1. Field of the Invention
This invention relates to electric power distribution apparatus and more particularly to metering apparatus employing a radiation responsive data interface having a magnetically operated ambient radiation shield.
2. Description of the Prior Art
AC watt-hour meters having electronic registers with radiation responsive interfaces are known in the art. For example, U.S. Pat. No. 4,298,839 discloses apparatus including a four-channel optically coupled interface by which the electronic register can be selectively read and programmed by portable electronic programmer/reader apparatus which transmits an infra-red beam through the transparent cover of the meter. A radiation shielding baffle is provided between the infra-red emitters and detectors of the register and the transparent portion of the cover. The shielding baffle includes separate tunnel apertures each aligned with a separate pair of emitters and detectors to isolate the separate radiations for transmitting noninterfering radiation to and from the detectors and emitters. This arrangement provides satisfactory operation over a wide variety of operating environments.
Electronic registers often include light-emitting data display devices, such as vacuum-fluorescent numeric readouts. In installations were the light from such readout devices would be annoying or objectionable, or in certain situations to avoid attracting attention to the installation, means are provided to cause these light-emitting readout devices to become inactive during certain periods. Also included are means for temporarily reactivating the light-emitting readout devices upon command.
In some operating environments which exhibit a high level of ambient radiation, it has been found that undesirable responses by the optical interface may occur. It would therefore be desirable to provide metering apparatus having an electronic register which would provide protection against interference from high ambient radiation levels yet which would permit meter reading and programming operations to proceed without obstruction. It would further be desirable to provide such apparatus which would allow light-emitting readout devices of the meter to be energized upon command during those periods when such readout devices are normally disabled.