# Still Confused: Strain Gauge interfacing

#### aamirali

Joined Feb 2, 2012
412
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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#### ericgibbs

Joined Jan 29, 2010
19,071
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:
Your posted diagram is too small to read..

#### sirch2

Joined Jan 21, 2013
1,037
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.

#### t06afre

Joined May 11, 2009
5,934
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.
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