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Unread September 14th, 2019, 01:44 PM   #1
Hossamhegab
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Load cells and Analog input scaling in tia portal

Dear all
Iam using three load cells connected in parallel to calibrate the weight of a product but in don't have a weighting module in my system., I just used the analog input on my cpu 1215C (s7-1200) . But I have a problem in scaling the analog input and display ithe weight on the HMI
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Unread September 14th, 2019, 04:40 PM   #2
Ken Moore
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Unread September 14th, 2019, 07:42 PM   #3
JesperMP
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You cannot use a regular 0-10V or 4-20mA input with a loadcell or parallel connected loadcells.
The change in resistance is very small. The weak signal is measured in a socalled "wheatston bridge" configuration (https://en.wikipedia.org/wiki/Wheatstone_bridge).

When applied with an excitation voltage (typically 10V or in that magnitiude), it returns a signal in the mV range (typically 1mV/V, 2mV/V or 4mV/V). The wheatstone bridge helps with compensating for differences in the wiring to/from the loadcell.
You usually have between 4 an 6 leads from each loadcell, so I wonder how you have managed to connect it to a regular analog PLC input.
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Unread September 16th, 2019, 08:31 AM   #4
James Mcquade
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JesperMP is right,
if you are using 3 load cells to weigh something, you must use a summation system controller that is compatible or configurable with the load cells, program the unit, and then take its output and goto the plc.

we have over 50 of such systems here with load cells ranging from, 10k to 250k

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Unread September 16th, 2019, 04:56 PM   #5
Hossamhegab
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I have wired three load cells in parallel and by using load cell ampilifier with 0-10v output , I scaled the analog input from 0 to 150kg . Now it works quite well
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