Lab 4_TemperatureCal

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Temperature Calibration Lab - 1 - ME310 – Instrumentation and Theory of Experiments Lab 4: Temperature Calibration and Measurement CONCEPTS: temperature measurements, RTDs, thermistors, digital data acquisition, LabVIEW GUIs DELIVERABLES: Full lab report ( with full uncertainty analysis) document, due in 2 weeks, in lab. 1. Introduction Two important aspects of temperature measurement are choosing the measurement device and obtaining an accurate calibration. Different devices, such as thermistors and resistance temperature detectors each offer advantages and disadvantages in measuring temperature, in the response time and the response function, as well as variations between the many different types of each device that are available. Choosing the appropriate instrument can be a significant factor in obtaining valid results. Equally important is the ability to accurately determine the temperature being measured. Each of the devices mentioned above measures changes in properties other than temperature that can in turn be related to a change in temperature. To measure temperature effectively, an accurate calibration is necessary between the change in properties actually measured and the associated change in temperature. In this lab you will use constant temperature baths to investigate variations in the capabilities and properties of two different temperature measurement devices. You will also calibrate each of the three devices using physical ice points. 2. Theory Thermistors and resistance temperature detectors (RTDs) measure properties that can be used to determine the temperature of a substance. Whereas thermocouples (discussed in class) use as their thermometric property the voltage that is created between two different metals when two bimetal junctions are at different temperatures, RTDs and thermistors use the fact that as temperature changes, the electrical resistance of materials change (thermistor = thermal + resistor…). In the sections that follow each of these devices is explained briefly.

Temperature Calibration Lab - 2 - 2.1. Thermistors & RTDs As mentioned above, thermistors and RTDs rely on the fact that the resistivity of a substance changes as its temperature does. The main difference between thermistors and RTD’s is the material from which they are made. Another difference (actually a function of the material and the implementation) is that the response of an RTD is more linear than a thermistor, while the thermistor is more sensitive. RTDs are generally made of a conductive metal. In a conductor the atoms can be thought of being in a regular lattice. The metal’s conduction properties are a result of the lattice: an irregular lattice is a poor conductor compared to a more regular one. As temperature increases the atoms in the lattice shake more, making it more irregular, thus scattering more of the conduction electrons, not allowing them to conduct current. The decrease in the ability to conduct current is seen as an increase in the metal’s resistivity. The response of the resistance R to the sensed temperature T can be approximated to be a function of the empirical fit coefficients a , R 0 , and T 0 : R ≈ R 0 [1 + a ( T-T 0 )] Thermistors are generally made from a semi-conducting material, such as a ceramic material. Semiconductors are characterized by having two energy bands (in their electron cloud) separated by an energy gap. The band with a lower energy is called the valence band, while the band with higher energy is called the conduction band. The population of the conduction band of a semi-conductor determines its resistivity. Electrons from the valence band can jump to the conduction band, across the energy gap, if they acquire enough energy. Energy can be added to electrons in the valence band by increasing the temperature. As temperature increases, resistivity goes down, because the population of the conduction band increases. The response of the resistance R to the sensed temperature T can be approximated to be a function of the empirical fit coefficients b , R 0 , and T 0 : R ≈ R 0 exp[ b (1/ T-1/T 0 ) ] RTDs have a relatively slow response time. With this in mind, they are not usually used for applications in which the temperature varies quickly. Thermistors have a relatively quick response time, and are not as delicate as RTDs, so they can be used in applications that have harsh environmental conditions. Thermistors can be easily packaged in a manner that will allow them to be flat mounted to a device. The use of these devices relies on a calibration of the device, usually obtained by measuring the output of the system as the temperature is varied in a known controlled fashion. Note that the data sheets for the RTD and thermistor that you’ll use in lab isn’t available because the goal of this lab is to determine the entire sensing system’s response through its calibration. Prelab question : Research and summarize two commercial systems that incorporate each device (4 systems total).

