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From: "Roger Lascelles"
Subject: Re: measure acceleration
Date: Mon, 23 Dec 2002 17:41:11 +1100
X-Newsreader: Microsoft Outlook Express 5.50.4133.2400
I worked for a garage door opener company.
We sensed motor current for the 24V DC motor, using a 0.1 ohm series
resitor. Two pots were provided to set the up and down trip current.
I think the AC motor used a speed sense trip, which sensed motor slowdown /
stall. A magnet and hall effect sensor fed pulses which triggered a
monostable - if time between pulses was too long to retrigger the monostable
then the monostable timed out and turned off the motor.
Both AC & DC systems had a short delay at start up which disabled the turn
off, to give the motor time to get spinning.
"James Meyer" wrote in message
> On 22 Dec 2002 13:49:50 GMT, email@example.com (PDRUNEN) wroth:
> >Hi Group,
> >Looking for a means to detect a hard stall of a garage door coming down
> >8 to 12 inches per second. I don't need to have a exact value for
> >but a step value for a hard impact on a ladder or such.
> >I see some interesting chips from Analog Devices, however, a mechnical
> >is Ok to.
> I would use a "tape switch" along the bottom edge of the door.
> A tape switch is essentially a rubber tube with a pair of conductive
> strips placed inside the tube along its length. The strips are placed
> top and bottom of the tube. When the tube encounters an obstacle, it is
> so that the two conductors touch each other. Use the switch closure and a
> to cut off the motor power. The switch will work no matter what speed the
> is moving.
> The neat part is that if the switch is installed properly, it serves as
> a gasket at the bottom of the door to keep water and cold air out at the
> time. Plus, you simply buy the switch, possibly cut it to length, and
> it. Should be an easy afternoon's project.
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