of 9
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I tried the isolation transformer with no success. The readings were just as bad as before.

Thanks for the idea. I am willing to try anything that sounds reasonable.

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Message 8 of 9
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Is the DAQ isn't configured for single-ended instead of differential?  I don't know if this would have any effect with the DAQ your are using, but I don't have any other ideas.

Randall Pursley
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