ESA Certified Alarm Technician Practice Exam

What type of switch encloses the working parts in a hermetically sealed tube to protect the contacts?

1. Magnetic Reed Switch

2. Pressure Switch

3. Limit Switch

4. Proximity Switch

The correct answer is: Magnetic Reed Switch

A magnetic reed switch is the correct choice because it consists of two ferromagnetic contacts sealed within a glass tube filled with an inert gas or vacuum. This hermetically sealed design protects the contacts from environmental factors such as dust, moisture, and corrosion, which could lead to failure or unreliable performance. When a magnetic field is applied, it causes the contacts to close or open, allowing the switch to complete or break the circuit without being exposed to external elements. The other types of switches listed typically do not use a hermetically sealed design. A pressure switch usually operates based on the pressure of a fluid or gas and often has exposed components to the environment. A limit switch is designed to detect the presence or position of an object and might also be exposed to external conditions. A proximity switch detects the presence of an object without physical contact, often relying on sensing technologies that may also be susceptible to external factors. These switches do not offer the same level of protection for their internal workings as a magnetic reed switch does through its sealed construction.