Today it is modern to have installed dual-rate electricity meter,
remotely controlled by load management, also known as demand side management (DSM).
The remote controlling is usually done using the ripple control method.
The advantage of the load management is that high power heating appliances and loads such as electric heater,
water heating, storage heater and so on are automatically switched on only
when applying a low tariff. The problem is that one does not know whether
low or high tariff is just applying and thus can not know when to manually switch on
other appliances. It is very advisable to switch powerful appliances (eg washing machine, air conditioning)
at the low tariff.
This led to the design of a simple device which indicates when the low tariff is applied. The apparatus consists of a transmitter and receiver. The transmitter is installed in a cabinet with circuit breakers. It is three-point connected: To the neutral, to the load management contactor and to the circuit breaker of outlet circuit. 22kHz signal from the transmitter is detected by the receiver, which indicates a low tariff by shining LED. The receiver can be plugged into any outlet in the apartment. (fed through a circuit breaker, to which the transmitter is connected - a signal spreads through the wall outlet circuit). The receiver inducctor has 85 turns of 0.2mm diameter wire on a ferrite rod with 2mm diameter and 20mm length.