Campbell CR310 - RTD and PRT; Strain Measurements

CRBasic Example 1: Four-wire full-bridge measurement and processing
Public X_1
Public R_1
Public R_2 = 1000 'Resistance of fixed resistor R2
Public R_3 = 1000 'Resistance of fixed resistor R3
Public R_4 = 1000 'Resistance of fixed resistor R4
'Main Program
BeginProg
Scan(500,mSec,1,0)
'Full Bridge Measurement:
BrFull(X,1,mV2500,1,Vx1,1,2500,False,True,0,60,1.0,0.0)
X_1 = ((-1 * X) / 1000) + (R_3 / (R_3 + R_4))
R_1 = (R_2 * (1 - X_1)) / X_1
NextScan
EndProg
18.3.2 RTD and PRT
RTDs (resistance temperature detectors) are resistive devices made of platinum, nickel, copper,
or other material. Platinum RTDs, known as PRTs (platinum resistance thermometers) are very
accurate temperature measurement sensors.
A PRT element is a specialized resistor with two connection points. Most PRTs are either 100Ω or
1000Ω. This number is the resistance the PRT has at 0°C. The resistance of a PRT increases as it is
warmed. Industry standards define how PRTs respond to temperature.
BrHalf4W() in combination with PRTCalc() are the recommended CRBasic instructions for
measuring RTDs.
See the CRBasic Editor help for detailed instruction information and program examples:
https://help.campbellsci.com/crbasic/cr300/ .
18.3.3 Strain measurements
A principal use of the four-wire full bridge is the measurement of strain gages in structural stress
analysis. StrainCalc() calculates microstrain (µɛ) from the formula for the specific bridge
configuration used. All strain gages supported by StrainCalc() use the full-bridge schematic.
'Quarter-bridge', 'half-bridge' and 'full-bridge' refer to the number of active elements in the
bridge schematic. In other words, a quarter-bridge strain gage has one active element, a half-
bridge has two, and a full-bridge has four.
StrainCalc() requires a bridge-configuration code. The following table shows the equation
used by each configuration code. Each code can be preceded by a dash (-). Use a code without
18. Measurements98