Abstract: The circuit shows how to use the very high-input impedance of a MAX406 CMOS op amp to buffer the extremely high-output impedance of a pH probe. The advantage gained is the use of a standard low-cost cable instead of a high-cost Teflon dielectric coax cable. Battery drain is so low that the circuit can be continuously powered for thousands of hours on a single lithium cell. Use of a MAX130A integrating ADC is shown for driving a LCD display. The application note you have requested is available in Acrobat PDF format: APPLICATION NOTE 34: Low-Power Op-Amp Reduces Cable Costs for pH Probe (PDF, 39kB) A free Acrobat PDF reader is available from: http://www.adobe.com/products/acrobat/readstep.html Related Parts   APP 34: Nov 21, 2000 MAX130 3 1/2 Digit ADC with Bandgap Reference Full Data Sheet (PDF, 10.2MB) Free Samples MAX406 Single, Dual, Quad, 1.2µA Max, Single-Supply Op Amps Full Data Sheet (PDF, 7.4MB) Free Samples Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™. We Want Your Feedback!   Download, PDF Format (39kB)  AN34, AN 34, APP34, Appnote34, Appnote 34