How to connect this strain gauge?

[Micheal_Leo]

You can check this yourself, actually. Show the workings of how you came to this circuit. What would the R1 be and what would the R2 be? The resistance of the bridge will affect how things work, remember.
Note: I will not just give you the answer because

THe best R1=10000ohm and R2=2500 in this way i can get 1V from 5V power supply

 

[sophiecentaur]

THe best R1=10000ohm and R2=2500 in this way i can get 1V from 5V power supply

This is ridiculous. We've been here before. Just try it and see that you get much less than 1V because. you are loading the potential divider with 120Ω in parallel with your 2500Ω. You clearly don't want to learn about this; you just want me to post a diagram with full instructions about how to set it up. PF doesn't work that way. (At least, I don't.)

Come back when you can show that you understand about Potential Dividers.

 

[Baluncore]

... , please can you check this reducing the voltage to 1V conventional diagram

Not good.

THe best R1=10000ohm and R2=2500 in this way i can get 1V from 5V power supply

You are imagining a potentiometer, which will have a high output resistance = 2k, then shorting that with the 120R bridge.

If the bridge has elements of 120R, then the series resistance of each side is 240R, but there are two sides in parallel, which makes the whole bridge appear to be 120R.

Now you know that 120R will drop one volt.
If you need to eliminate 4 volts of the 5, you need four 120R resistors, in series with the bridge, carrying the same current.

 

[Micheal_Leo]

" If you need to eliminate 4 volts of the 5, you need four 120R resistors, in series with the bridge, carrying the same current"
this is very confusing , i have 120ohm fully strain guage resistors( 4 resistors in bridge) , i do not need external 120ohm resistors acting as wheatstone bridge till that point i understand , after that as you mentioned that " you need four 120R resistors, in series with the bridge" here bridge is fully strain gauge , than four 120ohm resistors where should i connect on breadboard

 

[Micheal_Leo]

This is ridiculous. We've been here before. Just try it and see that you get much less than 1V because. you are loading the potential divider with 120Ω in parallel with your 2500Ω. You clearly don't want to learn about this; you just want me to post a diagram with full instructions about how to set it up. PF doesn't work that way. (At least, I don't.)

Come back when you can show that you understand about Potential Dividers.

i am trying best to understand it

 

[Baluncore]

i am trying best to understand it

You are way out of your depth.
Study ohms law.

 

[sophiecentaur]

i do not need external 120ohm resistors acting as wheatstone bridge

What you need is 480Ω. It is a complete coincidence that you happen to have four 120Ω resistors and that they will give you 480Ω when connected in series. You should try to work out how you would get 1V if your supply volts were 6V - just one resistor is needed.

i am trying best to understand it

I think you are trying to get as much help as possible without actually learning anything. What is your level of Electronics / Science qualification? I assume that you want to do some mechanics measurements using electronics without actually learning the electronics. your only option, afaics, is to buy a working strain gauge unit and fix it to your mechanics experiment. If that would be too costly then choose a different mechanics project.

 

[Micheal_Leo]

What you need is 480Ω. It is a complete coincidence that you happen to have four 120Ω resistors and that they will give you 480Ω when connected in series. You should try to work out how you would get 1V if your supply volts were 6V - just one resistor is needed.

I think you are trying to get as much help as possible without actually learning anything. What is your level of Electronics / Science qualification? I assume that you want to do some mechanics measurements using electronics without actually learning the electronics. your only option, afaics, is to buy a working strain gauge unit and fix it to your mechanics experiment. If that would be too costly then choose a different mechanics project.

Voltage Source (VS) = 6V
Volts (V) = 1V( needed)
Resistance 1 (R1) = 480
Resistance 2 (R2) = 96
R2 should be 96 ohm to have 1V output

specifically voltage divider

i am learning from deep heart and thinking , today learn so many things , sometime get stuck

 

[sophiecentaur]

R2 should be 96 ohm to have 1V output

Alternatively, what R1 would you need so that you could just use the 120Ω for R2. Just re-arrange the equation to find the single resistor that can be used for R1. Certainly not 480Ω.

