A possibility of simultaneous logarithmic-linear direct-current measurement

A description is given of a simple circuit for dc measurement in a range of several decades with simultaneously logarithmic and linear indications. Separate mathematical analyses are carried out for the cases of employing diodes and transistors as nonlinear elements. The obtained relations indicate the requirements imposed upon nonlinear elements and operational amplifiers to achieve a desired accuracy of measurements. Experimental results have shown that diodes permit covering of a measuring range of five linear decades whereas the transistors cover a measuring range of seven linear decades. The linearity was better than 0.15 percent per decade of variation of measured current. Temperature stability was better than 250 ppm/°C.