Power Conservation Schemes
Although the shelf life of vacuum relays is typically many years, occasionally a relay will show signs of "gassiness" after a relatively short period of non-use. A trace of gas released from its adsorbed state on the internal surface of the relay is usually responsible. Fortunately, this trace can normally be eliminated by the use of the high voltage processing procedure described below. The need for such processing can be readily determined by a simple, high voltage test just before installing the component in a system, which is good practice for any high voltage component. It is not necessary to high voltage process gas-filled relays.
High Voltage Process Procedure
- Connect a variable high voltage AC or DC power supply in series with a 10 megohm resister, a microammeter, and the relay (with the relay on the ground side of the power supply).
Immerse the relay in a dielectric fluid for processing. Transformer oil can be used but Flourinert (FC-77 made by 3M) is cleaner since it evaporates quickly from the relay surface.
Raise the voltage slowly. If the peak voltage is made equal to the maximum specified test voltage and less than 5 microamps of current is drawn at this level (or no glow is visible in a darkened room), then the vacuum is "hard" and no further processing is necessary.
If a glow occurs at a lower than maximum specified test voltage, hold the voltage just above the glow initiation level until the glow disappears; raise the voltage again to the onset of glow, or until the maximum specified test voltage is reached. If a DC supply is used, reverse the polarity and repeat the process.
Processing at levels up to 20% above the maximum specified test voltage may be done. Typical processing times range from one minute to several minutes for very high voltage relays.
WARNING: X-rays are produced during high voltage processing at voltages above 15 kV. See "Radiation Exposure at High Voltage: Is it A Problem?" for information on the precautions you should take when operating.
- SPST-NO relay: Process between open contacts.
- SPST-NC relay: Ground the base, energize the coil, and process between open contacts.
- SPDT relay: Connect the base and the NO terminal together, ground the base, and process between open contacts with the coil energized and de-energized.
- DPDT relay: Process each set of contacts in the same manner suggested for a SPDT relay.