Why do we need to zero the AF7000? How often should this be done?
One zeroes an AF7000 (SCM) in order to set the instrument at the ideal coagulant dosing. A SCM cannot tell an operator what their ideal dosing is (this must be determined by a jar test, or zeta potential meter), but it can tell an operator when the process is deviating from that ideal set-point if the instrument is zeroed on it. Zeroing should be done after every jar test or zeta potential measurement (this determines the ideal dosing, then the process is set to this dosing, then the instrument is zeroed), after a high-turbidity event post subsequent jar test, and if the instrument is seen to be drifting.