0.1 Temperature measurement and first-order dynamic response  (Page 2/5)

7. Place a While Loop around the entire Block Diagram as shown below. LabVIEW While Loops are similar to WhileLoops in any text-based programming language. The routine inside the loop will run repeatedly until a true value is passed to theloop condition, represented by a red button at the bottom right corner of the loop.

8. A toggle button can be used to end the While Loop routine. Right click on the loop condition icon andclick Create>>Control.

9. Double click the Write to Measurement File ExpressVI to open the configuration box. Under If a file alreadyexists, select Append to File. Click OK. (Because the Write to File function now occurs in a loop, the data must be appended to the endof the file, rather than overwriting the data from the previous loop.)

10. On the front panel, place a Thermometer.

11. Right Click the Thermometer. Click Visible Items>>Digital Display.

12. On the Block Diagram, inside the While Loop, place a Time Delay Express VI. When the Configuration Boxopens, change the Time Delay (seconds) to 0.001. (Without a delay in the While Loop, the program will repeat as quickly as it can andconsume processor power.)

13. Your Block Diagram should resemble Figure 3.

14. Click File>>Save As…>>Copy>>Create Unopened Disk Copy. Save the VI with“Lab3”in the file name. (You will use the VI as it is now as a starting point in Operational Amplifiers and Signal Conditioning .)

15. Save a second copy with“Lab4”in the file name. (You will also use the VI as it is now as astarting point in Strain Gages and Force Measurement .)

Part 2: calibration curve

You will create a static calibration curve tocorrelate voltage measurements with temperature readings. We will use the thermometer as the standard. (Note: We use the thermometeras a standard for convenience. Do not assume that an alcohol-in-glass thermometer is a temperature measurement devicewith superior accuracy.)

2.1 calibrate the thermocouple

1. Take temperature readings with the thermometer in ice water and boiling water. Be careful not to allowthe devices to come into contact with the hot plate or the bottom of the beaker.

2. Record the temperatures measured.

3. Use the thermocouple to measure both temperatures. Again, be careful not to allow the devices to come incontact with the hot plate or the bottom of the beaker.

4. In Excel:

• • Plot the temperatures measured with the known standard values on the y-axis and the ADC output (voltage) resulting from thethermocouple input on the x-axis.
  • Create a linear curve fit using the two data points.

The linear fit results in an equation that relates the ADC output obtained from the thermocouple to the knowntemperature from the thermometer:

T=k(Vadc) + b

where“T”is the temperature,“k”is the gain (°C/V),“Vadc”is the voltage read in to the computer, and“b”is the zero-voltage offset. The gain“k”is the inverse of the static sensitivity, which has units of V/°C.

5. Repeat the calibration procedure for the thermistor.

2.2 modify your vi for calibration