Wheatstone power

[bee]

Hi

I have a wheatstone bridge circuit reading a change in resistance of a strain gauge through op amp working fine but need to reduce power while keeping the circuit working
resistors 120ohms s/gauge 120ohms voltage 5volts i am not an expert

any help thanks

 

[Roff]

Hi

I have a wheatstone bridge circuit reading a change in resistance of a strain gauge through op amp working fine but need to reduce power while keeping the circuit working
resistors 120ohms s/gauge 120ohms voltage 5volts i am not an expert

any help thanks

You can cut the power dissipated by the bridge almost in half by changing two of the resistors to a higher value.
The strain gauge is in series with one of the 120Ω resistors. That can't change. The other two can be much higher. Their actual value is not critical as long as they are equal, both have the same temperature coefficient, and are in a common thermal environment. They do need to be low enough value that amplifier bias current is not a factor. What kind of amplifier are you using, and what is the gain?

 

[bee]

The op amp is a mcp6292 microchip and the gain is 100
the res into op amp are 100k + side and 1k - side and 1meg feedback
thanks

 

[ericgibbs]

Hi

I have a wheatstone bridge circuit reading a change in resistance of a strain gauge through op amp working fine but need to reduce power while keeping the circuit working
resistors 120ohms s/gauge 120ohms voltage 5volts i am not an expert

any help thanks

hi,
If you reduce the 'power' to the bridge, I assume you mean the bridge excitation voltage.[Vx]?

If you reduce the Vx to the bridge you will reduce the sensistivity and 'span' of the bridge also.
This means for example of you halved the Vx you would have to double the gain of the op amp
in order to keep the range and calibration.

Strain gauge bridges a specified as mV[Output] per Volts[Vx]

 

[bee]

i have changed the the two resistors not in series with the gauge to a higher value and the current is reduced will play around some more tomorrow
thanks for the replies

 

[Roff]

The op amp is a mcp6292 microchip and the gain is 100
the res into op amp are 100k + side and 1k - side and 1meg bias
thanks

I assumed you were using an instrumentation amp.
You need to post a schematic. My suggestion may not work with your existing circuit.

 

[bee]

hi
I dont have a schematic drawing yet on the computer .The op amp is a rail to rail amp thanks for your suggestion it already works increased resistors from 120 to 270 and it has dropped from 32ma to around 20ma much better. Dont know how far i can go yet with the resistors. Dont have much time at the moment to play around with it so a bit slow to post
thanks
bee

 

[Roff]

hi
I dont have a schematic drawing yet on the computer .The op amp is a rail to rail amp thanks for your suggestion it already works increased resistors from 120 to 270 and it has dropped from 32ma to around 20ma much better. Dont know how far i can go yet with the resistors. Dont have much time at the moment to play around with it so a bit slow to post
thanks
bee

With an instrumentation amp, you could make the other leg out of 10k resistors, reducing the bridge current from about42mA to about 21mA.
I'm curious how you got only 32mA with a 5V supply and a bridge with four 120 ohm resistors. 32mA would be the result of a bridge with four 156.25 ohm resistors.

 

[bee]

hi
I have two res at 270 one side of bridge then the other side of bridge is 120 then s/gauge at 120 if that works out ? all i know is it worked I havnt done the maths regards bee