If the vacuum tube heater in an approved...

🔍 Key Concepts

• Auto-alarm system fail-safe design – what should happen to the bell relay if a critical component fails? • Normally open vs normally closed contacts – how closing or opening a contact affects a relay coil • Purpose of the vacuum tube heater – what happens to current flow in the circuit when it burns out?

💭 Think About

• In a safety-critical alarm system, should a failure make the alarm more likely to sound, or less likely? Think about the intended "fail-safe" behavior. • If the heater burns out, does current stop or continue through that part of the circuit, and how would that affect relay energization? • Does closing contacts usually allow current to flow to a relay coil, or interrupt it? How does that compare with opening contacts?

✅ Before You Answer

• Decide whether a burned-out heater should energize or de-energize the bell relay in a fail-safe design. • Determine whether the vacuum tube heater failure should cause a contact pair to close or to open in order to achieve that behavior. • Match your conclusion about contact position (open/close) and relay state (energize/de-energize) with the choice that best fits.

If the vacuum tube heater in an approved auto-alarm system burns out:

A pair of contacts close and energize the bell relay

A pair on contacts open and energize the ball relay

A pair of contacts close and de-energize the bell relay

A pair of contacts open and deenergize the bell relay

🔍 Key Concepts

💭 Think About

✅ Before You Answer