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Author Topic: Load Cell Amplifier with Analogue Output  (Read 5671 times)
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QuAdR
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« on: March 17, 2011, 11:17:04 23:17 »

i need loadcell amplifier pcb.i wanna convert mv to 0-10v.

like this link;

http://www.loadcells.com/PDF/Load-Cell-Amplifier-LAC74.1.pdf
« Last Edit: March 19, 2011, 12:03:04 00:03 by pickit2 » Logged
LabVIEWguru
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« Reply #1 on: March 18, 2011, 01:54:02 01:54 »

Linear Tech at linear.com has application notes on the subject.
Analog devices also has application notes on the subject.
Maxim has amplifiers specifically adapted for load cells, last I looked.

You are going to need an instrumentation amp, a +/- supply, and another opamp to offset the output of the
instrumentation amp. Have a look at the app notes, and  if you have specific questions I'll try to help you.

Depending on where you are at, I might try to find a junk store that has a digital bathroom scale you can buy cheap.
Then you can tear it apart and figure out how it works.
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QuAdR
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« Reply #2 on: March 18, 2011, 02:33:27 14:33 »

i found this document but i haven't any idea. Sad if you know any project please tell me
[co-de]
http://circuits.linear.com/images/circuits/23_circuit_1.jpg
[/co
de]

thanks.

Edit: Don't code links
« Last Edit: March 19, 2011, 12:01:45 00:01 by pickit2 » Logged
MGLSOFT
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« Reply #3 on: March 18, 2011, 04:14:36 16:14 »

See the web page of Scaime...
http://www.scaime.com/en/352/produit/digital-weighing-transmitter-board.html
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« Reply #4 on: March 18, 2011, 06:19:28 18:19 »

QuAdR - Maybe we need to start over - what are you trying to do? Is this for a hobby or a product? What are you starting with? Do you want to build or buy an amplifier? (do you want a kit?) Do you have a 350 ohm bridge strain gauge? What will your application be? Will you run from batteries? What resolution do you need? What country are you in? Do you have an electronic background? Do you have access to parts? Do you want to eventually use an A/D?  I have designed and built a number of commercial strain gauge instruments but I need to know where to start.


The circuit is OK as far as it goes, but the strain gauge will have to be positioned so it reads only "forward" or flexing in one direction only. This is probably OK if you are building a weigh scale. If you want to build a flowmeter or an instrument that detects how much a bridge (the kind that cars drive over) you need a circuit that supplies +/- because you want to measure how much the gauge flexes either way.
« Last Edit: March 18, 2011, 06:31:20 18:31 by LabVIEWguru » Logged
cerebronico
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« Reply #5 on: March 18, 2011, 10:54:35 22:54 »

@LabViewGuru

It's easy to note you have a lot of experience in weighing systems, so I have to ask you a question, would you please give me some idea on how can i measure the rate of gain/loss of weight, for example: i have a hopper with a rotative valve attached to an AC driver so y can control its speed, and i want to maintain a continuous rate of X kg/s, what should I need besides the load cells and an encoder as i see in some commercial systems? how they relate speed to weigh?

Any help would be truly appreciated,

best regards,

j
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QuAdR
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« Reply #6 on: March 18, 2011, 11:05:56 23:05 »

@LabVIEWguru
sorry i can explain.
Quote
Do you want to build or buy an amplifier?
i want to build amplifier.

i have a loadcell.i wanna connect loadcell direct to plc.but plc card is just running 0-10v.i must convert to 0-10v.plc analog input 16 bit.



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« Reply #7 on: March 18, 2011, 11:28:36 23:28 »

cerebronico - they make "batching controllers" or "mass controllers" that do just as you have explained. They have load cell amplifiers on-board, so you just connect the load cells to the back of the unit. Most are PID settings, so you have to experiment a bit. Omega sells units to do this, there is another company - I'll hunt the name up and post it later - that makes a real attractive unit with all types of settings.

Posted on: March 18, 2011, 11:25:31 23:25 - Automerged

Quadar - if you want to weigh bags of dope, I don't care. If I'm going to inadvertently help someone build a personnel sensor for trip-mines, that would bother me a lot.

That said, every PLC manufacturer I've ever seen sells analog input cards for strain gauge applications. Good luck.
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QuAdR
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« Reply #8 on: March 28, 2011, 02:45:14 02:45 »

i found this page and this picture.how can i stable output voltage.0-10v

http://www.nakka-rocketry.net/strainlc.html
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EDSONCT
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« Reply #9 on: March 28, 2011, 12:30:16 12:30 »

You can use a rail-to-rail do amplifier signal, but use reference supply in load cell.
Edson
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