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SCB-68 Configuration with PCI -6220

Hello,

I'm quite new with NI products and I'm facing a huge problem for my poor knowledge 😉

 

I'm using a PCI-6220 and a SCB-68 to (try to) realise the acquisition of two signals : an accelerometer and an impact hammer. I also have a conditionner.

The problem is that I don't know on which pins I have to connect the wires of the accelerometer and the hammer.

I'd like to have the accelerometer on the channel 1 and the hammer on the channel 2.

 

I'd like to have a RSE configuration. As I have two wires per sensor, I suppose I have to connect one of them on the pin channel (1 or 2) and the other one to the ground. BUt there are several pins for the ground... Which one do I have to choose ?

 

Thanks

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Hello Sylvain,

 

 To view the device pinouts of your DAQ device you must go to Measurement & Automation Explorer >> "NI DAQmx devices" >> Right Click on "NI PCI-6220" >> "Device Pinouts, this will show you the layout of the pins on your DAQ card. It does not strictly matter which ground you connect the second lead of your sensor to, for example you can connect the accelerometer to AI1 and AIGND and your impact hammer to AI2 and AIGND. The following Knowledge Based Article may assist you further with your application.  http://zone.ni.com/devzone/cda/tut/p/id/3344.

 

Please post back with more info if necessary and I will look into this further.

 

Kind Regards

Ben L
Field Engineer
National Instruments
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Hello Ben L,

 

Thank for your quick reply!

 

I had a look into your link but I don't understand everything.

 

I will try to detail my configuration :

 - A datagate with 4 inputs and 4 outputs

 - An accelerometer

 - An impact hammer

 

The accelerometer is plugged on the input 1 of the datagate, the impact hammer on the input 2.

The outpout 1 is connected to Ai1 (pin 33) on SCB-68 and AIGND (pin 67).

The outpout 2 is connected to Ai2 (pin 65) on SCB-68 and AIGND (pin 32).

 

When I use the test pannel in MAX to see the electrical signals on each channel, I have a trouble. When selecting Dev1/ai1, I can notice a change in the signal using either the hammer or impacting the accelerometer with a finger. Same thing on channel 2...

I really don't understand...

 

Thanks again for your help

 

 

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Hello again Sylvain,

 

It sounds like a ground loop is being created in your circuit and cross talk is occuring between the transducers, this commonly occurs when using an RSE connection. The best solution for your application would be to switch to a Differential connection, for details on how to connect this up please refer to "Table 1. Analog Input Connections" in the Field Wiring and Noise Considerations KB I forwarded to you earlier. The drawback with doing this is that you will halve the channel count on your DAQ device as both of your transducers will require an additional channel.

 

In software you must also specify the Differential connection under "Input Configuration" in MAX. The 2 bias resistors in the circuit are recomended but you may not need them so it might be worth trying without initially.

 

Have a go at this and let me know the outcome

 

All the Best

Ben L
Field Engineer
National Instruments
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Hello Ben L,

 

I really appreciate the time you are spending on my problem. Thnak you very much.

The fact is that it is the first time I have to configure a NI device and I'm a bit lost. I don't understand the Table1 you are mentionning... I don't where I have to plug my wires...

 

Sorry

 

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Hello Sylvain,

Sorry about the delayed response to you last message, I have been on a course and didnt get a chance to get back to you. I have annotated the Differential connection circuit diagrams attached to detail what pins you must connect your transducers to. Initially try and connect up without the resistors, if you are still getting cross talk between channels then you will need to get hold of 2 resistors of equal value between 10k-100k to tie down to ground. Dont forget to choose differential mode in the MAX test panels.

 

Best Regards,

Ben L
Field Engineer
National Instruments
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Hello Ben L,

 

Thank you once again for your support!

 

I connected my transducers as you told me and everyhting was working yesterday.

This morning, it is not working anymore whereas nothing has changed...

I had a look into MAX and without exciting any transducer, I have a signal bewteen 0 and 10V.

 

MAX

 

I really don't understand what's happening now... So difficult to make things running.

 

Regards

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Message 7 of 19
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Hello Sylvain,

 

I hope you are well, your very welcome.

 

Well done on getting it working yesterday, shame its not functioning anymore. Can you attach the image "MAX" by clickng Add Attachments as it is not visible on your previous post, it would be useful for me to see a screenshot of this strange signal you are recieving.

 

Kind Regards

Ben L
Field Engineer
National Instruments
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Hello Ben L,

 

Sorry for the mistake, please find herewith enclosed the photo.

 

Regards

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Message 9 of 19
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Hi Sylvain,

 

You mentioned it appeared to be working fine yesterday, has anything changed in yout system e.g a cable? Also could you please list some info on your 2 transducers (Make, Model, Part No etc) so I can have a look at the expected outputs from them. I am sorry this is taking a long time to resolve but hopefully we should be able to get you up and running soon. Also did you use the 2 bias resistors for each sensor in the circuit diagram I sent you?

 

Thanks

Ben L
Field Engineer
National Instruments
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