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In the production of textile yarns, the speeds of the processing machinery are extremely important. Constant speed assures uniform quality and fewer defects in the cloth woven from the yarn, while the maintenance of rated speeds is necessary for efficient production.

The stroboscopic method of speed measurement is widely used in textile plants, because there is no mechanical contact between machine and tachometer, so that tha speed of the machine is not affected. In spinning and twisting operations, a complete frame of spindles can be checked quickly for proper speed and, at the same time, defects in the operation of the machine can be spotted by means of the slow-motion effect.

This photograph shows the General Radio Strobotac® being used to measure the speeds of spindles on an Atwood twister and to observe the shape of the yarn balloons.

Figure 2. Panel view of the amplifier.

Supply, whose output necessarily limits the maximum output power of the amplifier and the choice of tube types. Of the available tube types that could be operated from the power supply, a pair of triode-connected 6WG-GT's gave the best results.

A 12AX7 miniature twin triode is used in the input stage and phase inverter since it combines the economy of a single envelope with the desirable features of high gain and low cathode-heater power. It will be noted from Figure 3 that the phase-inverter plate supply is taken from B+ through a resistor to enable this stage to handle larger signals. A capacitor connects the phase-inverter plate resistor to the output, so that for a-c signals the circuit is equivalent to that of Figure 1. The

Figure 3. Complete circuit diagram.

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