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Author Topic: vehicle scale system  (Read 1399 times)
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falcon _bd
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« on: August 24, 2008, 09:23:12 21:23 »

I am going to start a project about vehicle scale system with load cell. so i need some one's help who practically work with this.
please advice me 
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Kwaigo
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« Reply #1 on: September 02, 2008, 09:38:54 21:38 »

Hello. You mean deformable aluminium beam with film resistor? What is your load cell?
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falcon _bd
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« Reply #2 on: September 03, 2008, 01:41:34 01:41 »

i am using the load cell from chinesesensor

http://www.chinesesensor.com/index.php/load-cell/bridge-style/13-bridge-style-load-cell/6-czl-110
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Kwaigo
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« Reply #3 on: September 03, 2008, 11:16:59 11:16 »

This is a resistive bridge sensor. Like in ordinary electronic scale.
Use 24bit delta-sigma ADC (ADS1251 for example). Put AD reference voltage to one bridge diagonal, and other diagonal connect to differential AD input. 24bit resolution enough to exclude preamplifer, because LSB few times less than noise. Some ADC contain PGA at input. You can use it.
Software must obtain two calibration values: zero load and full scale(or part of it).
If scale must be precise in wide temperature range, You need also temperature sensor and temperature compensation value.
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falcon _bd
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« Reply #4 on: September 03, 2008, 01:27:24 13:27 »

But I want to use pic 16f887 . which has  10 bit ADC . is that resolution  is not enough ? can you please explain the full project in block diagram with pic MCU.
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Kwaigo
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« Reply #5 on: September 03, 2008, 09:42:51 21:42 »

1) Internal 10 bit ADC have high noise, bad linearity, and bad interference immunity. It applicable only for temperature sensor, if you need one. However, if you agree with 2-3% tolerance you can use it. But that case precision DC amplifier required.
Sigma-delta ADC is integrator, and many ADC`s have built-in filter(like ADS1251), and reject 50-60 Hz interferences thousand times.
2) I can help you with block diagram only if you give me technical parameters of the scale: precision, temperature range, display type (digit count) wire length (from sensor to ADC)
« Last Edit: September 03, 2008, 09:48:47 21:48 by Kwaigo » Logged
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