Reed Switch - Switches

Unidentified MFG - 159-157-RA1 - Relay, Reed. SPDT Mercury Hg-Wetted, Form C,

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159-157-RA1 Relay, Reed. Mercury Hg-Wetted, Form C.

The mercury-wetted contact relay represents one of the more sophisticated types of relays made today. The early pioneer work in mercury-wetted contact switching dates back to the 1950’s, as telephone laboratory scientists sought out the “perfect contact”.

Reed relays use an external electromagnet to control the reed switch. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them. Sealed in a glass tube, the contacts are protected from corrosion. Mercury-wetted relays are fast in operation and have relatively good load carrying capacity and long life. The mercury films are reestablished at each contact closure and contact erosion is eliminated. The mercury films are stretchable, there is no contact bounce and because it is a mercury contact, the contact resistance is very low and idea for low level switching applications.

A mercury-wetted reed relay is a form of reed relay that employs a mercury switch, in which the contacts are wetted with mercury. Mercury reduces the contact resistance and mitigates the associated voltage drop. For high-speed applications, the mercury eliminates contact bounce, and provides virtually instantaneous circuit closure. Mercury wetted relays are position-sensitive and must be mounted according to the manufacturer's specifications. Because of the toxicity and expense of liquid mercury, these relays have increasingly fallen into disuse.

The high speed of switching action of the mercury-wetted relay is a notable advantage. The mercury globules on each contact coalesce, and the current rise time through the contacts is generally considered to be a few picoseconds. However, in a practical circuit it may be limited by the inductance of the contacts and wiring. It was quite common, before restrictions on the use of mercury, to use a mercury-wetted relay in the laboratory as a convenient means of generating fast rise time pulses, however although the rise time may be picoseconds, the exact timing of the event is, like all other types of relay, subject to considerable jitter, possibly milliseconds, due to mechanical imperfections. The only major weakness of a mercury wetted contact relay is the necessity to mount the relay within 30° of a vertical position, due to its position sensitivity.

Type: Form C

Contacts: SPDT.

Switched Load Rating: 2 Amp, 500 Volts Max, 100 VA Maximum

Carry Load Rating: 5 Amp

Contact Resistance: 14 Milliohms Typical, 20 Milliohms Max.

Packaging: Under High Pressure in Glass Capsules.

Approximate Dimensions 5.8mm D x 38mm Long. (0.225" X 1.5")

Life Expectancy: 1 billion operations minimum at rated load.

Note: Mercury Hg-Wetted.

Danger - High Pressure Glass Capsule- Handle with Care - User assumes responsibility and competency to handle this item.

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