Required Parts, Software and Equipment Parts EET 150 Introduction to EET Lab Activity 12 Temperature Sensor Amplifier Project Figure 1 Flasher Circuit Component /alue Quantity LM741 OP AMP Integrated Circuit or Equivalent 1 LM34 or LM35 Integrated Circuit Temperature Sensor 1 1N4733 5.1 Zener Diode 1 Resistor 10 kω, ¼ Watt, 5% Tolerance 2 Resistor 27 kω, ¼ Watt, 5% Tolerance 1 Resistor 33 kω, ¼ Watt, 5% Tolerance 1 Resistor 47 kω, ¼ Watt, 5% Tolerance 1 Resistor 56 kω, ¼ Watt, 5% Tolerance 1 Resistor 100 kω, ¼ Watt, 5% Tolerance 1 Resistor 270 kω, ¼ Watt, 5% Tolerance 1 Resistor 470 kω, ¼ Watt, 5% Tolerance 1 Potentiometer 10 kω, ¼ Watt Multiturn 1 Equipment Required On-Campus Students Adjustable Dc power supply Solderless Experimenters' Board Digital Multimeter Hookup wire (22 AWG) Wire cutter/stripper Optional On-Campus Students 3 Banana jack leads red/black Required On-Line Students 2, 9 batteries 2, 9 battery snap connectors Solderless Experimenters' Board Digital Multimeter Hookup wire (22 AWG) Wire cutter/stripper Fall 2017 1 sensor.docx
Optional On-Line Students Adjustable Dc power supply Power brick DC-DC converter +5 to ± 9 dc Software MS Word Fall 2017 2 sensor.docx
Objective Construct and test an amplifier circuit that will increase the output voltage of a temperature sensor. The circuit output should be within the range of 0-5 dc. Determine how changing external component values effects the output of the circuit. Select a resistor value that gives a circuit output near the middle of the desired range. Theoretical Background The Operational Amplifier (OP AMP) is a building block of electronics. Adding external components turns this device into amplifiers and frequency filters. Other circuits allow the OP AMP to perform mathematical operations on input voltages. This project uses a single OP AMP of the type LM741 to amplify the output of a LM34/35 temperature sensor. The LM34/35 IC temperature sensors produce voltages proportional to the temperature in degrees F/C. The proportionality constant is 0.010/degree (10 m/degree). In the next activity, on-campus students will connect the amplified signal to a computer data acquisition (DAQ) board installed on a lab computer. On-line students will connect the output to the Analog Discovery 2 (AD2) scope input and use the data logger in WaveForms 2015 to record measurements. In both cases, the input will be an analog signal that represents the measured temperature. The amplification factor of an OP AMP circuit depends of the circuit configuration. Figure 1 shows the circuit configuration for a non-inverting amplifier circuit. The resistors labeled R1 and R2 determine the amplification of this circuit. The Zener diode labeled D1, limits the amplifier output to 5.1 to protect the input of the DAQ board/data logger. The OP AMP requires bipolar power supplies. Previous videos show how to connect the lab dc power supply to create the desired power source. Two 9 volt batteries can also provide a convenient power source. Formula 1 and measurements of the circuit input and output voltages provide a means of determining the circuit amplification experimentally. Formula 1 A out in Where: A v = oltage amplification factor. out = Measured output to DAQ board AD2. in = Measured input from sensor. Fall 2017 3 sensor.docx
Procedure 1.) iew the video associated with this project. Construct the circuit shown in Figure 1 on a solderless experimenters board. Use the pinout diagram included in the IC data sheet to convert the schematic symbol locations to the IC pins. 2.) Connect the input to a 0.25 dc source for circuit testing. This source can be derived from 0-6 volt source on the triple output supplies in the lab or from another dc supply. The project video shows an alternative method that uses a Ohm potentiometer and the positive 9 supply to derive this voltage. R1 9 + R2 U1 LM741/NS Connect this point to acquisition board DAQIN in + 0.25-9 - out Test circuit with 0.25 dc from power supply. Remove supply and connect temperature sensor after testing. D1 1N4733 Figure 1. Sensor Amplifier Test Circuit. 3.) Use a multimeter to measure the input and output voltages and record them in Table 1. Maintain the input voltage constant at 0.25 dc while making all the measurements required in the table. 4.) Turn off all power supplies. Disconnect all batteries if using them for a power source. 5.) Remove the dc source or potentiometer from the circuit input and replace it with the temperature sensor you are given. The accompanying project video shows how to make the following connections in detail. Figure 2 shows the connections for the temperature sensor. Use the pinout included in the LM34/35 data sheet to make the correct power, ground and signal output connections for this device. Use the +9 supply from the OP AMP to power the sensor. Determine if the sensor is an LM34 or LM35 by examining the markings on the device. Record the type in Table 2. Fall 2017 4 sensor.docx
R1 R2 Install temperature sensor 9 LM34/35 9 + -9 U1 LM741/NS DAQIN acquisition board D1 1N4733 Figure 2. Sensor Circuit With Temperature Sensor Installed. 6.) Replace resistor R2 with a 100k value if you have an LM35 device. Change the value of R2 to 33k if you have the LM34 device. Turn on the power supply or reconnect the batteries for the OP AMP/sensor circuit. The output voltage should be 2.5-3.25 dc if the circuit is connected properly. 7.) Measure the circuit output and record it in Table 2. Use the measured value of A vm for the value of R2 then use Formula 2 to estimate the room temperature in degrees C or F. Record these values in Table 2. Formula 2 T A vm out 0.010 /degree Where: T = Measured temperature out = measured circuit output voltage A vm = measured circuit amplification factor 8.) On-Campus Students: Keep the power supply on. Obtain a soldering iron and connect it to the ac power. After the iron has heated to temperature, bring it near the temperature senor. DO NOT TOUCH THE SENSOR WITH THE HOT SOLDERING IRON. Observe the changes in the circuit output. Does the voltage increase with higher temperatures? Turn off all power supplies and disconnect the soldering iron after making your observations. On-line Students: Keep the power supply on. Obtain a hairdryer and connect it to ac power. Turn on the hairdryer and direct its air toward the temperature sensor and away from the OP AMP chip and other components. Excessive heat can cause component failure. Observe the changes in the circuit output. Does the voltage increase with higher temperatures? Remove the batteries from the circuit after making your observations. Fall 2017 5 sensor.docx
Temperature Sensor Project Measurements Table 1 - Amplification Measurements R2 alue (ohms) in (dc) o (dc) Theoretical A vt Measured A vm 2.00 27k 3.70 33k 4.30 47k 5.70 56k 6.60 100k 11.00 270k 28.00 470k 48.00 Table 2- Estimated Room Temperature alue Sensor type (LM34/LM35) Measured A vm Measured out Computed Temperature Fall 2017 6 sensor.docx