0

I was reading this potentiostat paper: (which was found here)

pot circuit

I was wondering how this I/V current to voltage converter works to the right. Correct me if I am wrong here.

I am pretty sure it goes like this:

Iwe flows in or out from the virtual GND of the C op-amp, but since no current flow there, it goes from the Rm (28.8MΩ), and creates a voltage difference there, which you can measure at Vout.

I wanted to confirm this so from the Table II, lets take the 26.6uA case:

table 2

The voltage across R8:

V=I*R => latex

766V is way larger from the 5V Op amp input.

Even if one looks at the graphs, lets take the 3*10^-5[A]:

Graph

latex

Again, a really large value.

I am starting to think that the values I find are in millivolts, or the author of the article used a smaller resistor and forgot to change its value on the PDF.

JRE
  • 67,678
  • 8
  • 104
  • 179
Christianidis Vasileios
  • 2,645
  • 2
  • 9
  • 32
  • 1
    I will bet those currents are nA. – Ed V Apr 01 '21 at 17:25
  • I cound not agree more, but it says **current(A)** and **x10^-5** – Christianidis Vasileios Apr 01 '21 at 17:27
  • 1
    Then that seems to leave the resistor being 28.8 k, so the schematic has an error. Given that the paper was published last year, maybe contact the corresponding author. – Ed V Apr 01 '21 at 17:41
  • 3
    Will the horror of units in square brackets ever end? – carloc Apr 01 '21 at 18:17
  • In my shitty university, they taught me that the units are placed in brackets. I found this very smart since you can distinguish them from variables. And yes I have seen people hating them. Why is it so? – Christianidis Vasileios Apr 01 '21 at 18:19
  • 2
    Here is the long form on correct usage: https://physics.nist.gov/cuu/pdf/sp811.pdf pages v and vi are an excellent summary. Here is another one, starting on document page 130: https://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf – AnalogKid Apr 01 '21 at 18:36
  • 1
    In short [*] means"units of *" and can, of course, be used, but in the right way. [Ic]=A is correct and means the the quantity Ic is measured in amperes.Ic [A] is nonsense instead. – carloc Apr 02 '21 at 00:07

1 Answers1

0

This resistor value was wrong after all. A resistor of lower value was needed to output something else rather than its maximum/minimum voltage.

With this larger resistor, the output was either +2.5V (maximum input voltage of the op amp) or -2.5V (the lower input voltage of the op amp.)

JRE
  • 67,678
  • 8
  • 104
  • 179
Christianidis Vasileios
  • 2,645
  • 2
  • 9
  • 32