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ni9505 inductance

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Hello,

 

First of all thank you for your time and attention . I have some doubts regarding NI9505 . Here is my list of questions:

 

  1. I want to use a motor with an inductance of 82uH (http://www.maxonmotor.ch/e-paper/  page 82 (RE40)) , but in the specifications says that the minimun inductance for the current sense is 500 uH (page 27 from Specifications) , will i be able to read the correct value of the current with the NI9505 or i will need to use another method ?
  2. I'm currently working with an old DC motor and the NI9505 , so i dont have the motor values as there is no datasheet in internet for this motor , but the values that i'm taking are very strange , for example :

Duty cyclePower Supply(Current Display)Current Feedback(NI 9505)

 

25%50mA10

 

50%60mA3

 

75%70mA4

 

100%77mA5

 

So my question is , why on DC =25% there is more currrent than it 100% , and what are the units of the current sense ?

 

I am using the modification of current sensing of this page : http://forums.ni.com/t5/Real-Time-Measurement-and/How-is-the-NI-9505-current-sense-measured/m-p/8194... with the open loop example ( i have attached the vi i'm using ) .

 

Thanks once again for your attention , any kind of help would be appreciated .

 

Regards,

 

Albert

 

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Hi Albert,

 

Thanks for your post. Regarding your 1st question about interfacing a RE40 82uH motor with the NI9505 (which requires 500uH for current sense) I would like to refer you to the KB article here which refers to using the MID-765x Drive with Low Inductance Motors. Although this is a different model power drive the principles described should be the same, I would also recommend researching the implications of using inductors in series with motors before considering this solution.

 

Can I also refer you to the forum here which details a similar configuration.

 

Regarding the reasons behind the strange behaviour you are experiencing with the old DC motor my initial thought is that this is also due to the current sense specification for the NI9505 not being met.

 

Hope this helps with your proposed application.

 

Thanks

 

Jamie S.

Jamie S.

Applications Engineer
National Instruments
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