The Strain Application Adaptor is used for the teaching or demonstrating of PC Based Data Acquisition. Used with the EMANT300 Low Cost USB Data Acquisition Module, they form a very low cost PC based Strain Data Logger. It is ideal for use in hands-on teaching laboratories and projects involving strain measurements.
When an object is stretched due to an external force and the length of the object increases from L to L+ΔL, the ratio ΔL/L is called strain.
ε = ΔL/L
As the ratio of deformation is often very small, it is often represented in a units of 10-6 or μstrain
A strain gauge can be used to measure the strain of this object. The most common type of strain gauge consists of a flexible backing which supports a metallic foil pattern etched onto the backing. As the object is deformed, the foil pattern is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge circuit, can be used to calculate the exact amount of deformation by means of the quantity known as the gauge factor.
The gauge factor of a strain gauge relates strain to change in electrical resistance. The gauge factor GF is defined by the formula
where RG is the resistance of the undeformed gauge, ΔR is the change in resistance caused by strain, and ε is strain.
ΔR is typically in the region of 0.1%. To measure such small resistance changes, a Wheatstone bridge is employed. There are 3 configurations used - quarter bridge, half bridge or full bridge. The strain adaptor allows for all these three configurations by plugging in the respective bridge completion resistors and then wiring up the strain gauges via the screw terminals. Excitation voltage of 2.5V is provided. Up to six input channels are available.
Quarter Bridge Connection
Force sensors, pressure sensors and load cells that have a full bridge configuration and are ratiometric can also be connected to the strain application adaptor. You can connect up to 3 full bridge type sensors. For full bridges, no completion resistors are required.
Specification (PDF file size 370K)
Please use the Bridge Sensor Application Adaptor. Note the following differences between the strain application adaptor and the bridge sensor application adaptor: