Figure 3-24.Relay enclosures.
The clear plastic or glass covers provide a means of observing the operation of the relay without
removal of the cover. Figure 3-24 (D) and (F) are examples of a hermetically sealed relay. These relays
are protected from temperature or humidity changes as well as dust and other foreign material. Since the
covers cannot be removed, the relays are also considered to be tamper-proof. With metal or other opaque
covers, the operation of the relay can be "felt" by placing your finger on the cover and activating the
Q24. What is the operating principle of a relay?
Q25. How does a relay differ from a solenoid?
Q26. What are the two classifications of relays?