At 09:36 AM 5/3/00 +0200, Stephan wrote: >Regardless you will need a special probe for very long life as the junction >tends to clog up with protiens (common in the tank). This can be cleaned by soaking in 10% HCl/methanol. >pre-amplified probe or you have to provide a FET input stage as the pH probe >has an impedance of about 10^9 Ohms ( yes 1000 MOhms). This seems high. Maybe 100 MOhm. You can read a voltage with a DMM (10 Mohm input). ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================