My apologies to everyone that responded to my original thread. I had notifications turned off and forgot about this thread! Life took over and this project got benched for a year.

This was my original question

"I am building a dust collection cyclone for my wood shop and assembled a sawdust bin level shutoff circuit but I have a concern. A normally open 110 vac photoelectric switch energizes a dpdt relay and shuts off power to a 40amp motor relay when the sensor see's an object within four inches. My concern is the sawdust in the bin will be swirling around and might trigger the sensor before the bin is full. I dropped a handful of sawdust in front of the photoelectric switch and it rapidly switched the 40amp relay on and off. I do not want this happening to a 5hp compressor duty motor. My thoughts are to integrate a time delay relay that only shuts off the 40amp relay after it has a steady object sensed for at least :30 seconds and ignore intermittent object sensing."


The cyclone is nearly complete and I will soon be after a bin full sensing solution. When I get the cyclone up and running I will test the photoelectric switch with a light bulb to see how it reacts to air currents in the bin.

Thank you for the 555 suggestion. I looks plausible but I need to dust the cobwebs off the electronics knowledge first.

The weight sensing suggestion may not work. I have heard reports that when the cyclone is turned on it lifts the collection bin off the floor through the small section of flexible duct between the cone and the bin.

The capacitance and paddle solutions look like better solutions and are proven in industry. They are expensive through! The bin is plastic so I wonder if that would affect the capacitance type system.

Here's a couple of pictures to give you an idea of what we're talking about. 5hp motor, 16" material handling impeller, 8" inlet and 6" ducting to all the tools. I'm modifying all the dust collection hoods and ports to accept 6" ducting. This has been a monumental project.

 

Wire up a relay as a latching relay driven by the photo detector output so that when the first pulse from the detector happens, the coil of the latching relay is energized and latches it.

Put a NC button in series with the latch coil so that when you press it, it opens the circuit and unlatches the relay. That's your reset button.

Run the coil of the motor contactor through the Normally Closed contacts of this relay such that when it energizes, it cuts power to the blower.

Done!

 

Thanks JohnInTx. What about transient signals from dust swirling around in the bin? Will that activate the latch relay?

I was thinking of a circuit that would ignore transient signals from the photo sensor and only trip a relay when it stayed on for more than :30 seconds.

 

Maybe. I was hoping you could reduce the sensitivity of the PDR to compensate. Other than that, a delay-on-make relay would do the trick.

Attached is a scribble that shows what I had in mind. The 'latch' relay could be a delay-on-make one I think... But you get the idea?

EDIT: you could implement the delay on make function with a 555 or other circuit for sure but that means cobbing together a circuit that you could just go out and buy. Depends on whether you want to play w/electronics or just get back to sawing wood.

TDR info right here on AAC

Something like this between the PhotoDetector relay and the latching relay would likely do the delay function just fine.
Maybe this would be better since its for driving contactor type loads..

 

Thanks John. I will do some research.

 

Currently working on a dust collection system powered by a 150Hp blower, baghouse, roots blower for transfer to a holding bin, then screw fed discharge into truck bins. They use ultrasonic rods for level sensing, along with an add on capacitive sensor. Sure they are quite pricey.

Back to the paddle thing. If you drive a paddle with a small DC gearmotor, all you need to do is compare current over a shunt to some voltage reference. When your dust levels impede the rotation, increased currents (voltage over a shunt) will switch your comparator. A simple smoothing filter (resistor/cap) can be included if required.

 

Thanks GetDeviceInfo. A 150hp dust collector! Holy cow. I assume that system is designed to have all blast gates open at the same time? What size ducting is being used? What kind of cfm and velocity are they aiming for? What kind of material is being transferred?

The paddle system is my plan B if the photo sensor doesn't work. I started researching it this morning.

Someone in the original thread mentioned dust covering the photo eye and triggering a false indication. We will see when I get this thing up and running.

 

Thanks GetDeviceInfo. A 150hp dust collector! Holy cow. I assume that system is designed to have all blast gates open at the same time? What size ducting is being used? What kind of cfm and velocity are they aiming for? What kind of material is being transferred?

The paddle system is my plan B if the photo sensor doesn't work. I started researching it this morning.

Someone in the original thread mentioned dust covering the photo eye and triggering a false indication. We will see when I get this thing up and running.

Dust collection for automated wood Ibeam manufacturer. This is actually the smaller system with the larger at a 200hp blower. Both systems implement a water quenching system where sensors look for sparks, then spray water into the conveying stream for a timed period. Blast/abort gates open together. I personally don't get into the math of conveyance, but because the facility does have a couple of larger natural gas drying furnaces, I keep an eye on pressure balances and associated interlocks.