Industrial Electronic Control [antikvár]

INTRODUCTION When anyone not familiar with electronic control first encounters vacuum-tube or thyratron symbols on wiring diagrams or attempts to analyze the strange-looking components on the back of a typical electronic panel, it is small wonder that he becomes somewhat confused and is inclined to feel that electronic control is something far beyond the grasp of the average serviceman, electrical engineer, or electrician. On better acquaintance, however, this strangeness begins to disappear. Yes, those ceramic tubes are resistors, although somewhat smaller in size than those he has been used to. The varicolored bakelite rods are also resistors, dissipating a watt or so but having a resistance of perhaps a number of megohms. The colors constitute a simple and efficient color code of resistance value and tolerance. The small wax-filled cardboard and metal cans are capacitors (or, as we used to call them, "condensers") similar to those now in common use for spark and radio interference protection, for motor starting and phase splitting, and for power-factor correction. Sometimes the smallest capacitors appear as bakelite blocks coded by colored dots or bands, as are the resistors. Transformers and reactors appear in their old familiar roles and should cause no confusion. Sometimes a reactor and a capacitor are combined to produce a resonant element to present maximum or minimum impedance, or a reactance and a resistance may be combined to produce a phase shift, but both these phenomena are standard a-c engineering and not peculiar to electronic control. Electron Tubes. Those essential and so often misunderstood elements, the electron tubes themselves, are fundamentally among the simplest of electrical devices. This statement is worth re-