Strain-gage Wiring Systems
A strain gage Wheatstone bridge is configured with1, 2 or 4 gages according to the measuring purpose.The typical wiring systems are shown in Figs. 4,5 and 6.
With the 1-gage system, a strain gage is connectedto one side of the bridge and a fixed resistor isconnected to each of the other 3 sides. This systemcan easily be configured, and thus it is widely usedfor general stress/strain measurement. The 1-gage2-wire system shown in Fig. 4-1 is largely affectedby leads. Therefore, if large temperature changesare anticipated or if the lead wire length is long, thenthe 1-gage 3-wire system shown in Fig. 4-2 must beused. For the 1-gage 3-wire system, refer to “Methodof Compensating Temperature Effect of Leadwire”
With the 2-gage system, 2 strain gages are connected to the bridge, one each to adjacent or opposite sides withfixed resistor inserted in the other sides. See Figs. 5-1and 5-2 . There exist the active-dummy method, whereone strain gage serves as a dummy gage for temperaturecompensation, and the active-active method, whereboth gages serve as active gages. The 2-gage system isused to eliminate strain components other than the targetstrain; according to the measuring purpose, 2 gages areconnected to the bridge in different ways. For details,refer to “How to Form Strain Gage Bridges”
See Fig. 6. The 4-gage system has 4 strain gagesconnected one each to all 4 sides of the bridge.This circuit ensures large output of strain gagetransducers and improves temperature compensationas well as eliminates strain components other thanthe target strain. For details, refer to “How to FormStrain Gage Bridges”