Posts by Colintd

Re: Frequency trimming?

The shifts in frequency are used to managed production capacity vs load.

When the network load is less than instantaneous generation capacity, the excess energy increases the kinetic energy stored in the turbines and they speed up, increasing the frequency. The governers then decrease the amount of steam being fed in, balancing the power, and lowering the speed/frequency to the target. When the network load is higher than the generation capacity, the turbines are robbed of kinetic energy, slowing down and decreasing the frequency. More steam in added, and the system comes back to balance.

Hence short term balancing is dependent on the inertia of the turbine/generator sets. The problem when a large fraction of the generation comes for inverter systems (batteries and solar), is that there is minimal inertia in the system, and it becomes significantly more unstable, and prone to trip outs.

Re: because MS-DOS was "heavily inspired" by 70s CP/M

Not quite. There was definitely a Windows NT 3.1. I have one of the first production copies, and was in Redmond as it was being released. 3.5 and 3.51 came later.

Re: Wobbley rampacks

Same here. A loaned ZX80, then my own ZX81 and finally a Spectrum, and 40years later I'm still working in tech!

Re: First rule

"Precussive maintenance" is the technical term...

Re: Electric planes?

Are you sure your data is correct?

https://en.wikipedia.org/wiki/Energy_density (and other references) suggests Jet 1A has a specific energy density of around 43MJ/Kg whereas Lithium ion batteries are between 0.4 and 0.9 MJ/Kg... That is between 50-100 times worse.

Even lithium-air is only 9MJ/Kg, so 5 times worse, and they are unproven technology.

In addition, as a number of others have noted, fuel is burnt so not present at landing. For batteries this is not the case.

Re: AKA Libertarians

Sorry but that's a feed for a classic joke;

"What's the difference between an electrical engineer and a civil engineer?"

"Electrical engineers build weapons systems, whilst civil engineers build targets!"

Re: end UK dependance on GPS?

I'm afraid you explanation is incorrect. A 3d fix needs 4 satellites as you need to solve for time and 3 spacial variables, which is why GPS receivers can typically provide very accurate time output, as they already solve for that.

The time/frequency references used for static telecoms start with a survey mode which removes 3 variables, and then allows you to get pretty accurate time with just one satellite (the ephemerides and an L2 receiver can give you a lot of ionospheric compensation).

Portable atomic clocks are great tech, but won't really help with GPS as even if you ignore relativistic drifts, you'd still need 3 sats for a 3d fix.

Re: Reasonable defaults

I suspect the default is static as otherwise the car would constantly undertake emergency brakeng when it fails to identify am object. This fits with the comment that the braking was disabled due to erratic behaviour. I'm not saying this is the right default, I'm just speculating about why it was set that way.

Re: Metal door

We had a mainframe room "upgraded" from high security key lock (which were good enough that I struggled to pick them) to an RF fob lock and one of those big magnetic latches. This was supposed to be for better security (with entry logs) for a high profile project. I demonstrated that I could open the new door either by flicking a mcb on the breaker panel (it was held shut with an active magnet, so fail open) or a really solid shoulder barge (once you opened up a small gap, the magnetic force drops off pretty sharply).

The new system was quickly replaced by some good high security physical locks...

What flavour is that?

Printing out email and dictating replies used to be 100% real in the time that you has physical circ folders for printed documents.

But then so did shared email accounts, where we did a daily download, via a modem, of email for our group, with was printed and circed, with batched sending of replies which had been prepared in text editors and transferred on crispy discs (crispies being the 3.5" followup to the 5.25" and 8" floppy)...

We also had "SneakerNet" for our first laserprinter, which meant you copied you file onto a disc, walked over to the machine with the printer attached, inserted the disc, and then did a local print.

Re: new spin on old tech?

I've got a dummy generator load which is an oil barrel with water and caustic soda inside. Neutral (earthed at Genny) to barrel, lengthy of live wire stipped and dangled in middle of barrel. Works a treat as long as you have good ventilation (to avoid explosion).

Re: A typically British response..

I remember that halon system going off in the taperoom for the Cambridge university mainframe during the late 80s. Minor fire went out, but the level of dust raised meant all the tapes had to go through a special wash/cleaning machine (actual liquid bath with sponge pads). Extremely disruptive.

Re: I'm not worried

You're mixing capex with opex. Just because it's much cheaper to build, doesn't mean it will be cheaper to run.

Re: Sticky disc

I'm sure you're right, and it was a Quantum drive. I'd forgotten all about them.

Re: Plot twist? What plot twist?

Having worked on these, the chassis was normally hot 100% of the time, because the oncoming mains went through a bridge rectifier with no isolating transformer. The chassis was connected to the -ve side of the rectifier, so you have a nice half-wave 240V potential on the chassis.

I was taught to work on these beasts with one hand in your pocket, as it minimized the chance of through body contact. More exciting was using a scope on these units, as connecting the shield (grounded) to the chassis (with 240V half wave) was a big no-no. The exciting approach was to let your scope float (plastic knobs only), the more sensible approach to use an isolating transformer for the TV, and then ground the chassis.

Re: We have also a Google time now?

As a 1st approximation, 1m of positional error is equivalent to 3ns time error (based on speed of light). So if you GPS location is good to 10m, the receiver knows UTC to better than +/- 30ns