As discussed in my last post, Electronic Testing 101: Questions to ask when Reviewing Test Specs or Outlining Reqs, no one relay will operate from say millivolts to 1,000 volts at a frequency range to DC to 18 GHz. As more and more devices combine digital, analog, and RF/Microwave, you as a test engineer will likely be required to select many different relay choices for your test system. So, let's look at the various relay types in the market, where they excel and where they should not be used.
Solid state relay using Two N Channel MOSFETs with an Isolated Gate Drive
In my last post (Testing 101: Questions to ask when reviewing test specs or outlining requirements), I talked about understanding what the test specifications are. Now that we are talking about relay types, the key specs to focus on are:
Voltage, current, and bandwidth are probably the most obvious. Where you can get in trouble is the last two. Ohm’s Law tells me that if I select a relay rated at 150 Volts at 1 Amp, I expect to switch up to 150 watts, right? That could be wrong. If the relay is rated at 150 Volts at 1 Amp AND 60 watts of power, that means that you can switch 150 volts OR 1 Amp. Any spec in between is derated. Finally, relays like reeds and EMRs are rated for the number of cycles at a given load. So, a reed relay rated for 10 to the ninth cycles at a low power application (100ma or less) might be rated at 10 to the sixth cycles at full power rating– several orders of magnitude less— this needs to be factored into your maintenance schedule.
As always, comments and/or questions are welcome. If this blog series is valuable to you, be sure to share the link with your colleagues.
For more information about relays, check out our other resources such as the "What is a Reed Relay?" video and our Switchmate eBook. Watch the on-demand webinar: Maximizing Reliability in Signal Switching to learn the importance of switching in test systems.