The Beede Control Meter Relay - How it works:
A vane attached to the moving coil of a Beede meter movement interrupts a beam of infra-red as the indicating pointer moves upscale and passes the set pointer. This interruption changes the state of a phototransistor attached to the set pointer, and switches an electronic circuit that either energizes or de-energizes the output relay.
As long as the indicating pointer remains above the set pointer, the electronic circuit remains switched. As the indicating pointer falls below the set pointer, the electronic circuit automatically returns to its former state.
|The basic mechanical construction of a Beede Control Meter Relay is a standard D'Arsonval meter movement. With infra-red source and phototransistor module mounted directly on the set pointer as in the drawing below. The set pointer position is determined by the adjustment knob or knobs.
|There are no prisms, other optics inductive coils, etc. A change in phototransistor voltage changes the input signal to a solid state voltage comparator that energizes or de-energizes the output relay as demonstrated in the drawing on the right.
Optional latching of either relay or solid state output is provided by means of positive feedback within the electronic circuit.
The Beede Control Meter Relay has been designed to be inherently fail safe. The output relays are normally connected so the relays are energized in the "safe" condition. Below a high set point or above a low set pointer. In case of a power failure or malfunction, the relays will de-energize. When power is restored, the unit will automatically provide the correct relay position. If required, a Beede Control Meter Relay can be wired so the output relays are energized on the opposite side of the set points.