Materials for Relay Arms

A relay arm (Figure 34.1) is both an elastic beam and a mini-busbar — that is, a current-carrying conductor in which the i²R losses must be kept small. The response time of the relay is limited by the lowest natural vibration frequency of the beam, and the dimensions of the beam are also constrained by the requirement that a given opening force, F, can deflect it by the (given) opening deflection, d — that is, its stiffness is prescribed. Furthermore, the beam must not fail by fatigue. We wish to achieve all this while minimizing its electrical resistance. The design requirements are listed in Table 34.1

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Figure 34.1 A relay arm. It must respond quickly, withstand fatigue loading, and conduct well.

Table 34.1 The design requirements