A computer-controlled tension monitoring system for drift chamber wires

We describe a wire tension monitor used in the construction and operation of a large drift chamber. This system monitored the tensions of up to 64 wires by locating their resonant frequencies using a sinusoidal current in a weak magnetic field. Wires of 20 mu m tungsten and 100 mu m aluminum whose lengths varied from 7 to 70 cm were monitored, with resonant frequencies ranging from 160 to 1850 Hz. A multiplexing scheme was implemented which dwelled on each wire for about half a minute. This monitor combined custom electronics with a commercial I/O board and a PC/286 computer. The short-term reproducibility (sigma) of the measurements was +/- 0.05 g (+/- 0.1%) for tungsten wires and 1.1 g (+/- 1.0%) for aluminum wires. Limitations of the method are discussed.