The P.I.O. line which receives the signal is an interrupt line, so that each
time the zero crossing point signal is received the processor enters an interrupt
service routine. In this routine the thyristor is fired after a delay calculated from the
programmed speed requirement and the feedback speed. Figure 6 shows the firing
circuit. Adequate suppression has to be included to prevent interference with other
domestic equipment.
FIG 6
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The 5 V. power supply for the circuit to the right of the isolation boundary must
be derived from the 240 V. supply. If the 5 V. Nascom supply was used, there
would be no isolation.
The program for controlling the operation of the system, which consists of
sequencing for filling, emptying, pumping out and the motor control subroutine, was
developed using the Zeap assembler. A flow chart for the system on which the
program was based, is shown on the next page.
* + . +
* + . +
* + . +
* + .