A relay can control a circuit, device, machine, etc by opening or closing the Electro-mechanical relay contacts. Again check for the continuity between the pole and NO contact. Whenever the base terminal is supplied with an appropriate current, NPN transistor is driven into saturation mode and hence it completes the path from supply to ground. So, AC relays are constructed with special mechanism such that continues magnetism is provided in order to avoid above problem. Alternative to the above discussed transistor and timer based driver circuits, relay driver ICs can drive multiple devices. Protective relays are used to ensure the smooth operation of any power system such that they isolate the particular circuit or generate the alarm whenever parameters like voltage or current exceeds their limits. See also: relay. The number of poles of a relay indicates the how many individual circuits it can control while the number of throws defines the number of different outputs to be connected to input by each pole. Relay is a switch which senses fault in a system and once fault is sensed by the Relay, it issues trip command to the Circuit Breaker, CB to isolate the faulty section of the network from the healthy section. The construction is somewhat different for AC and DC relays, but both work on the principle of electromagnetic induction. These drives are ICs are of different types such as bipolar transistor driven ICs, Darlington pair driven ICs, MOSFET bridge type ICs, etc with various channel configuration like 8 channel, 16 channel, and so on. An electromechanical relay logic circuit can be represented as an electrical network of lines or rungs where each line or rung have continuity for enabling the output device. Finally remove the power supply. Place the multimeter probes such that one probe at pole and other at NO contact and check for the discontinuity between the pole and NO contact. So when the base of NPN has Volt the relay will get the normal Negative Volt and when the base of PNP has no Volt the Positive Volt will reach the relay positive pin, therefore, the relay is one in this condition but, in the base of PNP has Volt the relay has no Positive Volt and it will not activate. The figures below illustrate the relay operation. Best Robot Dog Toys In case of a small amount of voltage ratings, protection of the circuit depends on the cost of the original circuit to be protected and cost of the protection system essential to protect the circuit. Is that feasible? Best Power Supplies In case of NO, NC and COM terminals (not shown in figure), both NO and COM terminals are get contact when the relay get energized while NC contact remains floating. All these relays are working on the principle of electromagnetic attraction. Place the multimeter probes such that one probe at pole and other at NC contact and check for the continuity. This article gives you a brief idea on the electromechanical relay and also different types of relays. Manual operation for switching a relay is performed through push buttons and other conventional switches. The relay is an electromechanical switch used as a protecting device and also as a controlling device for various circuits, equipments, and electrical networks in a power system. When auxiliary relay coil is energized by a transistor driver circuit, the path of the main relay is completed through relay 1 contacts. Thus the relay 2 coil is energized and hence it is operated to turn the heater. Basically, a relay has three contacts which are necessary to connect the two circuits but the way these contacts are configured or switching action of the contacts, relays are classified into different types. 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