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A 10-channel in-flight calibrator recently developed by the National Bureau of Standards utilizes a unique system of cam-operated switches that eliminates many of the difficulties encountered in calibrators of comparable size and scope. Designed to identify telemetered information from a guided missile in flight, the device is compact and durable and particularly suited to telemetering applications in aircraft, missiles, or projectiles. The initial model, which was designed by L. L. Parker and W. A. Hereth of the NBS guided missiles laboratory, is now being manufactured by the J. P. Seeburg Company.
Telemetering involves the measurement of one or more quantities by electrical instruments, the transmission of the data to a distant receiving station, and the receipt and recording of the measured quantities. The information is usually transmitted by radio, although under some circumstances it may be carried by wire. The transmitted signals may be derived from transducers or pickups which translate mechanical movement into electrical impulses or they may be derived through direct coupling to electrical circuits. Normally, the information is then used to modulate a high-frequency radio carrier.
At the receiver-recorder it is virtually impossible to assign any finite value to the received information until two or more reference levels of modulation have been established in terms of the response of the receiving equipment. The NBS in-flight calibrator sequentially supplies each intelligence channel with four known levels of modulation. Thus, the telemetering record is provided with known reference levels of modulation from which the received data may be interpreted.
Transmission control of the calibrating signal, as well as the "data" signal, is achieved through the action of tWO groups of noise-free switches involving 40 separate switching operations. The first group contains 10 single-pole double-throw switches operated in sequence by a motordriven cam. Its function is to interrupt briefly and periodically the normal channeling of the operating information to the r-f. transmitter and to connect the calibrating circuit to the output, instead.
The second switching-group contains four single-pole single-throw switches, also operated by a motor-driven cam. The function of this group is to pass step-calibrating signals sequentially to the transmitter during the interval in which a particular telemetering channel is interrupted by the first group of switches. The step-calibrating cam cycles 10 times (four modulating signals with each cycle) for each cycle of the channel-interrupting cam; each interrupted channel receives identical calibrating signals.
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