Lab 6

More documents

Recommendations

Info

5. Repeat for gains of 5 and 6. 6. Download and open the file AnalyzeTachoData.vi from the course website. Input the sample period for your data the dt control. If you’re not sure what this is, you can open any of your .txt files and read the dt value in Excel. 7. Run this vi and open one of your data files. It will then ask you to input a name to save the data. The data saved is after the input data has been rectified and filtered. You will see two waveform graphs. The first one shows the data exactly as it was read in. The second one is the rectified and filtered data. 8. Experiment with the filter block in the VI. The default filter is a 3 rd -order butterworth filter with a 25 Hz cutoff frequency. Try adjusting cutoff frequency to a lower and higher frequency. What do you observe? Next, try changing the filter order. Does this have any effect on your result? 9. Open the filtered data in Excel. Plot all three on the same graph, determine the 63% rise times and record the values in the table below. Make sure to label the axis and hand in the plots with your lab write up. C. Create a VI to make steady-state measurements of current & motor speed vs voltage In this part of the lab you will write a VI based on the VI from Lab 2 (lab2.vi) to automatically measure the steady-state speed and input current of the motor as the input voltage is increased. This time, instead of graphing the results you will store the RMS tachometer voltage and the mean input current to a file for later analysis. 1. Open your VI from Lab 2 or use the file downloaded from the class web site. Save it under a new file name. A picture of the changes that you will make to the block diagram is shown in Figure 3. input voltage Figure 3: Wiring the DAQ Assistant to the Write LVM File VI. 2. Go to the block diagram and delete the XY graph, the Build XY Graph and the two To DDT vi’s. In their place, create a block to store the data to a Labview measurement (LVM) file. Go to Functions»Output and place a Write LVM block outside the While Loop. Select Save to one file and check Ask user to choose file. Under X Values Column select One Column Only. Leave the default settings for all the other values. 12
3. Place a Merge Signals block next to the data input on the Write LVM from Functions»Signal Manipulation. Use the mouse to resize the block to give it three inputs. This will allow you to store three columns of data in the file (the input voltage, the mean current input, and the RMS tachometer reading). 4. Change the Time Delay in the second frame of the stacked sequence. Use a delay that is at least 3τ so that the motor will have reached a steady speed before you make any measurements. 5. Modify the DAQ Assistant Express VI in the third sequence frame to measure 250 samples of the tachometer and current sensor outputs. To do this, make the following configurations in the DAQ Assistant configuration wizard: • In addition to measuring the voltage on ai0 (ACH0), add a new voltage measurement to measure ai1 (ACH1). • In the Task Timing section, select N Samples. • Set the Samples to Read to 250, and set the sample rate to 5000 samples/sec. 6. The DAQ Assistant you created will produce 250 samples per channel with each iteration. We will first convert the data into two arrays with 250 samples each. Go back to the block diagram, right click and select Functions»Signal Manipulation and choose From DDT. Place this in the while loop and select 2D array of scalars – columns are channels then click ok. Wire the output of the DAQ Assistant to the input of the From DDT. Add an Index Array block and split the 2D array into two 1D columns as was done in Lab 3. 7. We will store only the RMS value of the tachometer output and the mean value of the current sensor output. Right click and select the RMS block from the menu: Functions»All Functions»Analyze»Mathematics»Prob and Stat. Place this in the while loop and wire the first data array (from ACH0) to the RMS block. Repeat the process to create a Mean block and wire it to the second data array (from ACH1). 8. Wire the output voltage (which used to be connected to the X-axis of the XY graph) to the top terminal on the Merge Signals block. Wire the output of the Mean block and the RMS block to the border of the While loop. Right click on the two new loop tunnels at the border of the While loop and select “Enable Indexing.” Wire these loop tunnels to the second and third inputs to the Merge Signals block. Labview will automatically create To DDT blocks to convert the signals to Dynamic Data Type. 9. Save your completed VI. Testing 1. Make the following front panel settings of the VI: Vmin = 1.5 V, Vmax = 3.25 V, Nsteps = 7. 2. Press the Run key. When your program is complete, you will be prompted to save your data to a file. 3. Open the file with Excel and check the data. Your current sensor and tachometer readings at Vin = 0.4V, 0.5V and 0.6V should agree with the steady-state values from Part B. If they do not, there probably something wrong with your VI. Ask your TA for help. 13
Page 1: EME 107B - SPRING 2007 Week of May
Page 7 and 8: (end article from Howstuffworks.com
Page 9 and 10: Then we can find the motor torque b
Page 11: • Frequency (Hz): 0.5 c. Click on
Page 15: C. Measuring the Motor Steady State

Lab 6

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?