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Scale Controller - Change in Weight?

03/07/2012 9:11 AM

Has anyone used a scale controller which has a direct dw/dt display? I want to give my client change in weight display without a PLC.

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#1

Re: Scale Controller - Change in Weight?

03/07/2012 10:10 AM

The closest thing I can think of is the flowable-solids mass flowmeter by Eastern Instruments.

http://easterninstruments.com/products/centriflow.html

Not an endorsement, but I used to work there.

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#2

Re: Scale Controller - Change in Weight?

03/07/2012 10:28 AM

The longer you wait the smaller dw/dt gets. So unless your trying to display a filling or emptying flow rate this won't be very useful information. You certainly could produce an analog circuit of a single pole high pass filter to drive an analog meter to get this displayed. Calibration may become tricky but certainly not impossible.

Oh, my choice of all analog circuitry is not accidental. A PLC only works with discrete time and not continuous time. A PLC can only generate a display of Δw/Δt. I know that I'm nit picking here and that Δw/Δt → dw/dt. Forgive me.

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#3

Re: Scale Controller - Change in Weight?

03/07/2012 10:49 AM

Maybe some more explanation. - Scale platform - Tank being filled slowly on scale - I want to a scale display which will show me rate, instead of having to write down numbers every 15 seconds, and use calculator to determine the rate. This unit can do it but is overkill in complexity for my single platform application. http://www.schenckprocess.de/pdf/unternehmen/komponentenkatalog/en/disomat_t.pdf

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#4

Re: Scale Controller - Change in Weight?

03/07/2012 10:12 PM

I gave you what i thought was a pretty good solution. I would be interested to know why it works/doesn't work for you. After all, I am an engineer.

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#5
In reply to #4

Re: Scale Controller - Change in Weight?

03/08/2012 10:53 AM

Yes, this would work well for measuring powder flow. My application calls for a small tank on scale. Outlet tube with needle valve. - I want to adjust pressure on top of tank, and measure the flow. And adjust needle valve accordingly. I can use a flow meter, but since I need a scale to fill and make a mix in the tank, I wanted to use the instrument I have already.

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