Download BME 3511 Bioelectronics I - Laboratory Exercise #1 Digital

BME 3511 Bioelectronics I - Laboratory Exercise #1
Digital Multimeters
Introduction:
Electrical measurements are essential techniques for trouble shooting electronic
equipment/circuits. The three quantities of voltage, current, and resistance are the basis for most
analyses of both constant (direct current DC) and time variant (alternating current AC) circuits.
Frequency, capacitive reactance, and inductive reactance are three additional factors related to
AC circuits.
Multimeters are the most frequently used instrument to measure current, voltage, and resistance.
Digital Multimeters (DMM) are convenient, accurate, portable, and durable. MCM DMM
Model 72-7940 is an inexpensive, yet relatively accurate DMM that will be used in BME 3511.
Note on Biomedical Electronics Lab Safety:
Electric shock can be fatal; read and heed the BME 3511 Bioelectronics Safety Guidelines.
In general, the undergraduate BME electronic laboratory experiments conducted in BME
Teaching Laboratories, do not use voltages greater than 30 V (± 15 V); therefore, the chance of
receiving an electrical shock is greatly reduced. However, all voltages do have the potential to
burn materials and start fires, destroy electronic components, and present hazards to the person
performing the operations. Common sense and an awareness of electrical circuits is important
whenever you are working on these experiments.
Objective:
Become familiar with DMM functions and characteristics; and with the techniques for using a
DMM to measure resistance.
Understand and apply the concepts of measurement accuracy and measurement precision.
Laboratory Equipment and Supplies:
DMM
Assorted Resistors
Page 1
Background:
The MCM DMM Model 72-7940 features a rotary switch that can used be to select various
functions and range of measurement values. See Digital Multimeter DMM Model 72-7940
Functions, Ranges, Resolutions, and Accuracy (page 4).
Refer to the DMM itself for examples of the function labels; starting at the top center and
moving clockwise: Off, AC Voltage, DC Current, Square Wave Output, Battery Tester, Diode
Test, Resistance, and DC Voltage. Note: There is no AC Current function.
The DMM features also include three display symbols:
Low Battery
- +
Negative Value
Value Exceeds Selected Range
The terms accuracy and precision are associated with scientific and engineering measurements.
Accuracy describes the difference between the measurement of a quantity and the true value of
that quantity.
Precision is the degree to which repeated measurements under unchanged conditions show the
same conditions.
A measurement system can be accurate but not precise, precise but not accurate, neither, or both.
For example, if an experiment contains a systematic error, then increasing the sample size
generally increases precision but does not improve accuracy. The result would be a consistent yet
inaccurate string of results from the flawed experiment. Eliminating the systematic error
improves accuracy but does not change precision. A measurement system is designated valid if it
is both accurate and precise. Related terms include bias (non-random or directed effects caused
by a factor or factors unrelated to the independent variable) and error (random variability).
The terminology is also applied to indirect measurements; that is, values obtained by a
computational procedure from observed data. In addition to accuracy and precision,
measurements may also have a measurement resolution, which is the smallest change in the
underlying physical quantity that produces a response in the measurement.
http://en.wikipedia.org/wiki/Sensitivity_(tests)
Page 2
Procedure: Measuring Resistance Values
1. Use the DMM, (see Measuring Resistance, page 5) to measure the values of a nominal
33 Ω, a 6800 Ω, and a 1.5 MΩ resistor. Use Table 1 of the Laboratory Exercise # 1 Report Form
to record values and interpretation of each of the display symbols for each of the five DMM
Resistance Measuring Ranges.
2. Use thee sets of three resistors of varying values: R1A, R1B, R1C, R2A, R2B, R2C, R3A, R3B, R3C;
use the resistor codes to identity the nominal values.
www.hobby-hour.com/electronics/resistorcalculator.php
www.dannyg.com/examples/res2/resistor.htm
Record the nominal values in Table 2 of the Laboratory Exercise # 1Report Form.
Measure the resistance five different times for each of the nine resistors and record the
measurements in Table 2. (You should have recorded a total of 45 resistance measurements.)
Transfer the measurement values to an Excel spreadsheet and calculate the mean (AVERAGE)
and standard deviation (STDEV) for each resistor, record the calculated values in Table 2.
Note: You may also use a pencil & paper, a calculator, or an other computer application program
such as MatLab, Mathematica, SPSS, JMP to perform the statistical calculations.
Safe guard your five resistors from Laboratory Exercise #1.
You will need these same resistors for later laboratory exercises.
You must annotate any references you consulted in answering the following questions.
You may wish to use a word processor to complete your answers and attach the printout to your
Laboratory Exercise #1 Report Form.
3. The MCM DMM Model 72-7940 is described as having a so called 1.9999 display. Explain
the meaning/interpretation of a 1.999 display.
4a. Use the target analogy to differentiate among accuracy, precision, bias, and validity.
4b. Use the flawed tape measure analogy to differentiate among accuracy, precision, bias,
and validity.
5a. How would the accuracy of your measurements be affected if the number of measurements
had been increased to 20 measurements for each resistor? Briefly explain your answer.
