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How to connect this strain gauge?

kusspuss

Aug 25, 2023
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I would run the strain gauge off 5V, the AD620 off 9V. That would put
40 mA thru strain gauge, what was the max allowed current ?

If thats too much current power off 9V with a series R to limit current
to spec.


Regards, Dana.
max current is 25mA
 

kusspuss

Aug 25, 2023
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I would run the strain gauge off 5V, the AD620 off 9V. That would put
40 mA thru strain gauge, what was the max allowed current ?

If thats too much current power off 9V with a series R to limit current
to spec. Or use a low voltage zener. This all has to be simed out to see
what range you get into A/D. Ideally A/D would see 0 - 5V or something
like that. Depends on how unbalanced the starin gauge is in application.

Is your Arduino running off 3.3 or 5V ?


Regards, Dana.
i have arduino mega 2560 , which is 5V
 

danadak

Feb 19, 2021
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Feb 19, 2021
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768
i am not sure i can find or not here , but the values are jumping a lot , never stable , please need your guide to solve this jumping values

this device?

Currently what is the AD620 G set at ?
 

danadak

Feb 19, 2021
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So I would run the strain gauge off 5V with a series R of 120 ohms to its
+ power lead. Thats 20 mA thru bridge. Then use diamond tool to find
what Vref you need and G setting for 620 to get 0 - 5V out of it. For a +100
mV deviation in the bridge and 0V for a -100 mV deviation.
 

danadak

Feb 19, 2021
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Great scope, so in display mode set it to AC, 1V / div, infinte persistence, sweep
rate of say 1 mS / div, norm trigegring, trigegr set to edge, say 50 mV, and what do
you get for peak to peak noise. Let it run in that mode for a minute or two before
you take the visual reading.
 

danadak

Feb 19, 2021
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You need to set the G, not with a pot, but a fixed R. So we have
a design deviation of +/- 100 mV, and we want the slope of a straight
line into A/D, when at +100 mV, to generate 5V. So what is that G ?
 

danadak

Feb 19, 2021
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Remember to add a R between A/D input and AD620 / last opamp
you are using to prevent overdriving A/D input and damaging it. Say for
now 1K to 2K.

What does your schematic look like now ?
 

kusspuss

Aug 25, 2023
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Remember to add a R between A/D input and AD620 / last opamp
you are using to prevent overdriving A/D input and damaging it. Say for
now 1K to 2K.

What does your schematic look like now ?
right now i have done this , but not satisfied output , i see my one AD620 burn today , please need your more guidance
 

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danadak

Feb 19, 2021
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768
Remember you are working with a straight line transfer function with an offset.
These settings interact with each other. But we know how to fix the G, discussed
above, now we have to get the offset right.

I am going to leave for awhile, get a pic of your power supply adapter output.
Many of those crappy supplies have a minimum load requirement to stay in
regulation and keep noise down. So examine it with scope.

You want a clean, low noise, say 100 mV or less out of it, and ~ the value you
are seeking.
 

kusspuss

Aug 25, 2023
32
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Remember to add a R between A/D input and AD620 / last opamp
you are using to prevent overdriving A/D input and damaging it. Say for
now 1K to 2K.

What does your schematic look like now ?
just did experiment that i remove AD620 and connect DMM with S+ and S+ of strain gauge , mv fluctuates a lot
 

kusspuss

Aug 25, 2023
32
Joined
Aug 25, 2023
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Remember you are working with a straight line transfer function with an offset.
These settings interact with each other. But we know how to fix the G, discussed
above, now we have to get the offset right.

I am going to leave for awhile, get a pic of your power supply adapter output.
Many of those crappy supplies have a minimum load requirement to stay in
regulation and keep noise down. So examine it with scope.

You want a clean, low noise, say 100 mV or less out of it, and ~ the value you
are seeking.
yes output expected as < 100mv to arduino from strain gauge at condition of beam bending
 

danadak

Feb 19, 2021
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768
What does you schematic look like now.

Your DMM, just the LSD flickering ? Battery good in DMM ?


Regards, Dana.
 

danadak

Feb 19, 2021
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I did a sim, but AD620 spice model has a problem allowing a connection
to Vref pin. So I have contacted Analog Devices to see if I can get this
rectified.

1693178218247.png


Basically R2 is swept from 120 to 140 ohms.


Regards, Dana.
 
Last edited:

kusspuss

Aug 25, 2023
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What does you schematic look like now.

Your DMM, just the LSD flickering ? Battery good in DMM ?


Regards, Dana.
this is my schematic daigram, battery is good i believe
 

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kusspuss

Aug 25, 2023
32
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Aug 25, 2023
Messages
32
Remember to add a R between A/D input and AD620 / last opamp
you are using to prevent overdriving A/D input and damaging it. Say for
now 1K to 2K.

What does your schematic look like now ?
please how can i add resistor to prevent from damage, as before my Ad620 heatup
 

danadak

Feb 19, 2021
768
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768
The module has output V that you connect to Arduino A/D. Simple insert a R in series
with that connection.

AD620 module output >> R >> Arduino A/D input pin.


Regards, Dana.
 

danadak

Feb 19, 2021
768
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768
so the module i have not work properly

Do a simple test, no arduino, just module and a small V into module inputs :

1693226693072.png

Replace above probe with your module inputs, and set its G to 10, and use
the diamond tool to predict, for the Vref you have, what output should be,
and compare that with what the test gives you.

The V above is ~ 122 mV. Note the CM V is ~ 2.5V


Regards, Dana.
 
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