 

[Micheal_Leo]

Alternatively, what R1 would you need so that you could just use the 120Ω for R2. Just re-arrange the equation to find the single resistor that can be used for R1. Certainly not 480Ω.

after rearranging
R1= (Vin-Vout)R2 / Vout
IF Vin=5
Vin=5
R2=120
Vout=1
So R1=480 ohm
i always getting 480

 

[sophiecentaur]

i always getting 480

OMG - such a scatterbrain. That's not surprising if you started with 5 volts. My question was about starting with 6V.

 

[Micheal_Leo]

OMG - such a scatterbrain. That's not surprising if you started with 5 volts. My question was about starting with 6V.

If Vin=6
R1= (Vin-Vout)R2 / Vout
R2=120
Vout=1
So R1=600 ohm

 

[sophiecentaur]

That’s better. I could believe that. So you learned a lesson about ‘garbage in garbage out’.
So build it and draw a proper diagram of your circuit. See what Arduino does now.

 

[Micheal_Leo]

That’s better. I could believe that. So you learned a lesson about ‘garbage in garbage out’.
So build it and draw a proper diagram of your circuit. See what Arduino does now.

so i do not have 600 full ( i have 510+100) , the circuit given below

 

[sophiecentaur]

so i do not have 600 full ( i have 510+100) , the circuit given below

This is a very common situation for a home experimenter. The 'wanted' 1V is not critical so whatever you get will be 'near enough for Jazz' as long as you got your sums right.

 

[Micheal_Leo]

This is a very common situation for a home experimenter. The 'wanted' 1V is not critical so whatever you get will be 'near enough for Jazz' as long as you got your sums right.

so the circuit is good ?

 

[sophiecentaur]

so the circuit is good ?

I have no idea what that wiring picture is about. You have TWO power supplies??? Why don't you get used to drawing a proper conventional circuit diagram with straight lines, right angled bends when needed - Just like the ones you can see everywhere else?
Remember what I told you about speaking English. So Speak proper circuit diagrams. Practice and look at the millions you can find on the net.

 

[Micheal_Leo]

I have no idea what that wiring picture is about. You have TWO power supplies??? Why don't you get used to drawing a proper conventional circuit diagram with straight lines, right angled bends when needed - Just like the ones you can see everywhere else?
Remember what I told you about speaking English. So Speak proper circuit diagrams. Practice and look at the millions you can find on the net.

yes i have two power supplies , one for AD620 and one for strain gauge ,

 

[Baluncore]

Why do you have 6 volt supply for AD620?
Can you not use 5 volts for AD620 and Bridge supply?

 

[Micheal_Leo]

Why do you have 6 volt supply for AD620?
Can you not use 5 volts for AD620 and Bridge supply?

i have supplied 5v to both strain guage and AD620 , however while measuring output from AD620 , mV values fluctuates a lot , even the beam not bend

DMM output reading from AD620

 

[Baluncore]

i have supplied 5v to both strain guage and AD620 , however while measuring output from AD620 , mV values fluctuates a lot , ...

Maybe that is because you have not met the common mode input requirements of the AD620. At the bottom of page 3, of the AD620 data sheet, is shown the common mode input voltage range.
I list the input design voltages in order, for a supply of +5 V.
The order of computation is 1, 2, 3, 4.

1. Vp = +5 V. Positive power supply.
2. Vp – 1.4 V = 3.6 V. Maximum AD620 CM input voltage.
4. Voltage at top of bridge = 3.35 V; ( 5.0 - 3.35 ) * 120Ω = 198 ohms.
3. Vin midpoint = ( 2.1 + 3.6 ) / 2 = 2.85 V = ideal S+ and S- voltages.
4. Voltage at bottom of bridge = 2.35 V; 2.35 * 120Ω = 282 ohms.
2. Vn + 2.1V = 2.1 V. Minimum AD620 CM input voltage.
1. Vn = 0 V. Negative power supply.

Check: 198Ω + 282Ω = 480Ω = 120Ω x 4 = 4 volts dropped external to the bridge.
So the resistors to use will be:
From Vp to top of bridge use = 100Ω + 100Ω = 200Ω.
From Vn to bottom of bridge use = 100Ω + 180Ω = 280Ω.

