A SIMPLE AND INEXPENSIVE VOLTAGE REGULATOR FOR LABORATORY USE

Abstract

Variations in voltage are frequently a source of trouble in experimental work resulting in unreliable data, injury to equipment, or shortened life of electrical devices. Considerable effort has been expended in attempts to solve this fundamental problem but no wholly successful regulator for all purposes has yet been developed due to the diversity of voltage requirements. Some devices require essentially instantaneous correction whereas others can tolerate appreciable lag, but must have no distortion of wave form. There are in general three types of voltage controls. Perhaps the best known and most commonly used of these is the electromagnetic type (no moving parts) in which a change in the flux of the field or some similar system is used so that the output voltage remains constant for great differences of input. This type has the definite advantage of being very rapid, usually correcting within one cycle, but has the disadvantage that it distorts the wave form. For this reason motors and other equipment affected by wave form and power factor function poorly or not at all. In addition, in order to get sufficient amperage supplying power, a relatively small (10 amp.) model must weigh about 75 lbs. For larger sizes, the weight is proportional. In some devices, such as photolometers, even these controls cause flares'' in the bulbs used and hence drifts of null. A second general type of voltage regulator is that obtained with a complicated circuit of radio tubes. They have voltage control in the general range of hundredths of a volt for outputs of 110 volts and are highly desirable for certain specific uses. They are very limited in application, however, and will not be described further. A third type of regulator is the fundamental one that has been used in the electrical industry since its inception. It consists essentially of a transformer with exposed windings so that a movable contact can pass across them and thus pick up any voltage desired. This general form is broadly used on rural power lines. They are automatically operated and are set to hold the voltage within certain limits. This type of control can be built with any capacity and almost any tolerance. It has the very great advantage of giving no wave distortions and of having a high efficiency. It has the very distinct disadvantage of time lag, for it takes from one to several seconds to correct line variations. Recently, in working with a recording potentiometer, voltage variations from 90 to 120 were encountered. An electromagnetic regulator of the sola type was available but the recorder would not function when this was used as voltage supply. The potentiometer has a small induction motor and several radio tubes. Thus it was im-