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I found this circuit from Encyclopedia of Electronic Circuits Volumes 1 by RUDOLF F. GRAF I used Multisim to simulate. When switches S1 and S2 are open (U1A@3 and U1B@6 are floating) and I measured by Oscilloscope (and probe) and found that the voltage are 6.6V. I got the following results after measuring by Oscilloscope:

U1A@3 = 6.6V, U1A@2=6.5V, U1B@5 = 5.5V, U1B@6 = 6.6V, U1A = 10.6V, U1B = 0V og U1C@10 = 5V U1C@9 = 2.6V, U1D12 = 10.1V, U1D@13 = 1.9V og U1D = 10.6V

I would like to know:

  1. Where are voltage on U1A@3 and U1B@6 (6.6V) from?
  2. C1 are drawn with wrong polarity?
  3. Why R10 and R7 not the same value?

Actually I really don't know about floating input and it seems that all the opamps are operating in Saturation.

  • \$\begingroup\$ Why don't you contact them and see what they say? Has your curiosity got some urgent need of an answer? \$\endgroup\$ – Andy aka Feb 1 '14 at 21:21

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