Author Topic: Relay noise with DS12A door sensor  (Read 3617 times)

woodyl

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Relay noise with DS12A door sensor
« on: August 26, 2013, 09:00:33 AM »
I'm hoping that someone can help me with this problem.  I have installed a photoelectric beam sensor and I've connected the "normally open" contacts to a DS12A RF door sensor.  So, when the beam is in "light off" state, the circuit is closed and the DS12A sends "normal".  When the beam is in "light on" state, the circuit opens and the DS12A sends "alert".

This setup works ok in the "light off" state in which the circuit is closed.  When the device goes to "light on" and the relay circuit is open, the DS12A goes wild and starts sending a continuous stream of "alert" and "normal" indications.  These are sent until the photo beam sensor is unplugged or else goes back into "light off" condition.  I've tried this with 2 different DS12A devices, and both reacted the same.

When the photo beam relay is in the open state, I can measure  3V AC across the leads, and I'm assuming that this is some form of noise that the DS12A is reacting to.  I believe that the sensing current used by the DS12A is at around 3V, so it makes sense that it would react to this current.

I would guess that there's a way to filter this relay circuit using resistors and/or diodes, but I don't know how to do it.  I would appreciate some advice on how to get this to work.

Brian H

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Re: Relay noise with DS12A door sensor
« Reply #1 on: August 26, 2013, 09:43:50 AM »
Are you sure it is a dry contact relay output?
How long is the wiring between the DS12A and the Photo Sensor?

woodyl

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Re: Relay noise with DS12A door sensor
« Reply #2 on: August 26, 2013, 10:32:27 AM »
Everything I see suggests that it's a dry contact relay, plus, the problem is occurring when the relay is open.  This is a description of the photo sensor: http://www.seco-larm.com/E960Sb.htm

The run from the photo sensor to the DS12A is probably about 20 feet.  I'm going to wire up a DS12A close to the photo sensor and see if that changes anything.

Brian H

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Re: Relay noise with DS12A door sensor
« Reply #3 on: August 26, 2013, 12:04:17 PM »
Yes the literature shows a dry contact relay in it.
The schematic for the DS12 shows the input going directly into a pin on a EMP78P153S IC through a 1K resistor.
My guess the IC  may have an internal weak pull up internally  as I have not found an English data sheet.
« Last Edit: August 26, 2013, 01:30:54 PM by Brian H »

woodyl

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Re: Relay noise with DS12A door sensor
« Reply #4 on: August 26, 2013, 02:59:48 PM »
Any suggestions on how to filter out the noise on this setup?

Brian H

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Re: Relay noise with DS12A door sensor
« Reply #5 on: August 27, 2013, 05:59:24 AM »
I noticed the photo beam has a wide power specification.  Are you running it on 120 VAC?

You may want to try a .1uf cap across the external sensor input or maybe using a twisted pair of wires between the photo beam and the DS12A.

woodyl

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Re: Relay noise with DS12A door sensor
« Reply #6 on: August 27, 2013, 12:13:46 PM »
I noticed the photo beam has a wide power specification.  Are you running it on 120 VAC?

You may want to try a .1uf cap across the external sensor input or maybe using a twisted pair of wires between the photo beam and the DS12A.

I tried powering the photo beam with both AC and DC and had noise problems with both.  The good news is that I added the capacitor, as you suggested, and it seems to have taken care of the problem!  This was a simple solution and seems to work well whether I'm using AC or DC power.  As far as the wiring, I probably should have used twisted pair phone wire, but now it seems to working well with the capacitor.  Thanks for your help!

 

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