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Need help

deski beri
Prodigy 30 points

Hello,

I am a chemistry student currently working on photoacoustic spectroscopy (frankly speaking; working to build a photoacoustic spectrometer). In my experiment, I am using IIIb series 633 nm HeNe laser, 25 mW , bombarded to malachite green sample in stainless steel compartment, I used a piezoelectric tranducer as a detector to sensorize heat generation by the sample. I have some problem to amplify signal or precisely voltage amplification. Do you guys have ideas how to amplify voltage generation from piezoelectric tranducer to be ready to displayed in the osciloscope. Fyi; from piezoelectric tranducer i notice the output votage as in range 88 mV - 235 mV by multimeter ( I am not quite sure whether this readable data is certainly could be believed or not since some power amplifier was not working to amplify this).

thank you

Deski

  • 0
    Genius 5430 points

    Deski;

    I do not see where you have a problem-- if your output signal is large enough to measure with a multimeter, you should be able to see it on a scope. ????????

     

  • 0 in reply to Neil Albaugh
    Prodigy 30 points

    Dear Mr. Albaugh

    I think it's not going to be a problem as well, but after my detector was plug in to the scope, I can see only noises, very much noises..there was no signal at all. In my opinion, signal and noise were overlaped in the similar mode, therefore I cannot distinguishes between signal and noises. By using a multimeter, it will displaying voltage in mV range whether it comes from signal or noises. After reading carefully some opinions in this forum, I got some point about my piezoelectric, it has properties as an eletric capasitor, so It will save some charges before recharging, I guess noises dominantly comes from that. From literatures- I found that my signal should be less than 100mV, since my sample after bombarded by laser will emit heat in 10 exp - 6 to 10 exp -5 degree centigrade range ( This is semiempirical datas by some scientists). When this heat directly convert to voltage in piezoelectric it must be defeated by the noise which comes from internal piezo capasitive properties. I am really sorry if this question is very basic since I have a little knowledge in electronics and now I am improving my electronic skills and knowledges.

  • 0 in reply to deski beri
    Genius 5430 points

    Deski;

    Your problem may be with your scope-- it may be unsuitable for what you are trying to observe.

    To see a signal from a piezoelectric sensor, the input impedance of the instrument must be very high. Check to see if your scope is a 1 megohm input; some scopes are only 50 ohms. Another thing to check is its bandwidth; you want no more bandwidth than is required by your input signal-- excess bandwidth only contributes noise.

    See if you can find one of the old Tektronix analog scopes such as a 7904 with a 7A22 plug-in. This scope has a sensitivity of 10uV/cm and the BW is selectable. You should easily see anything that you can see with a multimeter. Digital scopes tend to emphasize speed but generally have poor sensitivity and high noise; sometimes it helps to have a good old analog scope in the lab. They are available on the surplus market at bargain prices these days.

  • 0 in reply to Neil Albaugh
    Prodigy 30 points

    Thank you Mr. Albaugh, I'll consider your advice to replace my scope. Fyi; currently I am using Tektronix TDS 1002B. We have some old CRT scopes, probably this type will sufficient to my need. Thank you for  helping me a lot.