Dear All, I have a question regarding the calibration of probes. As the ORP probes age, they tend to lose their accuracy of reading due to the aging of probes. The ORP probe's accuracy is checked using solutions that have potentials in the range of +200mV, +400mV etc. Can I adjust the offset voltage using a precision trim pot to make small adjustments in the offset voltage? Should I make minor adjustments in my code for offsets in voltage? Yours Sincerely, Sairam ________________________________ From: Marcel Duchamp To: Microcontroller discussion list - Public. Sent: Tue, May 11, 2010 4:52:37 AM Subject: Re: [EE] Opamp design doubt On 5/10/2010 9:18 AM, Marcel Duchamp wrote: > You are very close to the answer. Try removing R9 - this will change > the gain of the input amp from +2 to +1. With an offset adjust value > around +1V, you should get what you are looking for. > > Why the change? You have an input voltage range of -2V to +2V ==> 4V > span. You want an output span of +4V to 0V ==> 4V span also. Thus, you > need a system gain of -1 which your second stage already has. Sairam, by now, you have seen several conflicting suggestions. I still stand by what I wrote. I knew of the common mode range versus power supply levels limitation but it was my impression that you were successful with using it with the ORP application. That may have been incorrect on my part. But if you were successful before using it then it should work here as well. It is something for you to look into to verify correct operation. The data sheet is quite clear about unity gain operation. There should be absolutely no problem with that. Removing R9 will indeed make the first stage function with a voltage gain of unity. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist