Simple delay for Sensor - Electronic Circuits Projects Diagrams Free

TimK · 11th November 2009, 01:34 PM

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

MikeMl · 11th November 2009, 03:05 PM

What power supply voltage is available?

Are you adverse to using a small relay?

TimK · 11th November 2009, 03:51 PM

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

MikeMl · 11th November 2009, 05:21 PM

Custom designed just for you

TimK · 12th November 2009, 12:30 AM

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

odps · 12th November 2009, 01:23 AM

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?

MikeMl · 12th November 2009, 05:46 AM

Quote:

Originally Posted by TimK

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

TimK · 12th November 2009, 01:25 PM

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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11th November 2009, 01:34 PM	#1
TimK	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 __________________ clueless

11th November 2009, 03:05 PM	#2
MikeMl	What power supply voltage is available? Are you adverse to using a small relay? __________________ Mike ML.

11th November 2009, 03:51 PM	#3
TimK	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 __________________ clueless

11th November 2009, 05:21 PM	#4
MikeMl	Custom designed just for you Attached Thumbnails __________________ Mike ML.

12th November 2009, 12:30 AM	#5
TimK	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 __________________ clueless

12th November 2009, 01:23 AM	#6
odps	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?

12th November 2009, 01:25 PM	#8
TimK	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 __________________ clueless