Cause of Delay

Discussion in 'General Electronics Chat' started by Roma Kolevatov, Jul 23, 2018.

  1. Roma Kolevatov

    Thread Starter New Member

    Jun 26, 2018
    8
    0
    Good evening!

    Need help. Can't understand why the circuit doesn't work properly. (Please find pdf in attachments)

    Brief circuit description:
    Op-amps:
    OA1 -- output voltage is the same as input = V. AO2 -- output voltage is the same as input = V. AO3 -- inverting amplifier: output voltage is --V. Тherefore, voltage drop between outputs of OA2 and OA3 is 2V. Purpose of other amplifiers is to measure voltage drop on R6. OA4 and OA5 send voltage drop on R6 to inputs of differential amplifier OA6 without change. And at the output of A06 we have (voltage drop on R6)*R10/R8.

    Problem:
    When I connect the circuit to voltage generator (sinus signal), I see nothing at the output of circuit (straight line). After waiting for ~15 min, sinus appears at the output. However, it is not a ''pure'' sinus, but sum of main signal plus some high-frequency sinus.

    Question:
    What is the cause of this delay? Where does the extra high-frequency sine come from? Any ideas?

    Thank you!
     
  2. Xavier Pacheco Paulino

    Active Member

    Oct 21, 2015
    647
    68
    Why do you say AO3 output voltage is --V? According to your circuit, AO3 is an AC Op-amp Integrator with DC Gain Control, which produces a more complex output. As far as I concerned, the output signal is very dependent on time.
     
  3. Roma Kolevatov

    Thread Starter New Member

    Jun 26, 2018
    8
    0
    I think that AO3 is inverting amplifier: V_out=-R4/R3V_in. Note that the capacitor is in parallel to resistor, I connected this capacitor to reduce noises, it's recommended according to data sheet, but it's not compulsory. Current almost doesn't go through this capacitor. The same holds for the capacitor in the last differential amplifier, AO6.

    By the way, I tried to disconnect all the capacitors -- nothing changes.
     
  4. Veracohr

    Distinguished Member

    Jan 3, 2011
    674
    101
    What are the supply voltages & does the input have a DC offset?
     
  5. Roma Kolevatov

    Thread Starter New Member

    Jun 26, 2018
    8
    0
    1) 10V for each op-amp
    2) input does NOT have DC offset
     
  6. Veracohr

    Distinguished Member

    Jan 3, 2011
    674
    101
    If your 10V supply is +/-5V and the input is centered on 0V, then I don't see a problem with the circuit. Recheck the connections and pinout of the opamps.
     
    Roma Kolevatov likes this.
  7. Glenn Holland

    Active Member

    Dec 26, 2014
    628
    317
    The title of your post is "Cause Of Delay".

    Are you talking about bad weather delaying an airline flight or an electronic problem??? :p
     
    Roma Kolevatov likes this.
  8. Roma Kolevatov

    Thread Starter New Member

    Jun 26, 2018
    8
    0
    I am not very good in English. How is it best to say?
     
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