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# Amplifying circuit for strain gages

Discussion in 'The Projects Forum' started by datran5, Mar 21, 2013.

1. ### datran5 Thread Starter New Member

Mar 21, 2013
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Hello,

I am currently working with 350-ohm strain gages (full bridge Wheatstone configuration) to make a load cell and need help building a circuit that will amplify the signal from the gages. I've made all the connections with the strain gages and have tested them out with a strain gage transducer amplifier. They are working fine, and are displaying good voltages. My goal now is to actually build an amplifying circuit using and AD524 op amp. I am a beginner with building circuits and need help getting started. Any insights, suggestions, or help will be greatly appreciated. Thank you.

Jul 9, 2011
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3. ### datran5 Thread Starter New Member

Mar 21, 2013
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Thank you for the quick reply. On the diagram, how is the 10kohm resistor (between pin 4 and 6) chosen? Also, what is the connection at pin 8 for? I'm not sure why the voltage source there is "connected" to that 10k resistor. I also do not have the ADC in the image. Is there another way to convert that voltage to an amplitude?

4. ### GopherT AAC Fanatic!

Nov 23, 2012
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The 10k resistor you mention is a potentiometer (adjustable voltage divider). The connection to pin 8 is the wiper of the 10k ohm potentiometer. This is used to null the output. That is, make sure it is zero at zero. You can adjust one leg of your bridge and test the balance with an ohm meter. However, the amplifier might not output that as a perfect zero. The null adjusts that offset.

5. ### datran5 Thread Starter New Member

Mar 21, 2013
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Let me try to understand that. The amplifier's output is offset (naturally?) so the 10k ohm potentiometer is connected to pin 8 (voltage source) to null that offset so that the output can be 0. This way the amplifier is more accurate. Because without nulling that offset, if we were to measure the output of the amp at 0, it wouldn't be 0, am I correct? You also mentioned changing one of the leg of the bridge and testing the balance. What do you mean by that?

6. ### DickCappels Moderator

Aug 21, 2008
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datran5 wrote:
"I also do not have the ADC in the image. Is there another way to convert that voltage to an amplitude?"

What do you mean by "amplitude"? You can measure the voltage with a voltmeter if you want.

7. ### datran5 Thread Starter New Member

Mar 21, 2013
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I just meant that I don't have an ADC. Ultimately, I want to connect this load cell to a computer so that I can record the forces I am applying on it. This means that I will need the ADC to convert the analog signal to a digital signal so that the computer can read it, is that correct?

**Thank you for all the help. I'm still a beginner in this field and appreciate all the helpful information