Measurement problem

7 posts in this topic

Hi guys!

I need to measure a sheet thickness. The sheet is going through between rolls. As the sheets thickness changing the rolls getting rise or descend. I have an ultrasonic sensor. My problem is when the thickness is changing like From 1 mm to 2 mm the ultrasonic sensor signal is not changeing in a straight proportion. The sensor working well around at 2.5 mm. I tought about how to calibrate it correctly. If I put first 0.2 mm sheet then i not it down the value of the sensor then put 0.4 mm sheet And so on....and making little sections like how much is the sensor value and decide by my calculation. Do you know anyone a better solution for this ? Also you guys do you think it will work ? I should write the program in rs logix 5000.  Thanks in advance any idea or tips.


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Depending on how close in tolerance you need to be, your plan should work.  You may also want to feed your data in an analytical program you may find an AX + B type formula which works and saves you a bunch of PLC programming.  The LS-7000 that TWS suggests is also an alternate approach worth considering.  Keyence has been good about sending Application Engineers to my facility to get the right sensor when I needed it.  You could also place an LVDT measuring the Center to Center distance change on the rolls as this would give you thickness.  I suspect some of the non-linearity comes from the ultrasonic target being a moving sheet and not a flat stationary target.  You may also have some density changes in your sheet as you change it's thickness that will affect the ultrasonic.

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I can also say that Keyence is good at sending a representative to the facility to look the application over and figure out the best solution to a problem.

What TWS linked is a better solution then what I posted.




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well....i think you need to put some specs together. without posting the numbers, there is no answer.


"measuring sheet", "reading does not change from x1 to x2" etc tell us nothing. 
what is the sensing range" for example 3mm.
what is the minimum sensing distance? for example 1mm (that means range is 1-4mm)
what is the type of signal that your input expects? popular industrial options are 0-10V, 4-20mA, qudrature pulse train etc... or you have something entirely different?
what is the resolution of input that reads the sensor value? 
what is desired accuracy?
what is the environment? dirty and hot like in foundry? any contaminants to worry about? how about noise, radiation etc.?
what is the speed of measurement etc. 

i would guess that you are looking for something with range of no more than 5mm. probably 0-10V rr 4-20mA would do. 10bit resolution or so would probably do. continuous process with sampling rate of no more than 500 samples per second.

in that case, analog inductive sensor may just be a perfect solution. 



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