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Where a switch contains both normally open (NO) and normally closed (NC) contacts, the order in which they make and break may be significant. In most cases, the rule is break-before-make or B-B-M; that is, the NO and NC contacts are never simultaneously closed during the transition between states.
Each key of a computer keyboard, for example, is a normally-open "push-to-make" switch. A "push-to-break" (or normally-closed or NC) switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released. An example of a push-to-break switch is a button used to release a door held closed by an electromagnet.
A push switch (button) is a momentary or non-latching switch which causes a temporary change in the state of an electrical circuit only while the switch is physically actuated. An automatic mechanism (i.e. a spring ) returns the switch to its default position immediately afterwards, restoring the initial circuit condition.
Time-delay relay contacts must be specified not only as either normally open or normally closed, but whether the delay operates in the direction of closing or in the direction of opening. The following is a description of the four basic types of time-delay relay contacts. First, we have the normally open, timed-closed (NOTC) contact.
The contacts are usually normally open, closing when a magnetic field is present, or they may be normally closed and open when a magnetic field is applied. The switch may be actuated by an electromagnetic coil, making a reed relay, [2] or by bringing a permanent magnet near it. When the magnetic field is removed, the contacts in the reed switch ...
The transistor can be operated as a switch. The bipolar junction transistor (BJT) cutoff and saturation regions of operation can respectively be treated as a closed and open switch. The most widely used electronic switch in digital circuits is the metal–oxide–semiconductor field-effect transistor (MOSFET). [2]
Figure 1D illustrates a double-pole, double throw (DPDT) switch. Contact form, or simply form, is the term relay manufacturers use to describe a relay's contact configuration. "Form A” refers to a single-pole, normally open switch. "Form B" indicates a single-pole, normally closed switch, and "Form C" indicates a single-pole, double-throw switch.
A typical circuit consists of a number of rungs, with each rung controlling an output. This output is controlled by a combination of input or output conditions, such as input switches and control relays. The conditions that represent the inputs are connected in series, parallel, or series-parallel to obtain the logic required to drive the output.