 

[Micheal_Leo]

Maybe that is because you have not met the common mode input requirements of the AD620. At the bottom of page 3, of the AD620 data sheet, is shown the common mode input voltage range.
I list the input design voltages in order, for a supply of +5 V.
The order of computation is 1, 2, 3, 4.

1. Vp = +5 V. Positive power supply.
2. Vp – 1.4 V = 3.6 V. Maximum AD620 CM input voltage.
4. Voltage at top of bridge = 3.35 V; ( 5.0 - 3.35 ) * 120Ω = 198 ohms.
3. Vin midpoint = ( 2.1 + 3.6 ) / 2 = 2.85 V = ideal S+ and S- voltages.
4. Voltage at bottom of bridge = 2.35 V; 2.35 * 120Ω = 282 ohms.
2. Vn + 2.1V = 2.1 V. Minimum AD620 CM input voltage.
1. Vn = 0 V. Negative power supply.

Check: 198Ω + 282Ω = 480Ω = 120Ω x 4 = 4 volts dropped external to the bridge.
So the resistors to use will be:
From Vp to top of bridge use = 100Ω + 100Ω = 200Ω.
From Vn to bottom of bridge use = 100Ω + 180Ω = 280Ω.

just did experiment that i remove AD620 and connect DMM with S+ and S+ of strain gauge , mv fluctuates a lot while beam not bend

 

[Baluncore]

just did experiment that i remove AD620 and connect DMM with S+ and S+ , mv fluctuates a lot

Then you have bad connections, or a crack in the strain gauge trace.

 

[Tom.G]

Then you have bad connections, or a crack in the strain gauge trace.

Or a noisy power supply.
Or maybe you have a finger on a meter probe - or on a wire.
Or maybe you have long wires that pick up electrical noise from a close radio or TV transmitter - or from a fluorescent or LED light.

Please try it with the power supply turned Off but Everything else the same.

Cheers,
Tom

 

[Micheal_Leo]

Or a noisy power supply.
Or maybe you have a finger on a meter probe - or on a wire.
Or maybe you have long wires that pick up electrical noise from a close radio or TV transmitter - or from a fluorescent or LED light.

Please try it with the power supply turned Off but Everything else the same.

Cheers,
Tom

i turn off power supply to guage and Ad620 , the DMM values jumping goes to -400 and more

 

[Micheal_Leo]

Or a noisy power supply.
Or maybe you have a finger on a meter probe - or on a wire.
Or maybe you have long wires that pick up electrical noise from a close radio or TV transmitter - or from a fluorescent or LED light.

Please try it with the power supply turned Off but Everything else the same.

Cheers

i have successfully tested DMM by paste one linear strain guage at beam, some assumptions has been made however the DMM is good, i am doubt for my strain gauge there is something wrong in my circuit.
i beleive this strain guage that i have posted not.getting any current or may be strain gauge below some cut connections , so confused
attached video

video tested DMM

 

[Baluncore]

i beleive this strain guage that i have posted not.getting any current or may be strain gauge below some cut connections , so confused

Make four good wire connections to a strain gauge bridge.
Measure the resistance of the gauge with a DMM.

For a bridge made from four 120 Ω elements.
P+ to P-, and S+ to S- should measure a stable 120 Ω.
Any P, to any S, should measure a stable 90 Ω.

To detect broken elements, flex the bridge while measuring resistance. If you see 360 Ω, in place of 90 Ω, the element you are measuring is open circuit. If you see 240 Ω, in place of 120 Ω, there is a faulty element.

 

[Micheal_Leo]

Make four good wire connections to a strain gauge bridge.
Measure the resistance of the gauge with a DMM.

For a bridge made from four 120 Ω elements.
P+ to P-, and S+ to S- should measure a stable 120 Ω.
Any P, to any S, should measure a stable 90 Ω.

To detect broken elements, flex the bridge while measuring resistance. If you see 360 Ω, in place of 90 Ω, the element you are measuring is open circuit. If you see 240 Ω, in place of 120 Ω, there is a faulty element.

thank you very much going to try this