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| DIY Transformer for use with Bode Plots. |
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| mawyatt:
Here's an example from 2019 where we could have used these Closed Loop techniques. Please read through the entire thread to get an idea of what's involved, one of the more complex analog feedback systems we've encountered in our career. https://www.photomacrography.net/forum/viewtopic.php?f=25&t=40510&hilit=PIezo+Electric Note the positioning graph with 200nm (0.2um) total range in 8~10nm (yes nanometers!!) steps :) The technique developed to make these nanometer measurements is another interesting topic :-+ Having this Closed Loop capability back when developing this project would have certainly helped, we knew about the technique and had used such as early as <1990 but with dedicated HP equipment, and didn't consider a mid-level MSO for this in 2019. Best, |
| bicycleguy:
@mawyatt Very interesting posts. Slightly off topic as far as the bode response but you might find this pdf about the actuators that align the mirrors on the Jame Webb Space telescope interesting. Quoting from the first page: 'This linear actuator is capable of 10 nanometer position resolution over a range of 20 mm and can operate under cryogenic conditions' |
| mawyatt:
--- Quote from: bicycleguy on June 04, 2022, 05:06:31 pm ---@mawyatt Very interesting posts. Slightly off topic as far as the bode response but you might find this pdf about the actuators that align the mirrors on the Jame Webb Space telescope interesting. Quoting from the first page: 'This linear actuator is capable of 10 nanometer position resolution over a range of 20 mm and can operate under cryogenic conditions' --- End quote --- Thanks, that's a very interesting article and quite an amazing device. Figures 12 & 14 show very good linearity and amazing repeatability. Our efforts pale in comparison, but in defense we did this at home and within a few $K out of pocket. We've been asked at other places how one measures sub-micron position, and since we're the OP guess it's Ok to go a little "off topic". The technique utilized to measure position levels down to the nanometer region (and at home) employs optical alignment of a target. The target is a simple piece of quality print paper laser printed with a medium grey patch. Detailed observation of the paper under high magnification revels a totally random pattern of carbon black "dots" of laser powder (which is low temperature plastic impregneted carbon) and fused to the white paper under thermal and pressure, which give a medium grey appearance from afar. The paper is cut and glued to a glass microscope slide and the slide placed on the piezo electric positioned almost normal to the optical axis to be viewed. A rigid fixed custom lens/camera fixture is arranged to view the slide and focused with a high quality (Mitutoyo 20X) stable lens & assembly on the slide center. Because the slide is almost normal optical axis the area above and below the center will be out of focus and a band of in focus will show with the DoF of the lens assembly (usually a few microns, a little trig will show how wide the band will be). The piezo element is commanded over the measurement range and at each position an image is captured with the hi res camera (Nikon D850). This small movement causes the DoF band to move across the image as the target moves under the piezo electric actuator. After the images are captured, they are feed into a software stacking routine like Zerene. This is setup to attempt to align each image in-focus band to the first image in-focus band. The software uses high contrast areas like the white paper and random carbon black dots to use as alignment guides, and uses algorithms to define in-focus areas. These tiny random carbon black deposits fused onto the paper actually work better as alignment points than the usual alignment guides, and there's plenty of them!! The amount of movement the image requires to realign with the first image is the movement the target imposed and is recorded. This recorded data shows the relative image shift required by each image in the stacking routine and used to evaluate the piezo electric positioning when compared to the total range involved. All this is done at the image pixel level and this is then converted to actual physical movement by the pixel dimensions. This is a relatively complex task and takes time, but in the end can resolve target position movements in the nanometer region as shown......and it doesn't require an expensive lab, or complex expensive setup :-+ Anyway, hope some folks find this interesting. Best, |
| mawyatt:
Just for fun we just did an open loop gain/phase measurement with the popular TL-431 shunt regulator. The setup was with the SDS2104X+ and a DIY Isolation transformer, with the primary driven by a AWG and unterminated. The secondary was placed between the Cathode and Reference in the feedback loop. The TO-92 package was plugged into a Photo-Board with jumpers, so lots of parasitic capacitance and contact resistance. Also did an output impedance plot by driving the TL-431 Cathode with a signal thru a 1K resistor and plotting the response across the 1K resistor. The results are shown in dB K Ohms, so 0dB is 1000, -20 is 100, -40 is 10, -60 is 1 and -80dB is 0.1 ohms. #19 is the Bode Plot of the TL-431 Open Loop Response with bias at 10ma, with Data Sheet from UMW (actual device OEM). #17 is with TL-431 Output Impedance biased at 10ma, with Data Sheet plot from TI (UMW doesn't have a 10ma plot) #18 TL-431 Output Impedance biased at 100ma, with Data Sheet plot from UMW. Edit: Added another plot (#23) showing a TL-431 with a shunt 101.4nF ESR 1.72 ohm cheap ceramic load capacitor. This is in the "Forbidden Zone" as shown in the data sheet graph and the Open Loop Bode plots shows the Phase Margin as ~8 degrees at ~310KHz, or just on the verge of oscillations, and somewhat confirms the Data Sheet zone!! Best, Best, |
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