We will compare using percent error actual value

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Unformatted text preview: e heart rate is (60s/min)/0.81s = 74 beats/min. This is a fairly typical resting heart rate, based on the values in Table 1. We can also calculate the interval times and compare those to the typical values in Table 1. We will compare using percent error: |actual value − theoretical value| × 100% theortical value Since the P − R interval gives a range, use the average, 0.16 s, as the theoretical value. percent error = 5 (5) Time difference (s) Peak Time (s) Peak 1 0.50 Peak 2 1.25 0.75 Peak 3 2.07 0.82 Peak 4 2.92 0.85 Peak 5 Table 2: Time difference between R peaks in Fig. 3. Interval length (s) percent error P−R 1.20 − 1.07 = 0.13 19% QRS 1.38 − 1.20 = 0.18 80% Q−T 1.52 − 1.20 = 0.32 16% Table 3: Comparison of interval values in Fig. 3 to the typical values in Table 1. 2.6 EMG An electromyogram (EMG) measures the electrical activity of muscles. As with the heart, other muscles in the body are also activated by ion flow across the cell membranes. In a clinical setting, this can be done to test for damage to the muscle or muscle-nerve connections, or to find the cause of a muscle weakness, paralysis, or twitching. As with the EKG test, electrodes are placed on the patient’s skin. The amplitude of the electrical activity correlates to the strength of the muscle contraction. It is also dependent on the quantity of nerve impulses that are sent to the muscle. For this reason, it is easy to observe large muscles like the biceps in the arm or the quadriceps in the leg. Smaller, less visible muscles can also be measured with an EMG. We will measure the electrical activity in the masseter muscle in the jaw. 3 Equipment The EKG sensor we will use today is very similar compared to those found in a medical setting, but somewhat simplified with the reduced number of leads. Since the EKG sensor looks at the potential difference between the various electrodes, we will start the lab with a brief experiment looking at known potentials using a simple voltmeter. The equipment we will use today includes: • Extech DC power supply • Meterman 15XP digital multimeter 6 • Pasco Scientific PK-9025 conductive paper with point electrodes • Vernier EKG Sensor • Vernier Go!Link • Vernier’s Logger Lite 1.6.1 software • alcohol wipes • adhesive electrodes 3.1 Extech DC power supply The power supply produces a fixed potential difference between two points. The power supply has two terminals, each of which should be attached to an electrode. Once they are attached, turn on both the power strip and the power supply itself, and set the "Output Voltage" to 10 V. 3.2 Meterman 15XP digital multimeter, functioning as a voltmeter A voltmeter is a device that can measure the potential difference (in volts) between one point and another. In this course you will frequently use a digital multimeter, which can function as a voltmeter, an ohmmeter or an ammeter. In order to set up the multimeter for use as a voltmeter, you should first turn the knob on the multimeter to V, so that the meter reads DC volts. Next, plug one lead into the ground or "COM" terminal and one into the terminal marked "V". (The third terminal, labeled "A mA µ A", is used for measuring currents.) If you hear your meter beep and turn off, that is a power saving feature. You can simply turn it back on by moving the selector switch over one setting and moving it back. Be sure to turn the meter off...
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