How to connect this strain gauge?

[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