* Posts by Colintd

18 posts • joined 2 Dec 2016

Hooray, space boffins have finally got InSight lander's heat probe back into Martian ground again

Colintd

Re: First rule

"Precussive maintenance" is the technical term...

Airbus and Rolls-Royce hit eject on hybrid-electric airliner testbed after E-Fan X project fails to get off the ground

Colintd

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.

We regret to inform you there are severe delays on the token ring due to IT nerds blasting each other to bloody chunks

Colintd

The best things were the MAU relay testers. A large connector with a 9v battery, that when inserted into a port powered the related relay and opened the ring to the new device. You knew the relay had operated when there was a clunk, and you knew it had worked right when the network kept going (as the tester had loopback wires). Except we had one where the tester had been damaged inserting a new battery, and it didn't correctly loop. Use the tester, open the ring, wait for people to start shouting!

When is an electrical engineer not an engineer? When Arizona's state regulators decide to play word games

Colintd

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!"

Register Lecture: Can portable atomic clocks end UK dependence on GNSS?

Colintd

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.

Remember the Uber self-driving car that killed a woman crossing the street? The AI had no clue about jaywalkers

Colintd

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.

Never let something so flimsy as a locked door to the computer room stand in the way of an auditor on the warpath

Colintd

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...

Here's what Autonomy told its salesmen they were allowed to do

Colintd

What flavour is that?

A real head-scratcher: Tech support called in because emails 'aren't showing timestamps'

Colintd

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.

How'd your servers get that baby-smooth look? Dutch and Brit cool kids dunk Supermicro systems in synthetic oil

Colintd

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).

Crash, bang, wallop: What a power-down. But what hit the kill switch?

Colintd

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.

Colintd

Kill switches that go bang

Rather than silence I can speak from personal experience about what happens if you hit the kill/field dump switch on an NMR/MRI machine. All the stored energy in the coil vaporises the liquid helium coolant, followed.by a very loud bang/woosh as several thousand pounds of now gaseous helium, with about x1000 volume goes up the vent pipe. Had to be done as some idiot had come in with a steel gas cylinder which was literally dragged off the trolley into the coil. Not an experience to be repeated. Try leaning near the kill switch if you go for an MRI and see the techs.reaction...

Boffins build blazing battery bonfire

Colintd

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.

Haunted disk-drive? This story will give you the chills...

Colintd

Re: Sticky disc

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

Colintd

Sticky disc

In the early 90's we had a Compaq 33MHz 386 as a main build server, with a hard disc (can't remember the vendor or size) where they had made a bad choice of spindle lubricant. It would run indefinitely if left on, but if you turned it off overnight, the next day the disc wouldn't spin up when you turned it back on. The "trick" was to turn on the power, then lift up the whole case and give it a sharp twist. The inertia of the disc meant you overcame the static friction and the disc would then startup. Over time the twist required became larger/more sudden, but it lasted until we upgraded to a shiny new 486.

Phased out: IT architect plugs hole in clean-freak admin's wiring design

Colintd

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.

Google turns on free public NTP servers that SMEAR TIME

Colintd

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

Colintd

Re: We have also a Google time now?

The atmospheric drift leads to 10s of nanosecond level errors, which are way less than the impact of variable internet delays. That's what many stratum 1 NTP servers use GPS references, as do many mobile base stations.

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