{"action":"created","issue":{"url":"https://api.github.com/repos/WuMRC/drive/issues/21","labels_url":"https://api.github.com/repos/WuMRC/drive/issues/21/labels{/name}","comments_url":"https://api.github.com/repos/WuMRC/drive/issues/21/comments","events_url":"https://api.github.com/repos/WuMRC/drive/issues/21/events","html_url":"https://github.com/WuMRC/drive/issues/21","id":58077325,"number":21,"title":"Calibration Issue","user":{"login":"tunjid","id":8147224,"avatar_url":"https://avatars.githubusercontent.com/u/8147224?v=3","gravatar_id":"","url":"https://api.github.com/users/tunjid","html_url":"https://github.com/tunjid","followers_url":"https://api.github.com/users/tunjid/followers","following_url":"https://api.github.com/users/tunjid/following{/other_user}","gists_url":"https://api.github.com/users/tunjid/gists{/gist_id}","starred_url":"https://api.github.com/users/tunjid/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/tunjid/subscriptions","organizations_url":"https://api.github.com/users/tunjid/orgs","repos_url":"https://api.github.com/users/tunjid/repos","events_url":"https://api.github.com/users/tunjid/events{/privacy}","received_events_url":"https://api.github.com/users/tunjid/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":2,"created_at":"2015-02-18T14:52:06Z","updated_at":"2015-02-19T14:58:27Z","closed_at":null,"body":"While the calibration sketch works as it should, there's the issue of not knowing exactly what resistor combination is engaged from the digital rheostats r1 and r2 at any one time.\r\n\r\nThe ideal case with each wiper position increasing linearly does not correspond with measured values from a multimeter or the LCR. The LCR at a fixed frequency (20 Hz) was then used to create a lookup table for each step for both rheostats. The Lookup tables are in the \"Text Files\" folder under Analysis/MATLAB. The data generated with this lookup tables is in the same folder with the name \"Test\".\r\n\r\nAfter a brief test run, The values computed using the lookup table in the ideal model does not correspond to measured data by the AD5933. This is in contrast to previous tests with discrete r1, r2 and capacitor values measured by a multimeter.\r\n\r\nI currently have two reasons this may be:\r\n\r\n1. The lookup table generated from the LCR at 20 Hz is bad, and does not match the actual values from the rheostats.\r\n\r\n2. As Il Taek mentioned in a previous issue, the AD5933 has to be used in Range 4 so the current injected is below 5 mA. This is because the rheostats are rated to an absolute maximum of 5 mA flowing through it continuously. Range 4 has an output impedance of about 600 Ohms, which is 3 times higher than Range 1 (The range used prior) whose output impedance is 200 Ohms. This should lead to a higher rate of accumulated errors as Il Taek pointed out.\r\n\r\nThe case may even be a combination of both reasons. As of right now, it needs to be ascertained what exactly the issue is before calibration can continue. My current plan is to somehow interface the LCR with the rheostats the same way I currently have the AD5933 and measure the rheostat values both with the LCR and AD5933.\r\n\r\nThe biggest challenge here is the software that can control both the LCR through the GPIB interface while simultaneously controlling the rheostats via i2c. LabView and Visual Basic are the current choices I have been able to narrow down so far, with my preference leaning towards Visual Basic.\r\n\r\nSuggestions are very much welcome."},"comment":{"url":"https://api.github.com/repos/WuMRC/drive/issues/comments/75065348","html_url":"https://github.com/WuMRC/drive/issues/21#issuecomment-75065348","issue_url":"https://api.github.com/repos/WuMRC/drive/issues/21","id":75065348,"user":{"login":"tunjid","id":8147224,"avatar_url":"https://avatars.githubusercontent.com/u/8147224?v=3","gravatar_id":"","url":"https://api.github.com/users/tunjid","html_url":"https://github.com/tunjid","followers_url":"https://api.github.com/users/tunjid/followers","following_url":"https://api.github.com/users/tunjid/following{/other_user}","gists_url":"https://api.github.com/users/tunjid/gists{/gist_id}","starred_url":"https://api.github.com/users/tunjid/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/tunjid/subscriptions","organizations_url":"https://api.github.com/users/tunjid/orgs","repos_url":"https://api.github.com/users/tunjid/repos","events_url":"https://api.github.com/users/tunjid/events{/privacy}","received_events_url":"https://api.github.com/users/tunjid/received_events","type":"User","site_admin":false},"created_at":"2015-02-19T14:58:27Z","updated_at":"2015-02-19T14:58:27Z","body":"Hi Il Taek,\r\n\r\nI have used the LCR with generic resistors and it at single frequencies and it works fine, the base line I'm comparing it to here is a standard digital multimeter. The issues I've had with the LCR occur at frequency sweeps, especially around 10 KHz that suggest it needs to be recalibrated.\r\n\r\nThe issue I have now is while the digipot works fine, I don't know the actual resistance for each discrete step so I can't actually compare values measured by the AD5933 to a theoretical model, talk less of the LCR. \r\n\r\nThe issue basically boils down to this, how do we create a very accurate lookup table for all 64 steps in both digitpots used in the experiment quickly? "}}