How to connect this strain gauge?

[sophiecentaur]

4 * 120 ohm is the 480 ohm series resistor.
You must study the common mode input voltage range of the amplifier, to work out if the 120 ohm resistors should be placed above or below the bridge.

I was thinking that's the next stage in implementing. If the amp has + and - supplies then obvs the bridge should be hung between them so the common voltage would be around zero. But if single sided amp then the same thing applies but with half of the 480Ω above and half below. I was wondering if the OP will get this all in one go.

 

[sophiecentaur]

do i need to connect 480 ohm with these 4(120) ohm series resistors

They are not 'in series' on the bridge. They are in series / parallel - hence the 120 total.

 

[Micheal_Leo]

I was thinking that's the next stage in implementing. If the amp has + and - supplies then obvs the bridge should be hung between them so the common voltage would be around zero. But if single sided amp then the same thing applies but with half of the 480Ω above and half below. I was wondering if the OP will get this all in one go.

 

[Micheal_Leo]

They are not 'in series' on the bridge. They are in series / parallel - hence the 120 total.

please can you check like this , before attaching strain guage , the DMM show zero but when i attach strain gauge ( replacing one resistor in brdige with guage) it show 1.480V while beam is stationary

 

[sophiecentaur]

please can you check like this , before attaching strain guage , the DMM show zero but when i attach strain gauge ( replacing one resistor in brdige with guage) it show 1.480V while beam is stationary

what does that diagram mean? Look at other schematic diagrams. You will notice that connecting wires are actually joined together (often with a dot). Those 120Ω reasistors are not joined to anything so they don't "do" anything. You should try to stick to the conventions if you want to make sense. Have you seen a diagram of a bridge circuit? The power connects across one diagonal and the meter connects across the other diagonal. Your picture shows none of this.

PS the way you actually connect things together and where the wires go is best shown by a conventional circuit diagram. Your breadboard version means nothing to anyone else but you.

 

[sophiecentaur]

What should I understand from that picture? We don't seem to be getting anywhere with this at the moment.

 

[sophiecentaur]

We are talking in English and that's because we can rely (at least to some extent) on understanding what we both mean. I cannot converse with you is you don't use the equivalent convention when drawing diagrams. There is a universal standard for drawing circuits. You need to use it. It is not difficult. Just look at text books and serious web pages.

 

[Micheal_Leo]

what does that diagram mean? Look at other schematic diagrams. You will notice that connecting wires are actually joined together (often with a dot). Those 120Ω reasistors are not joined to anything so they don't "do" anything. You should try to stick to the conventions if you want to make sense. Have you seen a diagram of a bridge circuit? The power connects across one diagonal and the meter connects across the other diagonal. Your picture shows none of this.

PS the way you actually connect things together and where the wires go is best shown by a conventional circuit diagram. Your breadboard version means nothing to anyone else but you.

please fine the attached conventional diagram

 

[sophiecentaur]

Ahh!! I see what's wrong. The four strain gauge resistors ARE the bridge. No external 120Ω resistors are needed. (This is a great example of where one should start with a proper diagram; it can save a lot of wasted time.

 

[sophiecentaur]

The series resistor is used to reduce the 5V to 1V across the bridge supply.

 

[sophiecentaur]

I think you may have gottit!!!

 

[Micheal_Leo]

Ahh!! I see what's wrong. The four strain gauge resistors ARE the bridge. No external 120Ω resistors are needed. (This is a great example of where one should start with a proper diagram; it can save a lot of wasted time.

so should i make wheatstone bridge and connect this full strain bridge to it ? this is confusing that i should make a wheatstone bridge or not when these are full bridge strain gauge resistors

 

[sophiecentaur]

so should i make wheatstone bridge and connect this full strain bridge to it ? this is confusing that i should make a wheatstone bridge or not when these are full bridge strain gauge resistors

I thought you had got this. Why would you want another bridge when you have a strain gauge that IS a bridge? As the gauge flexes, resistors increase and decrease and the bridge becomes unbalanced proportionally with the strain. All you need is to reduce the supply volts to 1V by using the series resistor in the supply.

I suspect that you have not looked elsewhere to get an alternative view. there are dozens of web pages about the same problem. I cannot do the whole design job for. you.

 

[Micheal_Leo]

I thought you had got this. Why would you want another bridge when you have a strain gauge that IS a bridge? As the gauge flexes, resistors increase and decrease and the bridge becomes unbalanced proportionally with the strain. All you need is to reduce the supply volts to 1V by using the series resistor in the supply.

I suspect that you have not looked elsewhere to get an alternative view. there are dozens of web pages about the same problem. I cannot do the whole design job for. you.

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

 

[sophiecentaur]

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

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 that won't help you for next time.

 

[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