How to Test Relays With a Multimeter

How to Test Relays With a Multimeter

A relay is one of the most versatile, durable and dependable components you'll find in any electronic device. A relay allows current to be switched from one circuit to another by using electromagnets in a simple way. It can be found everywhere from simple household appliances to complex computers and communication networks. In a relay, electrical inputs act as triggers that activate electromagnets to establish or disrupt circuits. This process translates feeble electrical signals into the higher amperage levels needed to power devices with high-current demands.

Relays are used in a wide range of applications, but there are some common problems that you can check for yourself with your multimeter and a few easy steps. First, locate the relay's connection point, which is typically marked with pins or terminals. Next, probe the point with your multimeter set to read voltage. If you don't detect a voltage, the problem lies elsewhere in the circuit. If you do detect voltage, then use the continuity function to test for a good ground connection on the opposite side of the relay plug.

If you are able to locate the relay's connections, you can then look at how many poles it has and its normally open (NO) and normally closed (NC) contacts. You can also find this information on the relay casing or in its datasheet. The pole count refers to how many sets of switches are connected to the same actuator, and the number of poles is often represented as a double-throw or SPDT relay, meaning it has two switch elements actuated by the same coil. The electrical specifications for the coil and the internal switching contacts will also be labeled, such as a coil voltage rating and a contact current rating.

The contact sequence of a relay is often described as "make before break." This means that the first contact in a set is opened when the coil is de-energized, and then closed when the coil is energized again. This ensures that the signal is not dropped as it is transmitted over long telegraph lines. This same logic is used to control many modern computer processors, allowing them to be powered at a rate that does not exceed their output capacity. Specialized relays, such as time-delay ones, can add a whole new level of complexity by enabling them to be triggered at specific intervals and then powering devices in repeating cycles. This is what enables things like flashers and amusement park rides to work as designed. These are just some examples of how the clever little magnetic switches are used. The list is virtually endless. You'll even find them in cars, washing machines, and air conditioning systems. The power that drives them all is the same: electricity. But the brilliance of a relay is in its ability to convert this current into complex and precise commands, bridging gaps that would otherwise require a network of expensive and complicated components to accomplish. A solitary relay can orchestrate the activation of multiple different circuits, granting it the capability to perform Boolean logic functions that rival those of many more costly and intricate devices.

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