Strain Gauge
Aim:
Study of strain measurement using strain gauge and cantilever assembly.
Apparatus Required:
- Scientech 2304 kit
- Power supply
- Weights
- Connecting wires
Theory:
The strain gauge module consists of a cantilever beam which is fixed on a rigid body. The strain gauge which are fixed above the beam detects the longitudinal strain and fixed below the beam detects transversal strain.
When load is applied on the end of the beam a downward force is exerted. It tends to change the dimensions of the beam. The dimensional changes are sensed by the strain gauge fixed with the beam. The strain on the beam then calculated. The resistance of the strain gauge is changed due to the dimensional change in the beam when the load I applied. Due to this resistance change an unbalanced voltage is developed in the bridge output. This unbalanced voltage is further processed and calculated to give strain directly on the display.
Formula Used:
Strain = (6xFxL)/ (WxT2xY)
Where, F = mg
F= Force
m=mass
g=acceleration due to gravity
L=length = 20cm
T=thickness = 0.16cm
W=width = 2.5cm
Y=young’s modulus = 200×109 n/m2 for stainless steel
Procedure:
- Connect the hook on the cantilever beam and interface the connector with the kit.
- Nullify the bridge voltage/strain display by using zero adjust pot.
- Then apply the load and adjust the gain pot.
- Gradually increase the load by 50 gm. in the steps and note down the applied load on it.
Observation:
| Sr.No | Mass (gm.) | Practical strain (µ) | Theoretical strain (µ) | Error percentage |
| 1. | 50 | |||
| 2. | 100 | |||
| 3 | 150 | |||
| 4. | 200 | |||
| 5. | 250 | |||
| 6. | 300 | |||
| 7. | 350 | |||
| 8. | 400 |
Result:
The theoretical and practical value of strain is verified and its characteristics curve is also studied.
Precautions:
- Take the readings carefully.
- Initial strain before putting weights should be zero.
