Experiment43ThermistorthermometerdesignExperimentalObjectives(1)Mastertheprincipleofthermistorthermometerdesign(2)DesignandassembleathermistorthermometerExperimentalInstrumentsDC stabilized power supply (0~30V); DC micro-ampere range is 0~100μA; thermistorand component transfer box, six-position resistance box, single-turn sliding rheostat(470Q/2W)asvoltage dividingresistor;Multi-turn slidingrheostat Ri,R2(4~9kQ/2W)multi-turn sliding rheostat R3 (10~15kQ/2W); toggle switch Kr, nine-hole experimentalplug-inboard;short-connectedpiece,multimeters.ExperimentalPrincipleThe thermistor element is used as a temperature sensing element by therelationship between thethermistor andthe temperature.Changesinambienttemperature can cause changes in the thermistor resistance, while bridges can be usedto convertchanges in resistance to voltagechanges, as shown in Figure4-2.In the figure,Ri、R2、and R3 are adjustable resistors, Rt is the thermistor.When the four resistanesare properly selected, the bridge can be balanced, and no current flows through themicro-ampere meter, that is, the micro-ampere meter indicates zero value, that isR _ R , the relationship is established.R,R,Figure 4-2 Schematic diagram of digital oscilloscopeIf the ambient temperature changes, the current will pass through the micro-amperemeter(thepointerisdeflected),thenthebridgeisinanon-equilibrium state
Experiment 43 Thermistor thermometer design Experimental Objectives (1) Master the principle of thermistor thermometer design (2) Design and assemble a thermistor thermometer Experimental Instruments DC stabilized power supply (0~30V); DC micro-ampere range is 0~100μA; thermistor and component transfer box; six-position resistance box; single-turn sliding rheostat (470Ω/2W) as voltage dividing resistor; Multi-turn sliding rheostat R1, R2 (4~9kΩ/2W), multi-turn sliding rheostat R3 (10~15kΩ/2W); toggle switch K1; nine-hole experimental plug-in board; short-connected piece; multimeters. Experimental Principle The thermistor element is used as a temperature sensing element by the relationship between the thermistor and the temperature. Changes in ambient temperature can cause changes in the thermistor resistance, while bridges can be used to convert changes in resistance to voltage changes, as shown in Figure 4-2. In the figure, R1、R2、and R3 are adjustable resistors, Rt is the thermistor. When the four resistanes are properly selected, the bridge can be balanced, and no current flows through the micro-ampere meter, that is , the micro-ampere meter indicates zero value, that is Rt R R R 3 2 1 = ，the relationship is established. Figure 4-2 Schematic diagram of digital oscilloscope If the ambient temperature changes, the current will pass through the microampere meter (the pointer is deflected), then the bridge is in a non-equilibrium state
and the size is relatedto theresistancevalue change ofthe thermistor,so that the currentcan be used. Characterizing the temperature, the measurement of the non-electricaltemperature can be converted into the measurement of the current in the micro-amperemeter, which is the basic principle of the thermistor thermometer temperaturemeasurement.ExperimentalContent and Procedure1. Select the value of Ri= R2 between 4~9kQ and adjust Ri and R2 to the selected valuewith the multimeter (this data needs to be recorded).According to therated power of the components used in the experiment, the values ofRi and R2 are between 4-9k2, and the corresponding voltage value is between1.3 ~1.8V.Rg is the micro-ampere internal resistance, measured with a multimeter and you shouldrecord it.2. Connect as shown in Figure 43-1. Be sure to hold the root when inserting andremoving components. Do not use force from the top!Replace the Rt access circuit with a six-position resistor box. The switch needs to bepulledtotheoffposition,andthevoltagedividerresistorpointershouldpointtothelowest gear(ex, the a-gear,which minimizes thevoltage divided bythe voltagedividing circuit).It should also be noted that the microampere current should flow fromthe positive end and out from the negative end.After the circuit is connected, the circuit can be connected after the teacher has passedthe inspection.3. Adjustment. Adjust the resistance of the resistor box to Rti, and turn on the regulatedpower supply to 2V.Coarse adjustment: first adjust the voltage divider resistor to the middle gear (d gear),then adjust R3 to make the micro-ampere meter initially zero, fine-tuning: increase thevoltage divider resistor to the maximum (g gear), carefully adjust R3 to make micro-ampere accurately refers to zero, at which point R3 = Rti. Note: Do not move after R isadjusted.4. Ued adjustment. First adjust the voltage divider resistor to the lowest (a gear), andadjust the value ofthe resistor box to the same time, then slowly increase the resistanceof the voltage divider resistor clockwise until the micro-ampere expresses the full bias.At this time, the value of Ued is the value set in the first step.Note: Do not move the voltage divider resistor. Ued is measured with a multimeter andthevoltagevalueshouldberecorded.Therelationshipbetween UedandRiandR2isverifiedafterclass.5. Calibrate the thermometer. Adjust the resistance box so that its resistance is equal tothe resistance of the thermistor at 65°C, 60°C,...25°C, and record the reading ofthe micro-ampere pointer.6. Verify the thermistor thermometer. Disconnect switch Ki, remove the resistor box.connect the thermistor Rt. Use this homemade thermometer to measure the temperatureofyourpalm.Comparethetemperaturevaluemeasuredbythethermistorthermometer
and the size is related to the resistance value change of the thermistor, so that the current can be used. Characterizing the temperature, the measurement of the non-electrical temperature can be converted into the measurement of the current in the micro-ampere meter, which is the basic principle of the thermistor thermometer temperature measurement. Experimental Content and Procedure 1. Select the value of R1= R2 between 4~9kΩ and adjust R1 and R2 to the selected value with the multimeter (this data needs to be recorded). According to the rated power of the components used in the experiment, the values of R1 and R2 are between 4~9kΩ, and the corresponding voltage value is between 1.3 ~1.8V. Rg is the micro-ampere internal resistance, measured with a multimeter and you should record it. 2. Connect as shown in Figure 43-1. Be sure to hold the root when inserting and removing components. Do not use force from the top! Replace the Rt access circuit with a six-position resistor box. The switch needs to be pulled to the off position, and the voltage divider resistor pointer should point to the lowest gear (ex, the a-gear, which minimizes the voltage divided by the voltagedividing circuit). It should also be noted that the microampere current should flow from the positive end and out from the negative end. After the circuit is connected, the circuit can be connected after the teacher has passed the inspection. 3. Adjustment. Adjust the resistance of the resistor box to Rt1, and turn on the regulated power supply to 2V. Coarse adjustment: first adjust the voltage divider resistor to the middle gear (d gear), then adjust R3 to make the micro-ampere meter initially zero; fine-tuning: increase the voltage divider resistor to the maximum (g gear), carefully adjust R3 to make microampere accurately refers to zero, at which point R3 = Rt1. Note: Do not move after R3 is adjusted. 4. Ucd adjustment. First adjust the voltage divider resistor to the lowest (a gear), and adjust the value of the resistor box to the same time, then slowly increase the resistance of the voltage divider resistor clockwise until the micro-ampere expresses the full bias. At this time, the value of Ucd is the value set in the first step. Note: Do not move the voltage divider resistor. Ucd is measured with a multimeter and the voltage value should be recorded. The relationship between Ucd and R1 and R2 is verified after class. 5. Calibrate the thermometer. Adjust the resistance box so that its resistance is equal to the resistance of the thermistor at 65 ° C, 60 ° C, ., 25 ° C, and record the reading of the micro-ampere pointer. 6. Verify the thermistor thermometer. Disconnect switch K1, remove the resistor box, connect the thermistor Rt. Use this homemade thermometer to measure the temperature of your palm. Compare the temperature value measured by the thermistor thermometer
with the temperature value displayed by the alcohol thermometer.7. After the experiment is finished, first disconnect the power switch and thendisconnectthecable.ExperimentalDataRecordingandProcessingRecording and processing of experimental data (the following need to print by yourself,Submityourreportinclass)1.Record the raw data, the list records the relationship between the resistancethermometercurrentandtemperature:Rg-Ri=R2=Ue-I,(μA)t(C)20253035404550556065702.Drawa calibrationcurve.Fromthelist of datadrawa calibration curveI3.Hold the thermistor with your hand and observe the measured thermistorthermometer
with the temperature value displayed by the alcohol thermometer. 7. After the experiment is finished, first disconnect the power switch and then disconnect the cable. Experimental Data Recording and Processing Recording and processing of experimental data (the following need to print by yourself, Submit your report in class) 1. Record the raw data, the list records the relationship between the resistance thermometer current and temperature: Rg= R1=R2= Ucd= (μA) g I o t( C) 20 25 30 35 40 45 50 55 60 65 70 2. Draw a calibration curve. From the list of data, draw a calibration curve g I -t 。 3. Hold the thermistor with your hand and observe the measured thermistor thermometer
4. Bring the recorded measured Ued into the formula (43-7), calculate and then,compare withthe value you selected, calculate the error, and analyzethe source ofthe error.Questions(1) Can you measure the resistance with an unbalanced bridge? If yes, please explainthe measurement method.(2) Consider the principle of the experiment and the experimental circuit used carefully,If the voltage divider resistor R is connected to the circuit by the current limiting methodcan theDCpower supplybeused to complete the experiment?Pleasedrawa circuitdiagram and analyzethe pros and cons of doing so
4. Bring the recorded measured Ucd into the formula (43-7), calculate and then, compare with the value you selected, calculate the error, and analyze the source of the error. Questions (1) Can you measure the resistance with an unbalanced bridge? If yes, please explain the measurement method. (2) Consider the principle of the experiment and the experimental circuit used carefully, If the voltage divider resistor R is connected to the circuit by the current limiting method, can the DC power supply be used to complete the experiment? Please draw a circuit diagram and analyze the pros and cons of doing so