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Analog input scaling for large values

Created by: Abed.Al at: 6/24/2014 12:29 PM (13 Replies)

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7/3/2014 11:46 AM	Rate (0)
Abed.Al Advanced Member Joined: 12/6/2011 Last visit: 7/3/2025 Posts: 33 Rating: (0)	Why would I NORM the value from 0.0-1.0 instead of 0.0-27648 ?

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7/3/2014 12:27 PM	Rate (1)
William_B Posts: 5225 Rating: (1204)	Eng. L Why would I NORM the value from 0.0-1.0 instead of 0.0-27648 ? Hi. That is what the NORM function does. It normalize an input to a value between 0.0 and 1.0. You can not change this.. it is fixed. Then SCALE assume you have a value between 0.0 and 1.0 to scale between two user defined values. Again you have no choice of what the scaling is of the input parameter. NORM and SCALE work together to rescale a value to other limits. I'm sure it makes sense to someone.. even if it does not make sense for you and I. You could develop your own scaling algorithm.. I had something in the S7-200 (using a Siemens application note).. call it RESCALE if you wish. I fyou want to know more about this.. I invite you to search the S7-200 forum group. Frankly using NORM and then SCALE is easy enough. Just remember to use both code blocks. Using these standard blocks also has the advantage of giving you the choice of selecting the data type for the input and output variables to these code blocks. Hope this helps. w
William_B Posts: 5225 Rating: (1204)
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7/3/2014 12:40 PM	Rate (0)
Abed.Al Advanced Member Joined: 12/6/2011 Last visit: 7/3/2025 Posts: 33 Rating: (0)	Thanks! But the manual says to NORM from 0-27648 NOT from 0-1.0 .. That thing I still don't understand. And in the S7-200, I used to get a value of 32xxx on the ananlog input word when I fed the input of a constant +10 VDC!!

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7/3/2014 2:11 PM	Rate (1)
0_Einstein Grandmaster-Expert Joined: 7/7/2010 Last visit: 12/31/2025 Posts: 16342 Rating: (2521)	Eng. L Thanks! But the manual says to NORM from 0-27648 NOT from 0-1.0 .. That thing I still don't understand. And in the S7-200, I used to get a value of 32xxx on the ananlog input word when I fed the input of a constant +10 VDC!! The NORM function takes any input and scales TO 0.0 to 1.0. If the input is a standard analog input signal, range of the NORM INPUT is 0..27648. As to the out of range error value, unless your scale puts out 10.0 V and you actually use it to full range (nobody does that), there is nothing to worry about. If you inject 10.0V with a calibrated voltage source into the analog input, you may find if you reduce the voltage a few mV, the reading should drop quickly to 27648 counts. The analog input hardware is not perfect and may calculate 10.0V ever so slightly differently than your calibrated voltage source. If you are not using a calibrated voltage source, perhaps it is slightly greater than 10.0V which puts the analog input input an overrange condition. You can see an overrange condition by one of the high bits (those that cause the value to exceed 27648).
	science guy
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