Multifunction DAQ

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analog input cannot generate sine wave



    I am using a scb-68 daq board and working in differential mode. I have a single phase power supply connected to the daq

    (channel 68(+) and 37(-)). I am suppose to obtain a sine wave but that is not the case.  When i supply 0 volts to the daq i get a flatline 

    at a value of -10 and when i increase the voltage no change occurs. But when using RSE mode I recieve a sginal, still not sinusoidal,

    and as i increase the voltage not affect either.  May you be of guidance to me and help understand what is going on. Thank you very much  in advance




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Message 1 of 5

Hey PJ,


 First of all, what is the actual DAQ card that you are using connected to the SCB-68 terminal block? Just looking at the device pinout for the PCI-6251, the differential connections for ai0 should go to pins 68(+) and 34(-). This pinout hold true for a bunch of our DAQ boards. These number should corrospond to the SCB-68 terminal block numbering. First I would make sure to check the pinout of your DAQ board and make sure that 68 and 34 are labeled as ai0 and ai8. 


Also, would you mind clarifying the rest of your system? The way I understand it is you have some sort of power supply that is going to be outputting a sinusoid to your DAQ device. You must make sure that the voltage value of that sine wave is in the analog input range of the DAQ card. What is the power supply that you are using and how are you controlling the values of the voltage that you are connecting to the SCB-68?


Chris N White

High Speed Products Group
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Message 2 of 5

Hi Chris,


You are correct. I am using a PCI-6251 daq card and scb 68 daq board.  The channel ai0 is 68(+) and 34(-).

I am supplying constant voltage 120/208 at 60 Hz which is connected to an autotransformer in which i am controlling

(variable voltage) the amountt of voltage being given to the daq. From my understanding i can only supply about 10 volts to the

daq, please correct me if im wrong, and thats what ive being doing. But as mentioned in my first post i cannot retrieve

a sine wave. When measuring the voltage with a fluke meter the sine wave does appear. Thanks!!



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Message 3 of 5

Hi PJ,


You are correct that the input voltage range is -10V...10V, so you will only be able to supply a sine wave with a maximum amplitude of 10V. For testing purposes I would halve this and use an input sine wave with a voltage of 10V peak to peak. This puts us well inside the maximum voltage range. Next for troubleshooting purposes I would first try to measure this input in Measurement and Automation Explorer (MAX) using one of the test panels for Analog Input. This takes out any programming issues that might be getting in the way. Second, I would try to measure this voltage input on other analog input channels, just to make sure that it is not a problem with the hardware. 


My next thought is that the current that is being input to the board is above the input current threshold of 20mA. To test this is it would be beneficial just to check in the MAX test panel to see if you can route a sine wave from an output to an input on that board. You can do an analog output of a sine wave in your MAX test panel and route the output of that channel to an analog input channnel. Then run an analog input test panel at the same time and make sure you can see the sine wave. This issue sounds like something that you are going to have to troubleshoot through to find exactly where the problem lies. 


Chris N White

High Speed Products Group

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Message 4 of 5

Hi Chris,


        Thank you very much. I wil definately test it using the panels and i will let you know how it goes.

Thank you once again.



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Message 5 of 5