Strain Gage Wiring System
A strain gage Wheatstone bridge is configured with a quarter, half, or full bridge according to the measuring purpose. The typical wiring systems are shown in Figs. 4,5 and 6.
Quarter-bridge system (1-gage system)
With the quarter-bridge system, a strain gage is connected to one leg of the bridge and a fixed resistor is connected to each of the other 3 legs. This system will be easily configured, and thus it is widely used for general stress or strain measurement. The quarter-bridge 2-wire system shown in Fig. 4 is largely affected by leads. Therefore, if a big temperature change is expected or if the lead-wire length is long, then the quarter-bridge 3-wire system shown in Fig. 4 must be used. For the quarter-bridge 3-wire system, See "Compensation Methods of Temperature Effect of Lead Wires".
Half-bridge system (2-gage system)
With the Half-bridge system, 2 strain gages are connected to the bridge, one each to adjacent or opposite legs with fixed resistors inserted in the other legs. See Figs. 5-1 and 5-2. There is the activedummy system, where one strain gage serves as a dummy gage for temperature compensation, and the active-active system, where both gages serve as active gages. The half-bridge system is used to eliminate strain components other than the target strain; according to the measuring purpose, 2 gages are connected to the bridge in different ways. For details, See "How to Form Strain-gage Bridge Circuits"
Full-bridge system (4-gage system)
See Fig. 6. The full-bridge system has 4 strain gages connected one each to all 4 legs of the bridge. This circuit ensures large output of strain-gage transducers, improves temperature compensation and eliminates strain components other than the target strain. For details, see "How to Form Strain-gage Bridge Circuits"