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Old 11th November 2009, 01:34 PM   #1
Default Simple delay for Sensor

Hi
I have a proximity sensor thats output is connected to a PLC in a piece of equipment. Its function is to shut the machine down when metal is detected. What happens is when metal is detected by the sensor 24Vdc is supplied to a pin on the PCL, the PLC then instantly shuts the machine down.

What I need to do is intercept the 24Vdc ,wait a few seconds and then send it to the PCL. If the 24Vdc is lost during the wait time then start the wait time over.

Anyone have a circuit for this?

Thanks
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Old 11th November 2009, 03:05 PM   #2
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What power supply voltage is available?

Are you adverse to using a small relay?
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Old 11th November 2009, 03:51 PM   #3
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24Vdc or 120Vac are the only voltages available except for the 480 3 phase. I would prefer to use an electronic device as apposed to a relay. Since the sensor will be cycling continuously. In other words metal objects pass the sensor all the time. I just want the signal sent to the PLC if the sensor detects metal for several seconds.

HTH
Thanks
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Old 11th November 2009, 05:21 PM   #4
Default

Custom designed just for you
Attached Thumbnails
Simple delay for Sensor-draft27.gif  
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Old 12th November 2009, 12:30 AM   #5
Default

Mike, This looks great but I have questions,
Could you provide more details as to the wattage of the resistors and the types of caps in the circuit.

If I am reading the graph correctly at the bottom the delay looks to be about 2 seconds which is exactly what I need. Would it be difficult to add a pot to vary the delay a few seconds +-. (not necessary just an option)

What does the RC at C1 represent. Is it just a reference point for the current input voltage. I am just now at 50 and trying to learn something new. So some of these questions may sound dumb.

Thanks
TimK
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Old 12th November 2009, 01:23 AM   #6
Default Plc

TimK

You should be able to make some very slight program changes in the PLC by adding a timer and let the PLC do the delay for you???

What brand of PLC is being used?
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Old 12th November 2009, 05:46 AM   #7
Default

Quote:
Originally Posted by TimK View Post
Mike, This looks great but I have questions,
Could you provide more details as to the wattage of the resistors and the types of caps in the circuit.

If I am reading the graph correctly at the bottom the delay looks to be about 2 seconds which is exactly what I need. Would it be difficult to add a pot to vary the delay a few seconds +-. (not necessary just an option)

What does the RC at C1 represent. Is it just a reference point for the current input voltage. I am just now at 50 and trying to learn something new. So some of these questions may sound dumb.

Thanks
TimK
Revised schematic attached. The "RC" is just a node label so that I could plot that node. I added a 1megΩ Pot to vary the delay. The caps over 1uF are 15V electrolytics. The 100nF is just a bypass, non polarized. All resistors are 1/4W metal film. The Zener is 1/2W 12V. The 555 is available from lots of sources.

Except for the Zener and the Pot, you might even be able to get the parts at RatShack
Attached Thumbnails
Simple delay for Sensor-draft27.gif  
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Last edited by MikeMl; 12th November 2009 at 05:48 AM.
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Old 12th November 2009, 01:25 PM   #8
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Thanks Mike
This is great.

And Hey! Be Nice, I used to manage a "RatShack" LOL But that was back before they became a retail outlet for other brands.

I am going to try my hand at designing a PCB. When I get it done I will post it here. Maybe you could look at it to make sure I dont shut down the power to the central US or something.

Thanks Again
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