SCC-2350 power requirements and module configuration

[Thibault_Prevost]

I inherited an SC-2350 board with an SCC-PWR 01. The board is connected to a laptop via the DAQCard-6036E and receives its power directly from the laptop. I'd like to hook up 3 devices to the system: a force sensor (5VDC excitation), an LVDT (6-30VDC excitation) and a voice-coil linear motor. The modules I currently have are SCC-FT01, SCC-SG04 and SCC-SG24.
Questions:
    1) my force sensor needs a 5 VDC excitation, so none of the modules seems really appropriate... I thought I could somehow use the 5VDC output from the SCC-PWR01 (which has a 5VDC block terminal from what I could see) but the output from the power module as measured with a voltmeter is rather close to 0. Is the use of an external 5VDC power supply the only option to excite my load cell?
    2) the SCC-SG24 module should work with the LVDT. Just one problem: it seems that I can only plug in one SCC-SG24 to the board (whenever I plug in the second one I have, the excitation output of the first module drops from 10V to 0...). Is it because I am power limited?
    3) the motor I have should be current driven. I tried to output a sine current wave to it via one of the two analog output sockets and module SCC-FT01 using a basic vi program with a DAQ assistant generating a sine signal. I varied the signal amplitude by a few orders of magnitude from 1mA to 1A but the motor did not respond... I switched to voltage mode but no response either. The wired connection to the motor seems perfectly alright since the motor does respond to an external sine signal generator. Do you know what could be wrong in the setting/configuration of the device/module?

Thanks for your help!

Thibault.

[Vanessa L]

Hi Thibault,

Thank you for posting.  Since your force sensor needs a 5VDC excitation, you are going to need a module that specifically outputs a DC voltage for excitation.  You are correct that since your SCC-SG04 provides a 2.5 VDC excitation voltage and the SCC-SG24 provides a 10 VDC excitation, the modules that you have will not work.  Since the SCC-PWR01 is outputting a power level and not the correct excitation voltage for your force sensor, you are probably going to need some other source, maybe a different module to provide the 5 VDC excitation. 

I'm not sure why the second SCC-SG24 module would be causing the excitation voltage of the other module to decrease.  Have you tried switching the modules to see if the the same thing occurs if you add them into the system in a different order?  How are you testing that the excitation voltage has decreased?  You should not be limited by the power that the SCC-PWR01 provides because the SCC-SG24 module takes that 5 V and converts it to 15 V so all the modules in the carrier have access to a higher power.  This is described further in this knowledgebase. 

Finally, in order to drive current into your motor you might need one of NI's devices that can actually output current.  This knowledgbase talks about what devices NI has that can output current such as the SCC-CO20  module that can provide up to 20 mA of current.  If you could get the device to respond to an analog output wave of voltage, there is a possibility that your LabVIEW program is not doing what you think.  If you try to read the value on the output channel of the feedthrough module with a DMM, are you actually getting something to register? It would be best to first test the hardware by tying to output a voltage to your device in Measurement and Automation Explorer.  By using Test Panels, you can try outputting a varying signal on the hardware to see if the motor responds.  If it still doesn't work in Test Panels, there may be something wrong with the hardware or the way you are connected.  Otherwise, you can narrow down that the software program was not functioning. 

Please let me know if there are any other questions that you have!

[Thibault_Prevost]

Thanks for your response: this is is very helpful.
I grossly measured the output values on the feedthrough module using a multimeter and it seems that the output voltage sine variations match the commanded Labview signal but I still get no response from the motor. I further tested the motor capabilities using an external power supply and it seems that 100-900mA current amplitudes are required to put the motor into motion (!) - a low-current voltage sine wave is definetely not enough. I guess the SC-2350 board I have is not able to provide 100-900mA currents, is it? Would you have any suggestion on what I could possibly do as an alternative?

Thanks again!

Thibault.

[Vanessa L]

Hi Thibault

You are correct in saying that the modules that you currently have will not be able to source 100-900 mA of current.  Unfortunately, none of our DAQ cards have specifications more that 4-20 mA.  This is limited by the amount of voltage that can be supplied due to the power limitations of the card plugged into the PCI bus.  The workaround for you would involve needing a servo drive with an external power supply.  This would be able to convert analog output voltage to current in order to drive your motor with the amount of current that you need.  There is a DevZone tutorial on our website that talks about the Fundamentals of Motion control.  This has a diagram that describes the different components of a motion control system. If you look at the diagram, it is necessary to have a motion controller that outputs a voltage and then the amp/drive will convert that voltage to current to drive your motor.  In your application, if you are just interested in driving the motor and you don’t need any feedback control, you should be able to use the analog output of your 6036E DAQ card and then feed that into a servo drive to convert it to current.  However, if you need precise control and feedback, you will probably need one of our motion controller cards (733x, 734x, and 735x series).  Here is a link to the website page for NI Motion Hardware that should give you more information about both our motor drives and motion controller cards.  Hopefully this information will be helpful!

Message Edited by Vanessa L on 11-21-2007 10:11 AM