F fleamonkey New Member May 8, 2010 #1 hi could anyone tell me why i get a negative gain on this circuit please. i am quite new to op amps and cannot understand why i have not got 10 times gain Attachments Doc1 wheatstone.doc 31 KB · Views: 176
hi could anyone tell me why i get a negative gain on this circuit please. i am quite new to op amps and cannot understand why i have not got 10 times gain
Nigel Goodwin Super Moderator Most Helpful Member May 8, 2010 #2 You have the resistors the wrong way round (the 10K and 1K), so you've got a gain of 0.1 instead of 10. I would also suggest you post diagrams as GIF or PNG, and not as large DOC files which many people won't be able to view.
You have the resistors the wrong way round (the 10K and 1K), so you've got a gain of 0.1 instead of 10. I would also suggest you post diagrams as GIF or PNG, and not as large DOC files which many people won't be able to view.
Hero999 Banned May 8, 2010 #3 Yes, please use PNG. I also don't have MS Word, just the free viewer program which is a bit flaky. OpenOffice.org is good but some of the more complex Word documents don't display properly. I've converted it to PNG but it looks a bit distorted. What are you trying to do? It looks like you're trying to make an instrumentation amplifier. See the Wikipedia article for a schematic. Instrumentation amplifier - Wikipedia, the free encyclopedia Attachments monkey opamp1.png 6.1 KB · Views: 189 Last edited: May 8, 2010
Yes, please use PNG. I also don't have MS Word, just the free viewer program which is a bit flaky. OpenOffice.org is good but some of the more complex Word documents don't display properly. I've converted it to PNG but it looks a bit distorted. What are you trying to do? It looks like you're trying to make an instrumentation amplifier. See the Wikipedia article for a schematic. Instrumentation amplifier - Wikipedia, the free encyclopedia
Nigel Goodwin Super Moderator Most Helpful Member May 8, 2010 #4 Hero999 said: What are you trying to do? It looks like you're trying to make an instrumentation amplifier. Click to expand... Presumably you didn't read the name of his attached Word file?.
Hero999 said: What are you trying to do? It looks like you're trying to make an instrumentation amplifier. Click to expand... Presumably you didn't read the name of his attached Word file?.
Hero999 Banned May 8, 2010 #5 No I didn't. What's your point? I was right, an instrumentation amplifier is commonly used to monitor a Wheatstone bridge.
No I didn't. What's your point? I was right, an instrumentation amplifier is commonly used to monitor a Wheatstone bridge.
audioguru Well-Known Member Most Helpful Member May 8, 2010 #6 The lousy old 741 opamp has a minimum input resistance of only 300k ohms so it will severely mess up this circuit that has 1M ohm input resistors. Why is R11 only 0.001 ohms? It should be a piece of wire because the gain of the first two opamps is only 1.
The lousy old 741 opamp has a minimum input resistance of only 300k ohms so it will severely mess up this circuit that has 1M ohm input resistors. Why is R11 only 0.001 ohms? It should be a piece of wire because the gain of the first two opamps is only 1.
Nigel Goodwin Super Moderator Most Helpful Member May 9, 2010 #7 Hero999 said: No I didn't. What's your point? I was right, an instrumentation amplifier is commonly used to monitor a Wheatstone bridge. Click to expand... The point is the filename tells you EXACTLY what he's doing.
Hero999 said: No I didn't. What's your point? I was right, an instrumentation amplifier is commonly used to monitor a Wheatstone bridge. Click to expand... The point is the filename tells you EXACTLY what he's doing.
Hero999 Banned May 9, 2010 #8 audioguru said: The lousy old 741 opamp has a minimum input resistance of only 300k ohms so it will severely mess up this circuit that has 1M ohm input resistors.. Click to expand... There's no need for the input resistors which should be removed altogether. The bridge has an putput impedance of 14k which is then fine to drive 300k inputs.
audioguru said: The lousy old 741 opamp has a minimum input resistance of only 300k ohms so it will severely mess up this circuit that has 1M ohm input resistors.. Click to expand... There's no need for the input resistors which should be removed altogether. The bridge has an putput impedance of 14k which is then fine to drive 300k inputs.