0.1 Temperature measurement and first-order dynamic response

Introduction:

In this lab exercise, you will determine how various temperature measurement systems respond to differentinputs. This analysis will include a thermometer, a thermocouple, and a thermistor.

Teaching objectives:

The purpose of this laboratory is for each student to understand and do the following:

1. Instrument calibration.

2. Measurements with thermocouples and thermistors.

3. Determination of time constants and comparisons of the dynamic responses of three measuringsystems.

4. Application of first-order dynamic behavior to dynamic temperature measurement problems.

Preparatory reading:

Figliola and Beasley

Measurement System Behavior, First Order Systems: pp. 72–87

Thermistors: p. 295

Thermoelectric Temperature Measurement: pp. 300-313

Overview:

In this lab, we will use first-order models to approximate the response of a thermometer, a thermocouple, and athermistor to temperature inputs. Each of these temperature sensors measure temperature in a different way.

• A thermometer senses a change in temperature as a change in the density of a fluid.
• A thermocouple consists of two wires of different metals joined at one end (the junction). When a voltage is applied acrossthe free ends of the two wires, the differing properties of the wires create an induced voltage that it proportional to thetemperature change at the junction.
• A thermistor is a thermally sensitive resistor. When the temperature of the thermistor changes, a proportional change inresistance occurs.

Procedure:

Part 1: modify a vi for temperature measurements

In this lab, we will build on the skills that were developed in Introduction to Benchtop Equipment and Data Acquisition . It is assumed that the student understands the concepts of a Front Panel, a Block Diagram, the ControlPalette, and the Functions Palette. It is also assumed that the student can search the control and functions palette for necessaryfeatures.

1. Connect a thermocouple to channel 0 of the SCXI-1112 module.

2. Open LabVIEW 8.0.

3. Open the VI that you developed for Introduction to Benchtop Equipment and Data Acquisition .

4. Click File>>Save As…>>Substitute Copy for Original to save your VI with a new name.

5. On the Block Diagram, double click the DAQ Assistant to open the configuration dialogue box.

6. Configure the DAQ Assistant as shown above.

• • Click Voltage and press Delete to delete the channel you used in the first lab.
  • A dialog box will ask if you want to delete the selected channel. Click Yes.
  • Add a new measurement channel.
    • Click Add Channels>>Voltage.
    • Select the channel that the thermocouple is connected to (SC1Mod2>>ai0).
    • Click OK.
  • The input range should be 80mV max to -80mV min. (Thermocouples have a low voltage output.)
  • The Terminal Configuration should be Differential. (The ground terminal is not used.)
  • Change Acquisition Mode to Continuous.
  • Click OK.
  • A dialog box will open asking if you would like a While Loop to be made around the DAQ Assistant. Click No. (You will place aWhile Loop in the next step that includes the subVIs that are already on the Block Diagram.