# Will strain resistance will go up

Discussion in 'General Electronics Chat' started by aamirali, Aug 8, 2014.

1. ### aamirali Thread Starter Member

Feb 2, 2012
415
2
I have a strain gauge of 1000ohm, with 50000 microstarin & GF=2 it can exhibit a change of 100ohms.

Do strain resistance value will always go down i.e 1000-100 = 900ohms.
or it can go above 1000 ohms. Like 1000+100 = 1100ohms

2. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
519
The behaviour depends upon the nature of the strain and the material of the sensor.

Firstly the mechanical nature.

For most materials if they are strained in tension their cross section will decrease and their length increase, whilst their resistivity remains sensible constant so the resistance goes up.

This applies to Nichrome, Constantin, Advance, Isoelastic, Karma, Manganin, Platinum-Iridium, Monel and Platinum.
For all these the gauge Factor (GF) is positive.
It is 2 for Nichrome and Constantin.

The odd one out is nickel which has a large negative GF (-12) so the resistance will go down.

However if a gauge is bonded onto the substrate in the pre-strained condition and released, then a contraction will occur and the positions are reversed.

3. ### aamirali Thread Starter Member

Feb 2, 2012
415
2
@studiot,

1. I am using strain gauge from vishay whose datasheet i have attached.

2. I know that in compression resistance decrease & vice versa.

3. But in datasheet it says only, strain range = 5%. For gf = 2 & R = 1K, total change in resistance will be 100ohms.

Now does that resistance will go 100 ohm down(i.e 900ohm) in case of compression
& in case of tension it will go up 100 ohm (i.e 1100 ohm) to show maximum strain i.e
5% or 50000 microstrain

This is what i am asking?

4. ### aamirali Thread Starter Member

Feb 2, 2012
415
2
edit: strain datasheet:

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5. ### paulktreg Distinguished Member

Jun 2, 2008
666
135
The strain range is plus or minus 5% so perhaps it can go to 1100R and down to 900R depending on which way it is "bent"?