Campbell Scientific CR6 CR6 Measurement and Control System - Page 361
Vibrating-Wire Temperature Measurement
![]() |
View all Campbell Scientific CR6 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 361 highlights
Section 8. Operation Vibrating-Wire Temperature Measurement Temperature data from the two-wire RTD that is often embedded in vibratingwire sensors is used to correct measurement errors caused by thermal expansion and contraction of the sensor body. RTD resistance changes with sensor temperature. RTD leads connect to the U terminal pair numerically following the U terminal pair to which the vibrating-wire coil leads are connected. The RTD measurement is enabled in the VibratingWire() instruction with an argument other than zero in the ThermFnotch parameter . When the RTD measurement is made, the odd-numbered terminal of the pair applies excitation. An internal resistor is automatically switched into the circuit to complete the measurement bridge. For thermistor RTDs, temperature can be calculated automatically by inputing arguments other than 0 in the A, B, C parameters in the VibratingWire() instruction. The values to input are the Steinhart-Hart coefficients supplied by the sensor manufacturer. For sensors incorporating a PRT, inputing 0 as the argument for A, B, C will result in the output of resistance expressed as ohms. Converting Thermistor Resistance to Temperature The Steinhart-Hart equation is expressed as, T = 1 / (A + B • LN(R) + C • (LN(R))^3) - 273.15 Where T is the temperature of the thermistor, A, B, and C are coefficients, and R is the resistance of the thermistor. Note Coefficients for Steinhart-Hart are specific to the thermistor in the sensor. Obtain coefficients from the sensor manufacturer. For example, if the coefficients for Steinhart-Hart are provided from the manufacturer as follows, A = 1.4051E-03 B = 2.369E-04 C = 1.019E-07 the equation for converting the resistance measurement to degrees Celsius is: T = 1 / (1.4051E-03 + 2.369E-04 • LN(R) + 1.019E-7 • (LN(R))^3) - 273.15 Where R is the measured resistance. If the measured resistance is 2221 Ω, the equation is, T = 1/(1.4051E-03 + 2.369E-04 • LN(2221) + 1.019E-7 • (LN(2221))^3) - 273.15 T = 31.98 °C The CRBasic example Vspect Vibrating-Wire Measurement (p. 364) lists code that performs this conversion. Temperature-Measurement Error Accuracy of the temperature measurement is a function of: • Accuracy of the voltage measurement • Precision of the bridge resistors 361
![](/manual_guide/products/campbell-scientific-cr6-cr6-measurement-control-a476969/361.png)