5b. How would the precision of your measurements be affected if the number of measurements
had been increased to 20 measurements for each resistor? Briefly explain your answer.
6a. Briefly describe factors that might affect the bias in your measurements
6b. Briefly describe the factors that might affect the error in your measurements.
6c. Briefly describe a method for increasing the precision of your measurements.
7. Describe a procedure for making low-resistance measurements.
8a In checking for a short circuit, what DMM ohmic range should you select;
what measurement value would you expect for a short circuit?
8b. In checking for an open circuit, what DMM ohmic range should you select;
what measurement value would you expect for an open circuit?
9. Based on the results of this resistance measuring exercise, how many measurements do you
suppose should be made in determining the resistive values of a prototype circuit?
Briefly explain your answer.
Page 3
Digital Multimeter DMM Model 72-7940 Functions, Ranges, Resolutions, and Accuracy
Measurement
Resistance
Range
Resolution
200 Ω
2K Ω
20K Ω
200K Ω
2M Ω
0.1 Ω
1Ω
10 Ω
100 Ω
1000 Ω
Accuracy
Notes
± (2.5% +5)
Input Resistance 1M Ω
DC Voltage
0.2 VDC
2.0 VDC
20 VDC
200 VDC
300 VDC
0.1 mV
1.0 mV
10 mV
100 mV
1V
2 mA
20 mA
200 mA
1 uA
10 uA
100 uA
± (2.5% +2)
DC Current
± (2.5% +10)
Input Resistance 500K Ω
Frequency 45 - 400 HZ
AC Voltage
200 VAC
300 VAC
AC Current
NA
Battery Test
Range
1.5 V
9.0 V
0.1 V
1.0 V
± (2.5% +15)
Internal Resistance Maximum Current
60 Ω
25 mA
1800 Ω
5 mA
Out-of-Range /
Negative Value Source: MCM DMM Model 72-7940 Operating Manual
Page 4
Measuring Resistance Using the MCM DMM Model 72-7940
Warning
To avoid damage to the meter or to the device under test, disconnect circuit power and discharge
all the high-voltage capacitors before measuring resistance.
Measurement Procedure
The resistance measurement positions are: 200Ω, 2000Ω, 20kΩ, 200kΩ and 2000kΩ.
To measure resistance, connect the meter as follows:
1. Set the rotary switch to an appropriate measurement position in Ω range. The rotary switch
should be placed in the desired position prior to connecting leads. This position should not be
changed while the leads are connected.
2. Connect the test leads across with the component being measured. The measured value shows
on the display.
3. When resistance measurement has been completed, disconnect the connection between the
testing leads and the circuit under test.
Notes
If the value of resistance to be measured is unknown, use the maximum measurement position
(2000kΩ) and reduce the range step by step until a satisfactory reading is obtained.
The test leads can add 0.1Ω to 0.2Ω of error to resistance measurement. To obtain precision
readings in low-resistance measurement, that is in the range of 200Ω, short-circuit the input
terminals beforehand and record the reading obtained (call this reading as X). X is the additional
resistance from the test leads. Then use the equation:
Measured Resistance Value (Y) - (X) = Precision Readings of Resistance.
For high-resistance measurement (> 1M Ω), it may require several seconds to obtain a stable
reading.
If Ω reading with shorted test leads is not ≤ 0.5 Ω, check for loose test leads, or incorrect
positioning of the function selection switch.
The LCD displays / indicating an open-circuit for the tested resistor or the resistor value is
higher than the maximum range of the meter.
Source: MCM DMM Model 72-7940 Operating Manual
Page 5
BME 3511 Bioelectronics I Laboratory Exercise #1 Report Form
Digital Multimeters
I affirm that I personally participated in the collection and analysis of the data for this laboratory
exercise and that I personally contributed to the completion of this laboratory report.
Student Name: ___________________________________________
Signature: ___________________________________________ Date: __________________
I affirm that I personally participated in the collection and analysis of the data for this laboratory
exercise and that I personally contributed to the completion of this laboratory report.
Student Name: ___________________________________________
Signature: ___________________________________________ Date: __________________
Grade: ___________________
Grader Comments:
BME 3511 Bioelectronics I Laboratory Exercise #1 Report Form
33 Ohm Nominal Value Resistor
DMM Resistive Range
Display Value
Interpreted Value
200
2000
20K
200k
2000k
6800 Ohm Nominal Value Resistor
DMM Resistive Range
200
2000
20K
200k
2000k
Display Value
Interpreted Value
1.5M Ohm Nominal Value Resistor
DMM Resistive Range
200
2000
20K
200k
2000k
Display Value
Interpreted Value
Table 1 Interpreting DMM Displayed Values
R 1A
R 1B
R 1C
R 2A
R 2B
R 2C
R 3A
Nominal Value (Ohms)
Tolerance (%)
Lower Bound (Ohms)
Upper Bound (Ohms)
Measurement
#1
#2
#3
#4
#5
Average
Standard Deviation
DMM Accuracy (Ohms)
Range of Values (Ohms)
Table 2 Recorded DMM Measured Resistances and Calculated Average Values
R 3B
R 3C