| 摘要 |
A microprocessor-based zero crossing circuit produces in response to an input command provided by closure of a switch (18) an output signal (13, 14) which is synchronised with the zero crossing points of an a.c. supply and includes a predetermined delay. By this means the output signal (13, 14) may be used to operate or control operation of, for example, a circuit breaker for the a.c. supply in order to minimise contact arcing. The circuit is useful in an electricity supply meter when the input command on input 12 is generated by a credit or prepayment mechanism which acts to cut-off an a.c. supply on expiry of credit. Following a cut-off command on input 12 the circuit produces the synchronised output signal (13, 14) appropriately delayed to take into account the operating time of the circuit breaker so that its contacts (20, 21) open as nearly coincident as possible with a zero crossing point of the supply. |
