EET 150
Lab Activity 13 On-Line Students
Temperature Logging and Display
Analog Discovery 2
Required Parts, Software and Equipment
Parts
None for this activity
Equipment
Analog Discovery 2: Arbitrary Waveform Generator (AWG). Two channel oscilloscope
Multimeter
Optional
BNC adapter board for Analog Discovery 2 Digilent 410-263
available at: http://store.digilentinc.com/bnc-adapter-board-for-the-analog-discovery/
1 BNC to alligator lead test cable
Software
Waveforms 2015 for Analog Discovery 2
Available for download at : http://store.digilentinc.com/waveforms-2015-download-only/
MS Word
Objective
Display the output of the temperature sensor circuit on a computer. Produce a time plot of temperature change over time using the Analog Discovery 2 (AD2) data logging function. Scale voltages to display a plot in degrees using WaveForms 2015 data logging program and AD2 scope input.
Theoretical Background
The output of sensors usually connects to a digital system that makes decisions based on signal level and/or displays the measurement results over time. The display and storage of sensor measurements is called data logging. A data logging system consists of a sensor with its associated electronics, an analog to digital converter that changes continuous signals into numerical values that a computer can read, and a software display program that plots and stores the values. This laboratory activity uses the data logging function of the Analog Discovery 2 (AD2) to convert the amplified voltage of a temperature sensor to a series of temperature measurements. The scope inputs of the AD2 serve as logger inputs and can display voltage values. The logger software can also modify the voltage values with simple arithmetic formulas to display the measured temperature.
Figure 1 shows a block diagram of the desired system for this lab activity. The signal
Figure 1. Data Logging System Overview.
amplifier connects the AD2 using the flywire leads. Use the channel 1 scope input to capture the circuit output voltage. The scope channels take the continuous voltage values from the signal amplifier and convert them to a series of numbers. The rate at which this conversion takes place is called the sampling rate. Since temperature changes slowly, the sampling rate for this lab can be quite slow when compared to the measurement of electronic signals. Once these signals enter the computer through the AD2, they are modified and displayed using the data logging function of the WaveForms software. The data logging function give users the ability to display the input signals as dc or true rms ac. It also provides a tablet of mathematical functions that can produce a plot scaled into the actual measured units. This software can store the samples for a predefined period for use in other analysis programs.
Procedure
1.) View the demonstration videos on how to connect the AD2 and use WaveForms software to take data samples. These demos show you exactly how to set up the hardware and software for this activity.
2.) Connect the flywire leads to the OP AMP circuit as shown in Figure 2. The sensor circuit connects to scope channel 1. Connect the AD2 to a computer using the USB
Figure 2. AD 2 Interface Logger Connections.
cable. Start the WaveForms program and open the data logger function.
3.) Figure 3 shows the interface to the data logger function of the AD2. Remove
Figure 3. Analog Discovery 2 Data Logger Interface.
all channels except the dc value on scope channel 1. This interface displays a time plot of the measurements and the current sample value. Set the update to 200 mS and the history to five minutes. The range is adjustable and an offset value can set the lowest plot value to zero. View the videos associated with this lab for a complete tutorial on the use of the data logger function for this project.
The data logger displays the dc output from the sensor circuit. Use Formula 1 below to scale the voltage to display the result in degrees.
Formula 1
Where: T = Measured temperature
Vout = measured circuit output voltage
Avm = measured circuit amplification factor
The LM35 will read degrees Centigrade directly after processing the input voltage with Formula 1. To convert the signal to degrees Fahrenheit, use Formula 2 shown below. The LM34 will display degrees Fahrenheit when processed by Formula 1 so use Formula 3 to convert the temperature to degrees Centigrade.
Formula 2 F=1.8∙C+32
Formula 3 C=0.555∙(F-32)
Where: C = temperature in degrees Centigrade
F = temperature in degrees Fahrenheit
The amplifier gain in Formula 1 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. Figure 4 shows the scaled channel with the scaling formula inserted. This formula is for a LM35 sensor that scales its output to degrees Centigrade. It assumes gain Avm=11.
Figure 4. Data Logger Channel Equation For LM35 Sensor.
4.) Connect the AD2 to the sensor circuit and apply power to the sensor circuit using the battery supply. Run the data logger function of the WaveForms software and check the plot for an output using the scaled channel and CH1DC. If voltages and temperature values appear that are near the ambient temperature, turn off the CH1DC channel.
5.) Obtain a hair dryer and apply the hot air to the temperature sensor. Avoid blowing hot air on the OP AMP and the AD2 because excessive heat can damage these components or cause their characteristics to shift.
6.) Record the temperature measured in Table 1 at 1 minute intervals for 5 minutes.
7.) Power down the temperature sensor circuit and stop the WaveForms program.
Table 1- Temperature Measurements
Degrees F / Degrees CAmbient
Heat Applied
1 minute
2 minutes
3 minutes
4 minutes
5 minutes
Fall 2017 1 tlogging.docx