A model of the electromechanical characteristics, electrostatic characteristics and coil eddy
current losses of a reed relay was developed. These characteristics were returned from reed
and coil dimensions. The model was intended as an aid to the design of reed relays for Radio
Frequency (RF) and high voltage applications.
An electromechanical model of a reed switch and coil was developed using a combination of
an axisymmetric finite element model and analytical methods. The characteristics returned
from this model were operate, release and differential amp turns, contact gap and contact
force. Inclusion of results for contact resistance against contact force yielded the contact
resistance characteristics.
Electrostatic force between reed contacts was calculated and a criteria for contact arcing in a
vacuum applied to allow prediction of breakdown voltage in an evacuated reed switch.
The above elements were incorporated in a "Reed Switch Design Program" in which
operating, contact resistance and breakdown voltage characteristics were calculated from
reed and coil dimensions. Results were found to be in agreement with measured values for
three reed switch types.
Eddy current losses in relay coils were investigated through experimental measurement of
losses occurring in coils mounted around a copper conductor carrying a high frequency
current. The losses occurring in the coil were found to present an effective resistance to the
current in the conductor. The influence of coil dimensions and the magnetic properties of the
conductor on losses were observed. An analytical model of eddy current losses was derived
from first principals results and were found concordant with those measured.
An "RF Reed Relay Design Program" embodying the eddy current loss model and preceding
work was created to demonstrate how relay performance (and efficiency) can be enhanced by
tuning reed and coil dimensions. An example of its successful application to product
development at Crydom Magnetics Ltd is presented.
Proposals for future work are included.Crydom Magnetics Limite