Having less compute may mean even more cables: rather than having data sent over one cable then decoded, each line is either on or off, controlling: something.. (there could be signals here just contemplating). In modern stuff the logic is condensed, with data running between, in effect these older systems were one distributed logic unit. Probably over simplifying hut think of an old motorcycle, many cables, because you have to run power and ground back and forth all the way from switches to lights motors etc and back again.

[–] grue@lemmy.world 1 points 1 day ago (1 children)

Right, but even taking that into account, how many control signals could the thing possibly need?

If I enumerate every possible signal I can think of that a coal plant might need (boiler temp, fire temp, turbine speed, water flow, fuel hopper door control, etc.), and then arbitrarily multiply by an order of magnitude, my estimate is still lower than the number of wires I see in the pic.

[–] towerful@programming.dev 3 points 1 day ago

I'd take each of your metrics and multiply it by 10, and then multiply it by another 10 for everything you haven't thought about, then probably double it for redundancy.
Because "fire temp" is meaningless in isolation. You need to know the temperature is evenly distributed (so multiple temperature probes), you need to know the temperature inside and the temperature outside (so you know your furnace isn't literally melting), you need to know it's not building pressure, you need to know it's burning as cleanly as possible (gas inflow, gas outflow, clarity of gas in, clarity of gas out, temperature of gas in, temperature of gas out, status of various gas delivery systems (fans (motor current/voltage/rpm/temp), filters, louvres, valves, pressures, flow rates)), you need to know ash is being removed correctly (that ash grates, shakers, whatever are working correctly, that ash is cooling correctly, that it's being transported away etc).
The gas out will likely go through some heat recovery stages, so you need to know gas flow through those and water flow through those. Then it will likely be scrubbed of harmful chemicals, so you need to know pressures, flow rates etc for all that.
And every motor will have voltage/current/rpm/temperature measurements. Every valve will have a commanded position and actual position. Every pipe will have pressure and temperature sensors.

The multiple fire temperature probes would then be condensed into a pertinent value and a "good" or "fault" condition for the front panel display.
The multiple air inlet would be condensed into pertinent information and a good/fault condition.
Pipes of a process will have temperature/pressure good/fault conditions (maybe a low/good/over?)

And in the old days, before microprocessors and serial communications, it would have been a local-to-sensors control/indicator panel with every reading, then a feed back to the control room where it would be "summarised". So hundreds of signals from each local control/indicator panel.

Imagine if the control room commanded a certain condition, but it wasn't being achieved because a valve was stuck or because some local control over-rode it.
How would the control room operators know where to start? Just guess?
When you see a dangerous condition building, you do what is needed to get it under control and it doesn't happen because...
You need to know why.