Let's Take A Vote...

Now you're debating terminology. Around our shop, if a thing is unboundedly large, we say "infinite." That does no harm. If you don't like that terminology, don't use it.

But it has no upper bound. What do you call that?

What do you call 1/x as x approaches zero?

None of that really matters. What matters is that using a latching relay can extend battery life by thousands, maybe millions. Not to mention whack thermal offsets down into the nanovolts.

John

Just thousands or millions.

Hours/hours, or picoseconds/picoseconds, are simple dimensionless numbers. "Thousands" is dimensionless so doesn't need any more words. Some people would add the word "of times" or ":1" which are also dimensionless, so needn't be said.

If I had wanted to specify the improvement in engineering units, I would have done so. But in this context, such units wouldn't make sense.

You get so upset over basics like this.

John

For some reasonably bounded value of infinite.

Reminds me of the 2 + 2 = 5, for larger values of two :)

People accept engineering roundoffs because to go finer, closer is buried in the noise or song of the universe.

Grant.

The term "electromotive force" was in use for over a hundred years before SI units were defined; the term is antique, and incorrect, and hardly anybody uses it in modern electronics. "Back EMF" is still sometimes used.

We measure voltage in volts, force in newtons. Volts are not force.

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The term electromotive force is due to Alessandro Volta (1745?1827), who invented the battery, or voltaic pile. "Electromotive force" originally referred to the 'force' with which positive and negative charges could be separated (that is, moved, hence "electromotive"), and was also called "electromotive power" (although it is not a power in the modern sense). Maxwell's 1865 explanation of what are now called Maxwell's equations used the term "electromotive force" for what is now called the electric field strength.[10]. But, in his later textbook[11] he uses the term "electromotive force" both for "voltage-like" causes of current flow in an electric circuit, and (inconsistently) for contact potential difference (which is a form of electrostatic potential difference). Given that Maxwell's textbook was written before the discovery of the electron, it is understandable that Maxwell exhibits what (in terms of modern knowledge) is inconsistency in the use of the term "electromotive force".

The word "force" in "electromotive force" is a misnomer:[12]

"[Electromotive force] has turned out to be an unfortunate choice of words which is still with us 160 years later. In all of physics except electromagnetic induction, the term 'force' is reserved for mechanical action on ponderable matter and is measured in units called Newtons. In contrast electromotive force is measured in units of Volts and causes charge separation."

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John

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Wow, this latching relay argument is really old! Just give it up and agree to disagree. Talk about something useful.

George H.

I know JF restarted it.. it takes two to tango.

Hey, I start lots of technical threads.

Do thermals matter to you? Latching relays are fabulous. As analog switches, no semiconductor comes close. We recently measured the wiper capacitance on the little Fujitsu parts we like, for a photodiode switching application. About 0.6 pF. Combine that with 1500 volt capacity, teraohm off resistance, 100 milliohms on, DPDT, drive isolation...

John

By your own statement, you admit that the duty cycle IS NOT ZERO, and therefore there IS a bound. And "duty cycle" does not cut it; if so, one could take a very large (latching, if that "helps") relay and operate it *once* using its required 200KW of power, to control one microwatt of load - and "therefore" have an absurdly large "gain" based on the "duty cycle" of almost zero.

The amount of bandwidth we've been wasting recently on exactifussitudes like this makes arguing about angels dancing on the head of a pin seem positively practical.

Personally, I make an average of about six stupid mistakes before breakfast, so I'm used to it by now. Fields has a private meaning for the word 'force', and Larkin is using 'infinite' in a loose sense.

As the cop said to Jack Nicholson in the last scene of the movie, "Forget it, Jake--it's Chinatown."

Cheers

Phil Hobbs

John Larkin wrote: : Do thermals matter to you? Latching relays are fabulous. As analog : switches, no semiconductor comes close. We recently measured the wiper

Indeed they are! Some types even work OK at sub-K temperatures where you cannot afford dissipating any heat at all. Talk about thermals! I find it amazing that the latching mechanism - which I suppose utilizes permanent magnets - still works there. We'll probably use those in a Quantum Metrology Triangle experiment.

Regards Mikko

John Larkin wrote: : Do thermals matter to you? Latching relays are fabulous. As analog : switches, no semiconductor comes close. We recently measured the wiper

Interestingly, in the LHe temperature OptoMOS switches can be closed but not opened. Switch-off relies on the charge leaking away from the MOSFET gate, and this leak obviously freezes.

Regards, Mikko

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Bounded by the end of the universe, perhaps. That's close enough to infinite for me.

ge

It's part of the power(in) calculation. If you're using the relay in the example Dewar the duty cycle (power(in)) certainly is important.

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You certainly do! Thanks,

Thanks they do sound nice.

(I'm just tired of the snipping back and forth... I should have just kept my mouth shut and moved on.)

George H.

Maybe you're just not waiting long enough. A 2N7002 will keep itself on or off, gate floating, for days. A cryo temps, that might extend to a few million years. I'm impressed that they work at all.

Possibly they use a silicon resisor for the pulldown, and the resistance goes way, way up when it's cold. So it might turn off in a few weeks.

Optomos SSRs are great signal switches too. I recently blew up a bunch of Clare parts, to find their voltage:current destruct limits. The datasheets are horrible about that.

Hey, you could make your own cryo latching SSR with a PV coupler, a PIN diode, and a couple of mosfets, using capacitive storage as the memory mechanism. Drive it with LEDs, cold or fiber-coupled from room temp.

John

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Just try injecting technical riffs - braininstorming in public - into the hen-clucking OT personal rants. Not only does that steer us back on topic, it annoys the hell out of some people who really deserve being annoyed.

John

What's the bound of 1/x as x approaches zero? Name a number.

Or one kilowatt

- and

Thanks. Finally someone is beginning to see my point.

John

Yes, pathetic for something clearly intended as an I/O component. I got no answer from them either about it.

As working engineers, we use a lot of terms in a loose sense. Like charge, average, infinite, heat, "Gaussian", power factor, Q, impedance, noise, exponential, "final", linear, all sorts of stuff that's mathematically imprecise. Because it's good enough to make things work. Somebody accused me here of not being a good scientist: guilty!

John