An instructor is demonstrating a Wheatstone bridge circuit t…
An instructor is demonstrating a Wheatstone bridge circuit to a biomedical instrumentation class. The bridge has four arms (with resistors R1 to R4) and is powered by a DC supply. When all four resistors are equal, the voltmeter reads zero. The instructor then replaces R1 with a strain gage bonded to a test beam and presses on the beam, causing the voltmeter to give a reading. How does replacing one fixed resistor with a strain gage in a Wheatstone bridge allow the circuit to detect small resistance changes? The bridge amplifies the supply voltage in proportion to the gauge resistance, giving a larger absolute output. The bridge stores charge until enough resistance change accumulates, then releases it as a pulse proportional to total displacement. Starting from a perfectly balanced (zero-output) condition, any tiny resistance change in the gage arm immediately creates an imbalance voltage Vab that is directly related to ΔR, allowing small displacements to be detected. The other three fixed resistors act as reference standards that calibrate the gauge reading automatically on each measurement.
Read DetailsWhich of the following is NOT one of the five components of…
Which of the following is NOT one of the five components of the input signal to a biopotential measurement system? The desired biopotential Undesired biopotentials Amplified output signal Power line interference (60 Hz and harmonics)
Read DetailsWhat if the high-pass filter in an EMG measuring device fail…
What if the high-pass filter in an EMG measuring device failed and stopped functioning, essentially becoming a wire? If this happens during an EMG recording session on the patient’s bicep and the patient frequently moves his arm, disturbing the electrode-skin contact, what would most likely appear in the output signal? Complete loss of the EMG signal Large, slow-varying baseline wander and DC offset that could saturate the subsequent amplifier stages Increased 60 Hz power line interference Loss of the high-frequency components of the EMG signal
Read DetailsA neonatal intensive care unit needs electrodes for continuo…
A neonatal intensive care unit needs electrodes for continuous ECG monitoring of premature infants over several days. The electrodes must conform to the curved surfaces of tiny limbs and torso, remain comfortable, not require removal for X-rays, but the unit has a limited budget. Compare carbon-filled silicone rubber electrodes versus thin-film Mylar electrodes with Ag/AgCl deposition for this application. Carbon-filled silicone is better because it has lower impedance than thin-film electrodes Carbon-filled silicone is better because it provides better conformability to curved infant surfaces Thin-film electrodes are better because they are X-ray transparent and don’t need removal, despite having higher impedance Both are equally suitable since they’re both flexible electrode types
Read DetailsAs an action potential propagates along a nerve axon, it cre…
As an action potential propagates along a nerve axon, it creates electric dipoles. What is the configuration of charges in these dipoles, and how do they relate to measurable surface potentials? The action potentials produced by excitable cells inside the body have no effect on surface measurements Equal distribution of charges that cancel out any measurable potentials Alternating positive and negative regions that only exist intracellularly Positive charges inside and negative charges outside at the active region; these dipoles generate current loops that create measurable potentials in the extracellular space
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