Functions of Motor Control:Selector Switches

Selector Switches

Selector switches are operated by turning a knob instead of pushing a button. A very common selector switch is the MAN-OFF-AUTO switch. MAN stands for Manual and AUTO stands for Automatic. This is

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a single-pole double-throw switch with a center off position, as shown in Figure 2 – 29. When the switch is in the OFF position, as shown in Figure 2 – 29A, neither indicator lamp is turned on. If the switch is moved to the MAN position, as shown in Figure 2 – 29B the red lamp is turned on. If the switch is set in the AUTO position, Figure 2 – 29C, the green lamp is turned on. Another symbol often used to represent this type of switch is shown in Figure 2 – 30. A combination START-STOP push-button station, pilot lamp, and HAND-OFF-AUTO switch is shown in Figure 2 – 31.

Selector switches often contain multiple contacts and multiple poles (Figure 2 – 32). A symbol used to represent a selector switch with three poles, each having three terminals, is shown in Figure 2 – 33. This selector

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switch contains a common terminal for each of the three poles. The common terminal is connected to the movable contact. A different type of selector switch is shown in Figure 2 – 34. Switches of this type are often supplied with a chart or truth table indicating connections between contacts when the switch is set in different positions. In this example, there is no connec- tion between any of the contacts when the switch is set in the OFF position. When the switch is set in position A there is connection between contacts 3 and 4, and 5 and 6. When the switch is set in position B there is connection between contacts 1 and 2, 5 and 6, and 7 and 8. It is not uncommon to see a combination of selector switches, push buttons, and meters mounted on a single control panel (Figure 2 – 35).

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Ahmed Farahat is EECS engineer With 18 years of experience in the field he worked on different technological discipline and and had honored Post Graduate Diploma In Computer Science And Engineering

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