Specifications

Section 4. Sensor Support

4-19

EXAMPLE 4.3-1. CRBASIC Code: 4 Wire Full Bridge Measurement and Processing

'Declare Variables

Public X

Public X1

Public R1

Public R2

Public R3

Public R4

'Main Program

BeginProg

R2 = 1000 'Resistance of R2

R3 = 1000 'Resistance of R3

R4 = 1000 'Resistance of R4

Scan(500,mSec,1,0)

'Full Bridge measurement:

BrFull(X,1,mV2500,1,1,1,2500,True,True,0,_60Hz,1.0,0.0)

X1 = ((-1 * X) / 1000) + (R3 / (R3 + R4))

R1 = (R2 * (1 - X1)) / X1

NextScan

EndProg

4.3.1 Strain Calculations

Read more! FieldCalStrain in Section 11.1.6 FieldCalStrain()

Demonstration Program.

A principal use of the four wire full bridge is the measurement of strain gages

in structural stress analysis. StrainCalc() calculates microstrain, με, from an

appropriate formula for the particular strain bridge configuration used. All

strain gages supported by StrainCalc() use the full Wheatstone bridge

electronic configuration. In strain gage parlance, “quarter bridge”, “half

bridge” and “full bridge” refer to the number of active elements in the full

Wheatstone bridge, i.e., 1, 2, or 4 active elements respectively.

StrainCalc() requires a bridge configuration code. TABLE 4.3-1 shows the

equation i

nvoked by each configuration code. Each code can be preceded by a

negative sign (-). A positive code is employed when the bridge is configured

so the output decreases with increasing strain (compression). A negative code

is employed when the bridge is configured so the output increases with

increasing strain (tension). In the equations below, a negative code sets the

polarity of V

to negative (-).