Mechanical Relay Primer

Introduction

Mechanical relays are designed to turn on or turn off the power supplied to other devices using a simple signal from a digital output. They are similar to Solid State Relays except they are less expensive, but are also less sophisticated and have a shorter lifespan. You can use them to control LEDs, heaters, appliances, and generally powered device as long as the power you're switching falls within the limits of the relay you're using.

How it works

Mechanical relays use a simple electromagnet to open or close the circuit. When current runs through the input and energizes the coil, it creates a small magnetic field which either pulls the arm of the switch away from the other contact of the switch, or pushes it down to close the switch depending on the how the switch is made.

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Basic Use

Controlling a mechanical relay is as easy as turning on an LED. Any Phidgets device with a Digital Output should be able to control a mechanical relay.

Contact Bounce

As with any mechanical switch, relays are susceptible to contact bounce. This means that when the switch closes, the arm can bounce on the contact, causing the load's power to flicker slightly. This usually only matters when the application is detecting when the power signal turns on. For example, a circuit designed to increment a counter every time power is applied to its input could incorrectly interpret a bouncing switch as multiple events. Check the switch primer for information on how to deal with switch bounce. It's worth noting that Solid State Relays don't suffer from contact bounce, because the operate without using moving mechanical parts.

How to choose

• What are the parameters for deciding which product to buy?
• If a customer called and wanted to know which product to buy you would initially ask "What do you want this for?" Build this section as if you were continuing to ask the further questions you would need to help the customer decide what to buy. Help them figure what product to buy/why buy the product without them actually having to call us.

Types or Classes

• Analyse commonalities of the product family and categorize the individual products into the classes
• There should be very few products with exceptions.
• Explain the distinguishing parameter for each class of product
• Explain the differences between each class and all the other classes.
• Make sure the class distinctions are different enough- and only split classes for characteristics that are important enough
• This section should assist the customer in making their selection criteria easier to determine.

Conclusion

• Much the same as the Introduction, but using reference to supplied information to justify the statements.

How to buy

• Table of products, divided into classes discussed above, and individually linked
• This section could be auto-generated eventually