HP HP-Bench-Briefs-1973-07-08 free download

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VOLUME 13 NUMBER 3 JULY-AUGUST 1973 QUARTZ CRYSTAL at a constant temperature usually around 65OC regardless of the am- OSCILLATORS bient temperature outside the oven. Ovens are of two general types, on-off and proportional. by Marv Willrodt The on-off oven uses a snap action thermostat as a temperature sens- The accuracy of most Hewlett- ing element. The cost is low but performance is only moderate Packard counters and many other since the thermostat by nature has instruments is determined to a a temperature differential between great extent by the accuracy of the "on" condition and the "off' the mechanical vibrating fre- condition, thus the crystal temper- quency of a thin crystalline quartz ature is constantly being cycled plate used in the time base refer- by some small amount which ence oscillator. To make a quality quartz oscillator, a shows up as output frequency Since the quartz plate is vibrating source of pure quartz must be located. cycling. Wear and sticking of the mechanically, its frequency will be with ambient temperature change thermostat points can cause a influenced among other things by is much greater than for good oven gradual shift of oven temperature physical size, which can change as crystals. or even erratic operation. Also the quartz plate expands or con- arcing of the points can introduce tracts with temperature changes. Temperature effect can be reduced electrical noise into the oscillator by combining temperature com- output. All of these things are Several things are done to reduce pensating elements--temperature the magnitude of this frequency undesirable since they cause fre-