This paper describes the combination of a PDP8 digital computer with a Trebel balancing machine to produce real-time presentation of trim weights and their positions.

First, the basic equations of motion are derived. These equations give trim moments and angles as functions of the force components measured by the force transducers. Experiments have shown that there is a considerable amount of noise present in these force components. It is therefore necessary to reduce this noise before the electrical output of the force transducers can be used in the basic equations of motion by the computer.

Two techniques are used for reducing the noise. A low-pass electrical filter reduces the high-frequency noise before the signal is transmitted to an analog-to-digital converter. After the signal is digitized and entered into the computer, a program based on a regression analysis reduces the effects of lower frequency aperiodic noise.

Approximations for the phase shift and attenuation due to the mechanical and electrical characteristics of the force transducer acting in conjunction with the impedance effects of the electrical filter are given. To obtain these approximations, the force transducer is described by a linear, second-order transfer function. Compensation for these effects is accomplished automatically by the computer program.

Operation of the system to date has indicated improved accuracy and significant time savings.