What Is a Reed Relay?
A reed relay is a small relay containing a reed switch (a magnetic contact) controlled by a coil surrounding it.
What Is a Reed Switch?
Inside a glass tube, it's made of two thin ferromagnetic blades (reeds) that stick to each other with a magnetic field. When a magnet or coil approaches, the blades touch; when the field is removed, they open.
Turning Into a Relay
If a coil is wound around the reed switch, the magnetic field created when current is given to the coil closes the contact. So an isolated and very fast relay controlled by an electrical signal is obtained.
| Property | Value |
|---|---|
| Contact | Protected in a glass tube |
| Speed | Faster than a classic relay |
| Current | Low/medium (sensitive) |
Advantages
Since the contacts are sealed and gas-protected in a glass tube, they're clean, low-resistance and long-lived. It provides reliable switching on very fast and low-level signals.
Where Is It Used?
Automatic test equipment (ATE), measurement instruments, telecom, door/window alarm sensors (as a reed switch) and precise signal switching.
Contact Forms (Form A/B/C)
Reed contacts are classified as Form A (normally open), Form B (normally closed) and Form C (changeover, common terminal). The most common is Form A; it closes when a magnet/coil approaches. In alarm sensors Form C can be preferred to detect a break/tamper.
Common Mistakes
- Overcurrent: the thin contacts stick/melt at high power.
- Mechanical shock: the glass tube is fragile.
- Magnetic interference: strong fields nearby trigger it wrongly.
Frequently Asked Questions
What's the difference between a reed switch and a reed relay?+
Why is it preferred in test systems?+
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