# Still Confused: Strain Gauge interfacing

Discussion in 'General Electronics Chat' started by aamirali, Mar 26, 2014.

1. ### aamirali Thread Starter Member

Feb 2, 2012
415
1
Besides couple of threads I had started I have still some confusion regarding it.
I am rephrasing my query to make it more clear.

Figures may vary from previous thread & please correct me where I am wrong.

I have used a strain gauge with following specs:
Gauge factor = 2
Unstrained resistance = 1000ohm
max strain = 50000ue

I have attached the schematic.

1. I have connected 5V to wheatstone brigde & kept other three resistors as 1000ohm.

2. total percentage change in resistance = gauge factor * strain = 2*50000*10^-6 = 6%.
So total chnage in resistance = 60ohm.

3. I have connected a microcontroller to read the voltage. With 1 ohm change in strain gauge I read 1.249mV.

I don't know how I can calculate weight from it. There must be some mathematical realtionship between them.
How can I get with millivolts so much strain is produced or so muck kg of weight is applied.

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2. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,575
389
Usually a typical load cell bridge is rated at say 2mV signal per 1V of excitation, also the maximum weight is specified; 10Kg max, 2mV/V with say 5Vdc excitation 10mV out for 10Kg load.

Is this what you are asking.??

One way would be to use calibrated weights and a fixed Vx, say 5V or 10V and produce a graph of mV out versus weight

EDIT:

3. ### sirch2 Well-Known Member

Jan 21, 2013
1,008
351
What is the gauge attached to and how is it loaded (e.g. as a cantilever beam)? The relationship you are after depends on the Modulus of Elasticity of the material being loaded and how you load it.

4. ### t06afre AAC Fanatic!

May 11, 2009
5,939
1,222
Can you please tell us exactly what you are trying to do please!!!. Like what kind of setup do you have in mind. Feel more than welcome to use any illustration or photo. Before you do this it is hard to give propper help, or any other advice. It could be that your project is not viable. And in such case it is better to pull the plugg now and not later