Electronically balanced recorder for flight testing and spectroscopy

A multiple-point potentiometer recorder for thermocouples is described having a slidewire driven to balance by a small induction motor powered from a 6L6 electron tube. The preamplifier gain is sufficient that the conventional input transformer (voltage step-up type) is not required, and thus a high impedance input circuit is made available. This permits the use of small capacitance values in the RC circuits for signal filtering and motor damping. The relation of this to the short balancing time (1.5 seconds) is discussed. Spectroscopy supplied the incentive for the development of two additional but similar recorders. The first of these is a curve-drawing multiple-range microampere recorder with the smallest range 0.5 micro-ampere, and with a balancing time of less than 1.0 second. The second is a multiple-range current-ratio recorder requiring only about 10 microamperes for the reference current.