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Pickering Electronics Blog

Relay Operating Temperature Effects

Posted by Graham Dale on Jun 11, 2015 12:30:00 PM

 

Reed Relays are sometimes considered a mundane component by design engineers and often little thought is given to their operating parameters. One of these parameters is operating temperature and failure to consider its effects can lead to the possibility of the relay not operating at high temperatures.

The relay’s reed switch is operated by a magnetic field generated by a coil which is wound around it using copper wire. Copper has a positive coefficient of resistance of approximately 0.4% per °C and its resistance will increase with temperature at this rate. As the resistance increases, the current and therefore the level of magnetic field will fall.

 

Distribution of Operate Voltages

The industry standard ‘Must Operate Voltage’ sometimes called the ‘Pull-In Voltage’ is 75% of nominal and usually quoted at 25°C. For a 5V relay this would be equal to 3.75V, although in practice it will be lower than this figure. The first graph below shows the actual distribution of Operate Voltages for a batch of 1000 Pickering relays. In the second graph you can see how this operate voltage figure will change with temperature.

 

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Topics: Reed Relays, Operating Temperature Effects

The unique features of Pickering Reed Relays

Posted by Graham Dale on Apr 28, 2015 12:00:00 PM

 

Reed Relays remain an attractive solution for switching applications. Having a metallic path, they do not suffer from a relatively high contact resistance and high off-state leakage current usually associated with solid state relays. Having hermetically sealed contacts, reed relays offer a better low level performance than conventional electro-mechanical relays as they do not suffer from oxidization or films building up on the contacts. They also have the advantage of faster operate and release times, critical in today’s instrumentation and test systems.

Unfortunately though, relays are often considered a mundane component and little thought is given to them by the design engineer which can lead to problems.

In general, the most common construction for a reed relay offers no magnetic screening, involves the use of a hard moulded package and an operating coil wound on a plastic bobbin surrounding the reed switch capsule. Pickering offer a technically superior solution.

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Topics: Reed Relays, High Density Applications

An introduction to Reed Relay basics (Part 2): The Configurations

Posted by Graham Dale on Mar 24, 2015 12:30:00 PM

 

Normally Closed Reeds

 

Normally open reed relays are by far the most common configuration of reed relay. However, normally closed relays can also be supplied where the blade is biased so it is normally closed and the application of a magnetic field opens the relay contacts.

The contact bias is created by adding an internal permanent magnet to hold the reed switch in a normally closed state. When the relay coil is energised it cancels out the magnetic field bias and the contacts open. If the coil voltage is increased substantially beyond its nominal voltage (typically greater than 1.5 times nominal) there is a risk that the contact will reclose.

Not surprisingly normally closed relays are more difficult to manufacture and have higher magnetic interaction due to the bias magnet.

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Topics: Reed Switch, Two Pole Relays, Changeover Reed, Normally Closed Relay

An introduction to Reed Relay basics (Part 1):

Posted by Graham Dale on Feb 25, 2015 10:18:44 AM

What is a Reed Relay?

Reed relays contain a reed switch, a coil for creating a magnetic field, an optional diode for handling back EMF from the coil, a package and a method of connecting to the reed switch and the coil to outside of the package. The reed switch is a simple device and relatively low cost to manufacture.

 

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Topics: Reed Relays, Reed Switch