Temperature Calibration Lab - 3 - 3. Procedure NOTE: Each student should transfer the data files from the computer, either via transfer to the cloud or your own USB drive. Before beginning the lab, be certain you can identify thermistor and RTD devices. A pdf of both instruments can be found on the course website, since they look similar in appearance. Spot check thought questions: Read through & think about the questions in Section 5. 3.1. Data Acquisition This lab uses a National Instruments BNC-2090 breakout box connected to the National Instruments PCI-6221 data acquisition board (the same board as lab 3 and the design project) using a 64-pin I/O cable. The input range that the board is set via the LabView VI. Double-check with the GST that it is set to ±10 V. Constant Temperature Baths Portions of this section may already be in progress at the time you start your lab. Check with the GST to determine the state of each temperature bath. Set the temperature of the five temperature baths as follows: 1. Fill the 0ºC bath approximately 50% full from a cold water tap and add ice as necessary. 2. Fill the 15ºC bath to approximately 70% of capacity from a cold water tap and add ice as necessary until the temperature drops slightly below 15ºC. Allow the temperature to slowly rise to 15ºC. Once at 15ºC, continue to monitor the temperature and add ice as necessary to maintain that temperature. 3. Fill the 30ºC bath from a cold water tap. Allow 30-45 min. for the water to reach 30ºC with the aid of the immersion heaters. 4. Fill the 45ºC and 60ºC from a hot water tap. Allow 30-45 min. for the water to reach the proper temperature with the aid of the immersion heaters. The immersion heaters draw a lot of current and may cause a ground loop in the form of the 60-Hz AC voltage in conjunction with the rest of the measurement devices. Since the water isn’t deionized, the sensors (thermistors and RTDs), which act as antennas, can pick up this signal and disrupt their voltage output that you’re seeking to measure. Observe the signals on an oscilloscope to identify the different types of noise in the signals. Identify the different noise sources in the system if possible. Employ instrument level filtering provided in the lab such as the Krohn-Hite Model 3940 filter to remove the noise. A DC-coupled lowpass filter with a cutoff frequency of 50 Hz should be sufficient. Use Input & Output Channel 2.

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Temperature Calibration Lab - 4 - 3.1. Thermistor Measurements Connect the thermistor directly to the DMM and measure its resistance when placed in each of the five baths. Wait for the change in resistance readings to near steady-state. Discussion question : Can you estimate the time constant for the thermistor? Make a voltage divider circuit (diagrammed in Fig. 1) on a breadboard. Choose and measure an appropriate resistor R (nominally 220 W ) for the circuit. The excitation voltage E i = 1.5 V is provided by the DC power supply and the thermistor resistance represents the R TM in the figure. Add a connection of the circuit output to the oscilloscope to visualize the noise in the signal. Once you’ve identified noise in the signal, connect the circuit output to the filter stages. Figure 1: Voltage divider circuit. For each of the five temperature baths make the following measurements: Measure the temperature in the bath with the standard thermometer. Record the voltage indicated on the DMM. Now switch the BNC cable from the DMM to the A/D breakout box (NI BNC- 2090). Execute the LabView VI with an appropriate sampling frequency and sample length for each measurement, being sure to save the results. Draw an updated block and wiring diagram. SPOT CHECKS: For the 0ºC bath, does the experimental voltage you measured match what you would expect from a theoretical calculation of the voltage divider circuit (using your experimental value for the thermistor’s resistance)? Is the thermistor signal impacted by the wind tunnel operation? If possible, try to acquire a data set when the wind tunnel is off or at a low power setting. Does the voltage increase or decrease, as you expose the sensor to increasing temperatures? R R TM A/D and Multimeter _ + E i

Temperature Calibration Lab - 5 - 3.2. RTD Measurements Connect the RTD directly to the multimeter and measure its resistance when it is placed in each of the five baths. Note the settling time for the RTD to come to steady state, especially compared to the thermistor. Connect the RTD and power supply (1.5 V) outputs to the voltage divider circuit in place of the thermistor. The output from the circuit should connect to the BNC input 2 (on the lowpass filter side) of the filter unit. Connect the output of the amplifier to the A/D board and to the multimeter . Set the amplifier gain to 0 dB (no gain). Place the RTD in the 0° bath. Record the RTD voltage from the DMM and A/D board (separately, using the same settings as for the thermistor) and the temperature using the standard thermometer for all temperature baths. SPOT CHECK: Does the voltage increase or decrease, as you expose the sensor to increasing temperatures? Discussion question : What is the effect of the filter on these measurements?

