Electronics: Magnetic Fields and Protection Devices

Questions and Answers

What effect does twisting lead wires together have in minimizing interference?

It reduces the inductive coupling area. (correct)

It increases the electric field interference.

It enhances signal strength.

It allows for more magnetic-field pickup.

What is the purpose of voltage-limiting devices in an electrocardiograph?

To minimize reactive components in the circuit.

To amplify weak bio-potentials.

To protect the machine from high-voltage transients. (correct)

To increase the input voltage to the machine.

Which component is commonly used as a voltage-limiting device?

Resistor

Capacitor

Inductor

Silicon zener diode (correct)

How does common-mode voltage affect biomedical circuits?

It introduces unwanted noise. Signup and view all the answers

Which circuit element is NOT typically used for voltage limiting?

Operational amplifier Signup and view all the answers

What is the primary function of a transient-voltage-suppression (TVS) diode?

To protect sensitive electronics from voltage spikes Signup and view all the answers

In a driven-right-leg (DRL) system, how is common-mode voltage derived?

From a pair of averaging resistors connected to specific voltages Signup and view all the answers

What type of interference can a driven-right-leg (DRL) circuit help minimize?

Common-mode interference Signup and view all the answers

Which component is NOT typically considered a reactive component in circuits?

Resistor Signup and view all the answers

What is one method used to protect sensitive biomedical devices from electrical spikes?

Installing transient-voltage-suppression diodes Signup and view all the answers

Which interference source is most likely to affect bio-potential measurements?

Electromagnetic interference from RF signals Signup and view all the answers

What characteristic of electronic circuits can be attributed to reactive components?

Energy storage capabilities Signup and view all the answers

Which function does a resistor fulfill in a DRL circuit?

Creating a reference voltage Signup and view all the answers

What primarily causes artifacts in an ECG during cardiac defibrillation?

Voltage transients that saturate the amplifier Signup and view all the answers

What type of interference is represented in Figure 6.9 (a)?

Power-line interference at 60 Hz Signup and view all the answers

Which factor can lead to variability in electrode impedance affecting ECG readings?

Length of the connecting cable Signup and view all the answers

What method is typically recommended to reduce electric-field pickup in electrocardiographs?

Implement lead shielding Signup and view all the answers

What is a significant source of common-mode voltage in ECG measurements?

External electric fields from devices Signup and view all the answers

Which type of components are crucial for protecting circuits from voltage transients?

Reactive components Signup and view all the answers

Which issue is commonly caused by magnetic-field pickup in electrocardiography?

Irregularities in the ECG signal Signup and view all the answers

What can an amplifier experience due to unexpected voltage transients?

Saturation of its output Signup and view all the answers

Study Notes

Change in Magnetic Field and Current Induction

Change in magnetic field through a loop induces current in the circuit.
Minimization of induced current effects achieved by twisting lead wires together, keeping them close to body to reduce the subtended area.

Transient Protection in Electrocardiographs

Voltage-protection scheme at electrocardiograph inputs safeguards against high-voltage transients.
Voltage-limiting devices connected across limb leads protect the apparatus from voltage spikes.

Voltage-Limiting Devices

Various circuits for voltage-limiting include:
- Current-voltage characteristics of a basic voltage-limiting device.
- Parallel silicon-diode circuits.
- Back-to-back silicon zener-diode circuits.
- Gas-discharge tube (neon light) circuits.

Transient-Voltage-Suppression (TVS) Diode

TVS diodes protect sensitive electronic devices from voltage spikes along wires.
Acts as a safety mechanism for electronics in high-voltage situations.

Driven-Right-Leg (DRL) System

DRL system minimizes common-mode interference in ECG readings.
Utilizes averaging resistors to derive common-mode voltage, improving fidelity in readings.

Artifacts from Electric Transients

Defibrillation can induce voltage transients affecting ECG signals.
Transient effects can cause amplifier saturation, requiring a recovery period to restore proper function.

Problems with Electric Device Interference

Common interference includes 60 Hz power-line and electromyographic disturbances on ECG recordings.
For example, with a 9 m cable, detected interference current can be approximately 6 nA due to varying electrode impedance (up to 20 kΩ).
Shielding leads effectively minimizes electric-field pickup from surrounding electrical devices.

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Description

Explore the principles of current induction through changing magnetic fields and the various voltage-limiting devices used in electrocardiographs. This quiz covers transient protection methodologies and the function of transient-voltage-suppression diodes in safeguarding electronic devices from voltage spikes.