Armfield Instruction Manual
50
DAC Programming
A 12-bit DAC (Digital to Analogue Converter) Chip is used to control the Gear Pump
and PSV on the PCT40.
The chip is model number LTC1456. A datasheet can be found on the Internet by
entering the part number into a search engine such as Google.
The required output must first be coded into binary. The output can be from 0 to
4095.
All three lines should be set low (0). The most significant bit (MSB) should then be
set on line 2, and then a clock pulse should be sent on line 1. This is repeated until
the least significant bit (LSB) has been sent and clocked.
A load pulse should then be sent on line 3.
However, on PCT40, two chips are used in series, and so 24 bits must be sent
before the load pulse. The first 12 bits will control the hot water pump, and the last 12
will control the solenoid valve.
Cleaning the Equipment
Build-up of scale on the inside of the process vessels can be minimised by drying the
vessels when they are to be left unused for some time. Scale that does develop
within the large process vessel may be cleaned by hand.
It will be necessary to clean the filter in the pressure regulator at regular intervals. If
the filter is visibly obstructed or the inlet flow rate appears reduced then the filter may
need cleaning. Remove the filter from the equipment and clean by flushing with clean
water flowing in the opposite direction to normal flow. The frequency of cleaning will
depend on the cleanliness of the water supply.
Any build up of scale in the pipe work or process vessels can be removed by passing
a mild descaler through the system then flushing thoroughly with clean water. Any
stubborn deposits in the large process vessel can be eliminated by manual cleaning.
Remaining deposits in the smaller vessel may need longer soaking in descaling
solution. Always follow the instructions provided with the descaler regarding suitable
dilution of the chemical.
The water in both of the process vessels should be drained after use or at least
changed at regular intervals to prevent the growth of algae that may present a hazard
to health.
Accessing the electrical circuits inside the plinth
Maintenance of the PCT40 does not require access to the electrical circuits or
components located inside the moulded plinth. However, in the event of an electrical
problem it may be necessary for a competent electrician to gain access to the inside
of the mouldings as follows:
Ensure that the equipment is disconnected from the electrical supply (not just
switched off).
Drain any liquids contained in the process vessels and reactors, and remove any
flexible tubing connected to the pumps, valves etc.
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