User:Pranav Rathi/Notebook/OT/2011/06/21/Noise issue with the optical tweezers

This page is dedicated to the different noise issues we experience during the data acquisition. I might decorate and elaborate this page very well but for now I am concentrating on the more important issue being faced right now. I am experiencing a weird oscillation in the data plane while acquiring the data. I mean by data plane is the plane in which the data is acquired. Some preliminary information about the oscillations:
 * Oscillations are more prominent during the DOG scan over the DOG profile.
 * Oscillations in X-signal are not continuous, they come and go.
 * Oscillations in y-signal are also like that.
 * But oscillations in the sum signal look continuous.
 * According to my observations two or more oscillations exists; 60~70 Hz and 120 Hz.
 * I do not know the amplitude yet.
 * The prime suspects are x-Piezo, QPD(x and y channel interference); environmental acoustic noise/unidentified noise object (UNO, DAQ cross talk. This list might increase.

June/21/2011
The investigation is under progress.

June/22/2011

 * There are two different oscillations exist. One is around 60Hz, and these are due to on-track (amplifier and controller of QPD). This oscillation is on-track gain dependent and never goes away even when the QPD is not connected to on-track. These oscillations can be controlled by manipulating the ground of the on-track power supply. I designed a weird circuit to do that and it is successfully controlling the noise.


 * 120 Hz is the oscillation exists. This oscillation is not continuous like 60Hz. It comes and goes. I am not surprised that this oscillation is piezo damping dependent. I compared sets of data, between piezo is damped and not damped. I found some difference and looking more into it.........

June/23/2011
The 60Hz periodic oscillations are due to the power supply came with on-track. The power supply does not have ground enforced polarity and maybe it is a half-wave rectifier (I am not positive on that). I tried different power supplies with the same result. The ground manipulation on on-track power supply worked but I was not satisfied. So I used a different power supply model: TR2V1000N00 with regulated +12V DC at 300mA. This power supply gives a regulated voltage with ground. If I use this power supply without the cancellation circuit, than it is no different. So I used a cancellation circuit in which I have a 300uF 200V capacitor in parallel to the output of the power supply and a ground which is directly connected to the common. The capacitor absorbs any fluctuation in the current and keeps the modulation at minimum, and any unwanted noise is grounded. Another possible noise source might be AC power-lines and shutter-powersupply situated close to the signal carrying wires. A comparison is shown below.



June/24/2011
I have also tested 12 V battery option. This option is little better overall noise wise. On-track needs 12V DC at 300mAmps. Any rechargeable-battery over 5 Ah can give 15 hours of constant power which is more than enough. Another exercise done today is isolation of the data acquisition hardware from various AC power lines. Data acquisition hardware includes, on-track, BNC wires, DAQ and QPD. I revised the whole electrical setup for tweezers, so now all the AC lines are far away from the acquisition hardware. This will definitely help in reducing the overall noise. On Monday I will verify it. Next Task on Monday: investigation of 120 Hz oscillations with nano drive piezo-alternate.

June/27/2011
60Hz noise issue is fully resolved now. The were two causes behind this noise. First x,y and sum signal BNC-wires were running close to the AC line and shutter-Powersupply. Power-supplies with transforms have 60Hz electromagnetic filed which might induce current into a conductor running close to it through electromagnetic induction. AC lines can do the same. Second the power supply for on-track was missing the ground.

I rearranged everything so the signal wires are isolated from any power-lines and power-supplies in vicinity. I changed the power-source for on-track to battery ( am using RYOBI cordless power drill's battery, which can supply power for hours to on-track, and we have two of them. We can use one when the spare is on charge). This solves the problem.

In case of 120Hz, i found that piezo might be the problem. I compared few sets of data between piezo dumped and not dumped. I found that when piezo is dumber the oscillation are weaker in magnitude. I am looking more into it, but if this is the case than i doubt it that this can be solved without changing the piezo stage.