Abstract :
This paper is principally concerned with the direct-reading, continuous service pH-meter. Essentially a stable d.c. amplifier, its design is largely governed by the complex and inconvenient character of the electrode signal, and by the need for absolute rather than proportional accuracy; these factors are discussed in some detail. A quantitative analysis of the major causes of electrical error is followed by sections on automatic temperature compensation, direct-coupled amplifiers, and frequency conversion amplifiers, together with a note on the application of solid state devices. Two typical though widely different commercial instruments are described.
