Pulse code modulation telemetry in ski injury research. I. Instrumentation.

Measurement problems can be classified into instrumentation, data transmission and recording, and analysis. This paper focuses on the transmission of multichannel, high-volume, high-frequency, high-accuracy data. Boot-ski dynamometer and skier velocity anemometer data provide 13 channels of max. 8-mV signals requiring 8-microvolt resolution or 4.45-Newton dynamometer resolution. The data transmission system features durability, power consumption approx. 10 Watts, weight 4.54 kp, range greater than 3,500 m, frequency response 250 Hz, accuracy 1 per cent, temperature stability, dynamic range plus or minus 2 inches. The transducer signals are ampflified to plus or minus 10 V for the 100-kbps PCM system. Special AC amplifiers, driven by an amplitude-stabilized power oscillator, were designed for elimination of radio frequency interference (RFI), improved stability and high signal/noise. Sixteen words are sequentially sampled at 521/sec-13 data, 2 frame counters, and 1 sync. The ground station consists of the PCM decoder with real-time capability and an analog tape recorder. Data is subsequently buffered and formatted onto digital tape by mini-computer.