relays

You don't accept the concept of the time-averaged power gain of a device?

Strange.

John

Tell that to the people who make RF amps. They specify them all in terms of time-averaged power gain.

John

I guess it's true what they said in those meetings - most people would rather be right than happy. ;-)

Cheers! Rich

I have said nothing more radical than the concept that average power gain is equal to average power out divided by average power in, as measured over some specified interval. That is numerically dimensionless, and happens to be equal to energy out over energy in, measured over the same interval.

You got a problem with that? Several people apparently do.

John

Strive for accuracy? Using coulombs to measure power? Confusing numerators and denominators, more than once? Stating flatly that division can only make numbers smaller? Dismissing all this slop as "brain farts"?

John

I did when I sent you the beer.

John

It's just like the datasheet spec for a power amplifier or a MMIC or whatever. The power gain is specified for steady-state operation with (usually) some specified power input and output level, with some specified input and load impedances, 50 ohms in most RF cases. Sometimes people specify a pulsed power gain, rather than steady-state, with some notes about durations and duty cycles. In that case, both the peak and the average output power are meaningful. All simple math. The non-latching relay equivalent for steady-state power gain would seem to be rated contact VA over coil power. It's now much more power you can control as a consequence of buying a relay.

OK so far?

In an actual application, with real signals and duty cycles and loads, there's nothing wrong with specifying a power gain over some time interval, based on average input power and average output power; that's numerically equal to the value you get using the input and output energies. The "real application" power gain is simply a definition, applied to a situation. In many cases, it has real meaning. Unless a definition is dimensionally wrong, there's no point in arguing about it.

All this should be obvious to the point of triviality. I can't understand why so many people are getting tangled up here. The only substantive issue is whether a value that's arbitrarily large and unbounded may be referred to as "infinite." We use that word as shorthand for unboundedly large; if people object to that use, fine, don't use it that way. If people get numerators and denominators backwards, or screw up simple arithmetic, that's another issue.

I seem to be arguing abstract math definitions with people who can't do simple arithmetic, or get their engineering units right.

John

Just one example: in another post you said, (cut and paste from the post):

"But that water will come out forever, with no further effort exerted on the valve. The longer you wait, the more output power, without limit. The output power is the *integral* of the input power.

If the output power is assumed constant, as you make clear (in a subsequent post) you are doing, then no matter how long you wait, you *don't* get more output power.

Clearly, you should have said "The longer you wait, the more output *energy*".

You are chastising other people about wrong use of engineering units, yet you make that same mistake. And, in responding to somebody who pointed out that you had said "power" when you should have said "energy", you didn't admit that you had made a mistake. You just amplified your point using the correct term, never admitting that you had made a mistake, to wit (again, relevant cut and paste from your post):

"The output energy is the (assume constant) output power integrated over time."

You could have tacitly admitted that you had made a mistake by prefacing this last sentence with "I should have said...", but you didn't. There was no admission of an error on your part.

It is said "Larkin _never_ admits error.", and you reply, "Sure I do, but I have to be wrong first." You used the wrong engineering unit in this case; will you admit your error?

Who is Dr Polemic?

John

VA has the engineering units of watts, and the VA rating of a relay contact (which is what they put on datasheets) is numerically and dimensionally the same as the maximum load power that the contact can switch. Why are you assuming that the load is AC? If AC, why are you reducing the "datasheet" power gain by assuming an unmatched/reactive load? Because it allows you to cut and paste another equation?

If a relay contact is rated at 120 VA, guess how many watts it can switch?

I can't think of a simpler way to explain this one to you... you've got me there.

John

Except that Power is not the simplistic E/t, it's dE/dt

And your assignation of power gain to a latching relay is down-right farcical.

...Jim Thompson

Now I have to explain the meaning of "steady-state" to you? What is this, the remedial electricity class?

Ditto "averaged."

John

Well, OK, I really don't have a lot to say to people who can't find the "divide" key on their calculator. Or those other people who don't know if the thing on top is the numerator or the denominator. Enjoy your new membership in the Parade of Clowns.

John