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HELP!!!!! STUDENT IN NEED

Hi everyone, I’m a student who's completely confused using labview. I've a project due in a couple of weeks and it's wrecking my head trying to figure it out. I've got most of it done, but i can't get the rest of it.
I have to modify the attached file to tell a function generator (HP 33120a) to perform a frequency sweep between 100 hz and 10khz with a 1 volt amplitude. The sweep duration has to be 10 seconds and the digital multimeter (hp 34401a) is to be programmed to perform 100 ac voltage measurements. The results are then to be converted into dB and displayed on the front panel as a waveform graph.
Any ideas?
Any sort of help at all would be great. It's a small but annoying part of a big project.
Cheers
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Message 1 of 5
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Well, there's a shipping example in LabVIEW 7 that does exactly what you need but giving it to you as a 6.1 file would probably give you too much. There's a couple of things that you need to do in your example. It's set right now for a single frequency. From a start freq, end freq, and step size, you need to calculate the input frequency in a loop. For example, starting at 100 hz and 100 hz increments, you would set the arb to 100, 200, 300, etc., until the max frequency is reached. LabVIEW has a both a while loop and a for loop. You can enclose your program with either. You also need to change your dmm dunction to read ac volts instead of dc. You don't need to use the dmm to measure frequency because the frequency would be calculated by the VI. Look on the Numeric>Logarthmic palette for a function that you can use to convert your RMS reading from the dmm into dB. Finally, you should use an XY graph to plot the frequency versus gain. The XY graph takes an x array (frequency) and a y array (gain) as inputs. The measured gain and the input frequency can be output from a while loop or for loop and be automatically built into an array. For a while loop, click on the output tunnel and select Enable Indexing. This is the default behavior of a for loop so if you use one of these, you don't have to do anything. I hope that's enough to get you started.
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Message 2 of 5
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Hi dennis,
Thanks for replying, it was a great help. With some alterations and additions i now have the attached file which doesn't work, would anybody be able to modify it or tell me how to. If your going to tell me how, just dumb down the explaination a bit, i'm not the sharpest knife in the drawer!
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Message 3 of 5
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You may need these too, i'm running V6.1.
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Message 4 of 5
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The first thing is that you're only taking a single voltage measurement and you don't really know at what frequiency the function gen is at. You do a configure sweep with the fg but I'm not sure the sweep is actually starting. Even if the fg is sweeping, there's no synchronization between the fg and the dmm so you can't do any correlation. Instead of configuring a sweep, have a loop with the set fg frequency and the read dmm inside. You want to increment the fg's frequency with each iteration of the loop. Then, you would want to plot the results with a XY Graph so that frequency would be on the x axis and amplitude on the Y. Look at the attached picture. It just uses a fixed array of frequencies to output and there are a lot of refinements that can be made but I hope you get the general idea.
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Message 5 of 5
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