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Clay B.

Sensing Plastic

9 posts in this topic

Ok here is my delima. We unload plastic from rail cars using a Vacuum Blower System. As you can guess clogs are an issue. The pipes are 4" for one system 6" for the other. Does anybody know of a way to monitor the volume of plastic in the pipe while it is moving. What I want to do is see if the pipe is filling up and stop the system before it cloggs up completely. I am looking for an off the shelf item. I have looked at anlog out capasitive prox's but at the speed the plastic is moving the senssor itself creates clogs. My thought is a capasitive sensor that is made into a pipe coupling so nothing is protruding into the flow of plastic. If anybody has any suggestions or has already been down this road your insight would be very helpful. Thanks Clay

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The load on your vacuum blower motor will be directly proportional to the mass of the air it is moving through it. Think about this - what happens to your vacuum cleaner at home when you put your hand over the hose? You hear the motor speed up right? This is because the load on the motor drops. So monitoring motor load should tell you how much air you are moving. When the pipe gets blocked the blower load should decrease. But you can't just measure motor amps, you need to monitor active power. Check out http://www.loadcontrols.com. They have three phase sensors designed to do that. They come with analog outputs and adjustable alarm relay outputs. Give them a call, they are a helpful bunch.

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it may not be plastic, but we are blowing powders all over the palce here where I work. We use a combination of the following. 1. Pipe Pressure in PSI - Plugs mean Hi Pressure, Blown Lines mean Ultra lo pressure 2. Blower Temp - Plugs heat up some blowers wnile blown lines heat up other styles. 3. Power Draw if the Blower happens to be on a VFD. You might search for Mass Flowmeters and see if they would work also.

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Try these guys. K-Tron Their systems are a bit sophisticated for my taste but superior in function. We use smaller systems to feed extrusion machines.

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We blow stuff around in all of our plants. The easiest way to monitor is like Bob said -- monitor pressure. I've even done systems where we used the line pressure as the input to a PID that was controlling the rate we were feeding product into the blower lines. This was done to 1) prevent chokes, and 2) optimize throughput to conditions and distance transferred.

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I agree that measuring pressure will tell me when my pipe is clogged. What I am is trying to do is prevent the clog in the first place. What happens from time to time is the volume coming from the rail car varries, when this happens 2 things happen next. First is we dump to much material into the cyclone and fill it up or we create a clog in the line coming from the rail car. Also on one unloader system I have one pump that works both as a vacuum and a blower and it is a real pain in the rear. Right now I balance it with my ear and a butterfly valve. Mainly I was looking to kill 2 birds with one stone. I wanted to monitor the flow of material and the volume and adjust my vacuum pump accordingly. Also when my material level in the feed pipe dropped off (rail car is empty) shut the system down. I know I can do most of this thru monitoring the pressure but I was hoping to not have to figure all the pressure levels out. Also the distance I am pulling from varies depending on which rail car I am attached to. So flow rates will not be liner to pressure. I guess if it was easy someone else would get the job. As always any imformation will be apriciated. Thanks Clay

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I still recomend looking at the blower motor power consumption. It takes energy to move anything, be it air or air with entrained material. And that energy is proportional to the mass of what you are moving. Its basic physics. If you move it farther you use more energy only because you spend a longer time moving it, but the energy you use per second - that's horsepower (1 hp is 550*pound*feet/second) - is the same. Since flow is proportional to motor speed, pressure is proportional to motor speed^2, and power is proportional to motor speed^3 then maybe you can monitor the motor power consumption and line pressure - you will probably have to log some data points for a while before you can determine exactly how to detect that you are beginning to clog. Edited by Alaric

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Siemens' Sitrans AS100 is an ultrasonic sensor which outputs a signal proportional to the ultrasonic noise in metallic piping as stuff flows through it. There's an electronics module the CU-02 that outputs a 4-20mA signal or alarm relay outputs. I know where it was used very successfully to monitor the pneumatic transfer of sand. The engineer had to monitor the results to determine what levels represented what flow rates. https://pia.khe.siemens.com/index.aspx?nr=5875 https://pia.khe.siemens.com/index.aspx?nr=5876

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These look interesting. I never thought about using sound to measure flow. Should have though. I check the system alot of the time by placing my hand on the pipe and feeling for the plastic pellets hitting the side of the pipe.

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