Temperature Calibration Lab - 6 - Step-by-step Procedure Use Cart #4, making sure the filter unit is on the cart. 3.1 Thermistor measurements o Identify the thermistor and connect it to the DMM; o For each water bath (5 total): o Place thermistor in bath; monitor resistance measurement on DMM and note when value has reached steady state. Record resistance and time required to reach steady state for each bath measurement; o Make a voltage divider circuit and measure resistance of circuit resistor (220 W ); o Power circuit with V DC = 1.5V from power supply and connect thermistor output to voltage divider (as R TM ); o Connect circuit output to the oscilloscope and identify noise in the signal; o Connect circuit output to Input 2 of the Filter and output 2 of the Filter to the ADC breakout box and also the multimeter; o Select appropriate filtering settings on the amplifier based on the identified noise; o Open the LabView wiring block diagram for the acquisition VI file and locate the data acquisition tool. Find the DAQ board information (and FSI) and add to your Equipment List; o For each water bath (5 total): o Measure & record temperature of bath using the digital thermometer; o Record DMM voltage from voltage divider circuit; o Once the resistance is at steady state, run the LabView acquisition program. Save results; o Perform first Spot Check; o Draw block and wiring diagram. 3.2 RTD Measurements o Connect RTD output to DMM. o Measure steady state resistance for each water bath; record resistance and settling time; o Connect RTD output to voltage divider circuit; o Place RTD in 0°C bath;

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Temperature Calibration Lab - 7 - o Set preamp gain to 0 dB and connect voltage divider output to the Filter input; connect Filter output to the ADC box; o Turn Filter/Amplifier on; o Once the signal is at steady state, acquire the ADC voltage and thermometer temperature for each bath; o Power down Filter/Amplifier unit; o Draw new block and wiring diagram.

Temperature Calibration Lab - 8 - 4. Analysis, Results and Discussion Note: You should find the data sheets for the relevant instruments on your own, online. Make sure to reference your Equipment List for the necessary information. The LabView .lvm files can be opened in Excel if you edit the file extension from .lvm to .xls or .xlsx. 1. Thermistor: Using the data files you took in lab, calculate means and standard deviations for the voltages you took at each temperature, and plot mean voltage as a function of control temperature. Convert the voltage to a resistance. Plot the calculated thermistor resistance as a function of control temperature. Compare these calculations with the resistance measurements you took with the multimeter. Can you fit the calibration data using a linear regression? Also plot 1/temperature as a function of ln(resistance), and note the functional form; does degrees centigrade or Kelvin make more sense? Is it possible to determine the value for b from your analysis? Discuss. No uncertainty analysis is necessary for the thermistor results. 2. RTD: Using the data files you took in lab, calculate means and standard deviations for the voltages you took at each temperature. Based on these values, plot mean voltage as a function of control temperature. Fit the calibration data using a linear regression. Can you find a ? Apply a full uncertainty analysis to all results. 3. Comment on the significance and implications of the various spot checks and on the significance and implications of the various results graphs (including comments on sensitivity). Also comment on the advantages and disadvantages of using the different types of input circuits with the different types of measurement devices. 5. Analysis Guidance: Think about these questions while you’re performing the lab and planning the analysis. What is the title of this lab and what is the ultimate goal of this lab exercise? a. Is your calibration analysis a calibration of the individual temperature device or of the entire measurement setup? What is the difference between these two distinctions (think applicability of the calibration information) and what related aspects should you consider for the uncertainty analysis? b. What information do you need for the instruments, regarding their uncertainty sources and associated values? 6. Further Reading Figliola, Richard S., Donald E. Beasley, Theory and Design for Mechanical Measurements, 4 th ed. New York: Wiley, 2000. Chapter 7&8 Moore, John N, C. C. Davis, and M.A. Coplan, Building Scientific Apparatus, 2 nd ed. Reading MA: Addison-Wesley Publishing Company, 1989. Chapter 7. 7. Authors Written by M.S. Isaacson & C. Orison. Most recent revision: C. Farny (01/24).