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Copy of: Re: small tube filling pressures
---------- Forwarded Message ----------
From: arturo de carlo, 101550,350
TO: INTERNET:EclectiKat@aol.com, INTERNET:EclectiKat@aol.com
CC: (unknown), INTERNET:NEON-L@NETCOM.COM
DATE: 4/16/96 8:48 PM
RE: Copy of: Re: small tube filling pressures
Lopals,
Hereunder I produce the table of backfilling pressures I use with my students
for over a long period of time.
For sure i'am not telling you that this is the ultimate list, but maybe you all
can look it over and compare it with your tables.
tubediam mm tubelength in cm Hgas+Hg in mbar neon in mbar
10 25 - 40 27 33
41 - 60 20 25
61 - 120 16 20
> = 120 13 16
12 25 - 40 25 32
41 - 60 19
24
61 - 110 15 19
> = 110 12 15
14 25 - 40 24 30
41 - 60 18
23
61 - 110 14
18
> = 110 11
14
16 20 - 35 22
29
36 - 55 17
22
56 - 100 13
17
> = 100 10
13
18 20 - 35 21
28
36 - 55 16
21
56 - 90 12
16
> = 90 9
12
20 20 - 35 20
27
36 - 50 15
20
51 - 80 11
15
> = 80 8
11
22 15 - 30 19
26
31 - 50 14
19
51 - 70 10
14
> = 70 7
10
> = 24 15 - 30 19
26
31 - 40 14
19
41 - 55 10
14
> = 55 7
10
The factor of calculation from mbar to Torr is x 0.75, but we only use the mbar
and soon we will use tthe Pa(scal) here in Europe.
Herein is: 100 kPa = 1 bar = 10 E3 mbar
so: 1 bar = 10 E3 mbar = 750 Torr = 100,000 Pa = 10 E5 Pa
1 mbar = 100 Pa = 10 E2 Pa = 0,75 Torr so:
1 Torr = 1.33 mbar.
The backfilled rare gas plays an important part in lamp starting, as we shall
see, and for that reason it's often called starting gas. It's also indispensable
for the merc vapour discharge itself. When merc vapour pressure is at the
correct level, i.e. self-absorption is minimal, the mean free path length for
electrons is so great that excitation of merc atoms, which generates converted
by the fluorescent layer to a longer wavelength the visible light, hardly take
place at all. The mean free path length of a particle is extremelu reduced
through the addition of an (rare) auxiliary gas, while the energy losses from
the discharge owing to elastic collisions of free electrons with the auxiliary
gas atoms remain sufficiently low.
As auxiliary gas pressure increases, however, the elastic collisions do drow
energy from the discharge to an increasing degree. This means that an optimum
level can be found for luminous efficacy at a certain auxiliry gas pressure as
the table avbove is showing you.
The auxiliary gas is also important for lamp life . Given a certain lamp life
reaquirment, the auxiliary gas pressure necessary for achieving this may very
well be higher than the optimum pressure for starting and light production. The
nature of the gas also has its influence. Energy trasnfer losses without
radiation become lower in proportion as the atoms become havier. This would
point to xenon as the most suitable gas. But there are two reasons why xenon is
less suitable, firstly excitation of xenon will take place owing to its low
excitation levels. This excitation however will not contribute to the desired
radiation, and the enrgy involved must be given up for lost. Secondly, xenon is
too expensive to be used in large quantities. The same holds in principle,
though to a lesser degree, for krypton. A dose however of krypton in the filling
gas of 10 mm diameter lamps, with the intention of keeping the arc voltage about
the same as for 15 mm diameter lamps is one thing to experiment with.
So we will hear from some guys on the list soon what the results are
experimenting with other rare gases then neon and argon for backfilling as I
shiped today some bottles to the other side of the Atlantic Ocean.
Make some tables and show all of us your test results. Is that a deal?
Best from dirk a. boonstra