>But if want to be certain that the opamp is working inside the manufacturers guaranteed output >voltage range you need to either reduce output voltage swing to say >0-2V (loss of 1 bit of measurement resolution) or increase the +ve >supply voltage or further change the circuit Hello Mr. Russell, Thanks for your mail. Increase the + ve supply voltage alone? Did you mean that I can increase the voltage swing by increasing the +5V to +7V or greater? All ORP probes and monitors operate over a range of +2V to -2V. I chose this amplifiers over other options such as LM356. What are the factors that I should consider while choosing an opamp? As Mr.Olin had suggested, when I set the gain of the opamp using a pot for a pre determined offset voltage, the error should be corrected by storing the offset values in the EEPROM? In future, if I am interested to check the calibration of the probe, should I write a code that find the offset and stores it in EEPROM? Yours Sincerely, Sairam ________________________________ From: Russell McMahon To: Microcontroller discussion list - Public. Sent: Thu, May 13, 2010 9:18:45 AM Subject: Re: [EE] Opamp design doubt > http://mechatronicscraze.wordpress.com/pic-orp/ > > I am currently experimenting what Mr.Olin had suggested on the calibration part. If you do not also address the fact that you are operating the op-amp outside it's guaranteed output voltage range it may cause you problems in future. The fact that the circuit appears to be operating correctly at present is 'lucky' at best. If this is a 'one-off' and you are happy to fiddle with it to make it work and to never be certain that it is working correctly, then using the opamp as is may be acceptable to you. But if want to be certain that the opamp is working inside the manufacturers guaranteed output voltage range you need to either reduce output voltage swing to say 0-2V (loss of 1 bit of measurement resolution) or increase the +ve supply voltage or further change the circuit. Russell -- 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