A few days ago I was heating something in the microwave. I paused it for a moment to check the temperature and then restarted it again. At that time, I remember thinking: "Hmmm, that's strange, I'm sure the turntable has changed direction..."
I think I've noticed this before, but it's one of those things you tend to ponder for a moment and then forget until the next time it happens. I tried pausing the little scamp again and then restarting it, but this time it carried on in the same direction... maybe I was mistaken...
Why am I waffling on about this? Well, as I've mentioned before, I'm a member of the "How Things Work" group on Yahoo. The folks there are really clever, so I tend to keep my head down and just watch the email conversations bounce back and forth. Well, just a few says ago someone posed the following question:
Why does the direction of rotation of the platform in a microwave oven reverse almost each time the oven is started?
What? Someone else has seen the same thing... my observation was not the wanderings of a deranged mind... so I awaited the response in eager anticipation... and almost immediately someone replied:
Probably because the motor driving the turntable is a simple synchronous
motor, which will start and run indifferently in either direction, and will suffer no harm if the rotation of said turntable is blocked.
Old-fashioned synchronous-motor clocks (and I don't know if they exist in the States) have a wee spring which, if the rotor starts up in the "wrong" direction, bounces it back so that the clock runs forwards...
So, another question answered... I don't know why, but I'm much happier for knowing the solution to this little conundrum...
Questions? Comments? Feel free to email me – Clive "Max" Maxfield – at firstname.lastname@example.org). And, of course, if you haven't already done so, don't forget to Sign Up for our weekly Programmable Logic DesignLine Newsletter.