MEASUREMENT OF PH AND SPECIFIC ION CONCENTRATION

摘要

MEASUREMENT OF pH AND SPECIFIC ION CONCENTRATION A microprocessor-controlled pH and ion concentration meter is disclosed with improved calibration and testing procedures. For calibration (standardization), the meter stores number pairs (pXa, Ea) , (pXb, Eb) 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 Ea1 by Ea2) can be used to update the others (e.g., Eb2 to Eb2) without remeasurement by applying the formula: Eb2 = Eb1 + (Ea2 - Ea1). The meter can be tested for excessive internal bias current by measuring the potential (V1) when the meter is connected to a circuit a known voltage (E1) of low impedance and the potential (V2) when the meter is connected to a circuit of the same voltage source (E1) but of known high impedance and having the meter compare (V2 - V1) to a preset limit value. The meter can be tested for low internal impedance by further measuring the potential (V4) when the meter is connected to a circuit of a second external voltage (E2) and the known high impedance (R1). The meter then calculates: (V4 - V2) and compares that value to preset limits based upon E1, E2 and R1. Such limits can be derived as (Zo) (E2-El) / (R1 + Zo) wherein Zo is the minimum acceptable internal impedance.