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Abstract

A microprocessor-controlled pH and ion concentration meter is disclosed with improved calibration and testing procedures. For calibration (standardization), the meter stores number pairs (pX.sub.a, E.sub.a), (pX.sup.b, E.sub.b) where the pX values may be pH values (e.g., 4.00 and 7.00) and the E values are expressed in mV/deg K. When multiple standard values are stored, remeasuring one (e.g., replacing E.sub.a1 by E.sub.a2) can be used to update the others (e.g., E.sub.b1 to E.sub.b2) without remeasurement by applying the formula: E.sub.b2 =E.sub.b1 +(E.sub.a2 -E.sub.a1). Additionally, the meter can be tested for excessive internal bias current by measuring the potential (V1) when the meter is connected to a circuit of low impedance and the potential (V2) when the meter is connected to a circuit of the same voltage source but of known high impedance and having the meter compare (V2-V1) to a preset limit value.

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First Claim