Controlling the furnace

For steel the furnace needs at least 900 K. A gush of fuel and a spark get it there – but every combustion drives the pressure up as well. Whoever only heats soon sits in front of a furnace at 30,000 kPa. The control therefore needs two hands: one on the fuel, one on the exhaust.

The plant#

The simple furnace equalises with its pipes. So the chip controls the pipes:

• Pump “Brennstoff” pushes a combustible mixture into the input.
• Pump “Abgas” draws gas off the output.
• Activate on the furnace ignites.

Holding the temperature#

A hysteresis as with the room heater, only hotter: below 950 K it heats, from 1,100 K no more fuel comes in. In between the last state stays.

slt tmp temp T_OFF
and heat heat tmp
slt tmp temp T_ON
or heat heat tmp

It only ignites when fuel is coming and nothing is burning yet. Combustion tells whether it is already burning:

seqz spark burning
and spark spark tmp

Limiting the pressure#

The second hysteresis the other way round: from 5,000 kPa the exhaust pump runs, only below 4,000 kPa does it stop again. For steel from 1,000 kPa is enough, so the reserve towards the top is large.

Never against each other#

Fuel in and exhaust out at the same time would be a waste: the fresh fuel would go straight through the furnace into the exhaust. That is why the pressure locks the fuel:

seqz tmp vent
and tmp tmp heat

Only when the pressure is down again may it reheat. That costs a few seconds but saves fuel and keeps the two pumps from working against each other.

If the furnace is missing, all readings are NaN, both hystereses drop to 0, and both pumps stand still. A furnace the chip cannot see gets no fuel.