ET 150 Sensor Display Program LabVIEW Program 2

Transcription

1 ET 150 Sensor Display Program LabVIEW Program 2 Objective: Produce a display program that shows the temperature monitored by the LM34/35 integrated temperature transducer. The program should allow users to select the type of sensor connected to the monitoring PC and display the temperature in both degrees F and C. The program should record temperature measurements on a graph at two second intervals. Theoretical Background: LabVIEW is a graphical programming language that allows programmers to quickly construct displays and data analysis programs for engineering and scientific applications. The LabVIEW environment consists of a Measurement and Automation Explorer (MAX) program that provides software drivers that communicate with installed DAQ hardware and the LabVIEW language. LabVIEW users construct the front panel of data collection applications by dragging and dropping pre-defined interface objects to the screen and then interconnecting the objects using a signal wiring technique. Figure 1 shows a block diagram of the desired system for this lab activity. The signal LM34/35 Temperature Sensor Signal Amplifier DAQ Terminal Board Interface Cable LabVIEW Applications MAX Software DAQ Interface Card PCI 6221 or 6024E Software PC Hardware Figure 1. Data Acquisition System Overview. amplifier connects to the PC hardware through the DAQ terminal board. This board has 68 signal terminations for both analog and digital signals. This project will use an analog input. The pin diagram located in Appendix A of this handout shows the location of these pins on the terminal board. A 68 conductor cable connects the terminal board to the DAQ card installed in the PC located at each lab station. The installed card is either a National Instruments (NI) PCI 6221 or 6024E. The lab instructor will help you determine the exact hardware for your location. Fall Labview2.docx

2 The DAQ interface card converts external signals into compatible digital signals for further processing using the LabVIEW programming environment. Programmers define the types of inputs and can observe data channels before data processing using the MAX software. Finally, the analysis, scaling and display of senor data takes plan in the LabVIEW application. LabVIEW programs are called Virtual Instruments (VI) because they simulate the action of real test instruments and data recording devices in software. Procedure: 1.) View the demonstration videos on how to create programs using the LabVIEW programming environment. These demos show you exactly how to construct the program for this activity. 2.) Create the user interface shown in Figure 2. This interface consists of two digital Figure 2. Sensor Program Interface. indicator objects configured like thermometers for monitoring the temperature in both degrees F and C, a strip chart graph that displays the measurements as they are collected, a sensor selector switch, an amplifier gain input and a program stop button. Match the constructed interface to this figure. Fall Labview2.docx

3 3.) Switch to the back panel of the programming environment and connect the input/output variables to match Figure 3 and 3a. The measured voltages from the amplifier circuit enters the program at the DAQm Global Channel symbol Figure 3. Sensors Project Wiring Connections. through the analog input read function block. The signal is scaled by implementing Formula 1 from the previous lab using multiplication and division operations. This Figure 3a. Wiring For the False Case of the True/False Test. Fall Labview2.docx

4 equation is reproduced below. Formula 1 T A vm V out 0.010V/degree Where: T = Measured temperature V out = measured circuit output voltage A vm = measured circuit amplification factor The True/False (IF-Then-Else) block selects the proper scaling of the sensor output based on the user switch selection. Formulas 2 and 3 are the scaling equations for degrees F and C respectively. Formula 2 Formula 3 Where: C = temperature in degrees Centigrade F = temperature in degrees Fahrenheit The amplifier gain input must contain the proper value for correct scaling. (This value has theoretical values 11 and 4.3 for the LM35/LM34 respectively. Use the measured values of gain obtained for the R2 values of 100k and 33k ohms for your amplifier projects. The outputs from this decision block then go the display variables for Centigrade and Fahrenheit display. A WHILE-loop repeats this whole process until a user presses the stop button on the front panel. The WAIT function block delays the repetition of each loop execution for 2 seconds. 4.) Connect the output of the sensor and amplifier circuit to the DAQ terminal board using the connection diagram in the appendix. The amplifier output terminal should connect to pin ACH0 68 and the ground of the experimenter board connect to pin AIGND ) Run the program and check the displayed values for both degrees F and C. Record the values in Table 1 6.) Plug in a solder iron and let it come to a stable temperature. Bring the tip of the iron near, (approximately 1 inch), the temperature sensor. DO NOT TOUCH THE SENSOR WITH THE IRON TIP. 7.) Record the temperature measured in Table 1 at 1 minute intervals for 5 minutes. 8.) Unplug the iron and let it cool. Power down the temperature sensor circuit and stop the LabVIEW program. Fall Labview2.docx

5 Ambient Heat Applied 1 minute 2 minutes 3 minutes 4 minutes 5 minutes Table 1- Temperature Measurements Degrees F Degrees C Fall Labview2.docx

6 Appendix A DAQ Board Connection Diagram Fall Labview2.docx