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I did not wade through your code to see if I could spot a problem, but I may be able to help you understand better what is going on. I will put comments in your posting. At 05:35 PM 11/13/00, you wrote: >I have two sine waves (@2Khz & ranging from 0-1 Volt Amplitude) going >into the Primary and Secondary inputs of the C31. My program below is >supposed to measure a position ratio between the two voltages and the >result will range from 0 to 1 (0 corresponds to the case when the two >signals overlap each other and 1 to the case where they are furthest >apart) using the following formula: > Ratio=(Va-Vb)/(Va+Vb). Va and Vb are first converted to >DC by means of the following formula: > > Va=Sqrt[(2/N)*sum(data(n)^2)-2avg^2], where N is # of samples. I am not clear about what these equations mean. It looks like you are taking some sort of least squares calculation. Then you use that to determine the "ratio" of overlap. Is this a way to find the phase of the two signals? In any case, this will only work well if the two AC signal components have the same range or max value. If you want to compare them, you first have to scale them to similar ranges. >The program is first reading the input from the primary channel and >storing a 100 samples into a buffer then uses the formula above to >calculate the DC voltage. Then it reads the input from Auxiliary >channel and stores 100 samples in the same buffer and does the same >calculation. Finally, it uses the Ratio formula to calculate the >output. The resulting value is then outputted throug the C31 output. >However, since the resulting number is less than one.. it is first >scaled beofore it is outputted. The problem i am having comes here: I >can scale it by up to 300 and it gives me no more than 60 mV out! if i >keep increasing the scaling factore I get the same number. I need to >scale it to a bigger output (about 3 Volts) so I can get a better >reading and thus a better accuracy. I don't see any mention of the ADC or DAC coponents or the analog scaling factors being used. The first thing I would check is to see what range of output from the DAC you can get. You may be looking at a problem with the hardware. So just write some simple code that outputs a sine wave at maximum range from the DAC. See what you get on the scope. Do you know how many bits of resolution the DAC has? This will affect your code too. Then once you have the DAC working the way you want, you can loop the input ADC to the output DAC in real time and apply a sine wave to the input and see it on the output. Your code can apply whatever scale factor is appropriate. But keep in mind that the ADC and DAC have limited dynamic ranges. >I dont understand how the C31 reads and outputs voltages. What i mean >is: how does it read 50 mV for example? does it read it as 50000 for >instance? Also, why weren't I able to output more than 60 mV? I would >really apprecaite the help since this is making me go crazy. This depends entirely on your hardware. The C31 does not have a built in ADC or DAC. Your board has these devices. What the C31 reads will depend on the analog scale factor, the ADC resolution and how the value is justified in the C31 32 bit word. Rick Collins Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design Arius http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX |