Author Topic: Scale input to Eng. Units  (Read 10126 times)

Mike_PAC

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Scale input to Eng. Units
« on: December 28, 2005, 07:24:01 PM »
 I have a project where I need to measure the height of a box and deal it off to one of many directions according to it's measurement. I am using an ultrasonic transducer to do this. I am inputting this to an 888+ PLC and it works great. My problem is that it is not linear over the entire range. I have a range of 0" to 24" with the 0" representing no box present to the 24" equaling the tallest box. If I have it correct at the max. height then It will be off by 1/2" at the min. height.

 The ultrasonic output is 0-10vdc of which I use a resister network as outlined in the manual to derive a 0 - 5 vdc input. This works correctly.
 
 The formula I am using is B = ((ADC(1) * Z)/4092)
 Z = 2400 which is 24" x 10 to get rid of the real number.
I need to measure down from 0.0" to 24.0"
What am I doing wrong?

Everything works correctly, just that it is not linear. It has to be in my scaling formula.

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Re:Scale input to Eng. Units
« Reply #1 on: December 29, 2005, 12:10:15 AM »
What is the value of ADC(1) you observed on the online monitoring when at minimum? Is it near zero? If it is then your formula should return B = 0 which is correct so I am not really sure what you mean by off by 1/2".

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