HP 120A - Page 14

Sect. IA Page 5
GENERAL CATHODE RAY TUBE PHOSPHOR AND FILTER INFORMATION
Below is a table of the most common phosphors used
in oscillography. These phosphors have been found
to meet all normal needs, ^oscilloscopes are fur 
nished with any of these four types, except that the
P2 phosphor normally should be used only in the
^)150A, as it has the necessary higher accelerating
potential recommended for this type phosphor.
Suitable filters used in conjunction with the proper
phosphor will enhance the usefulness of the oscil 
loscope by allowing the operator to select either a
long or short persistence presentation.
APPLICATIONS
Pl High visual efficiency. Brilliant green trace at
low accelerating potentials. Most commonly
used where visual observation is the main use of the
instrument. Suitable for photographic recording *
of repetitive or transient phenomena if there is no
need for moving-film photography. Relatively resis 
tant to burn damage from a stationary sweep beam.
P2 Highly versatile dual purpose phosphor for use
with accelerating potentials over 4KV: (1) A short 
persistence blue-green flourescence. (2) A long
persistence yellow-green phosphorescence. A yellow
filter effectively attenuates the short persistence
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* NOTE - The PH phosphor is the most sensitive
for photographic purposes. If the exposure time
using a PH phosphor is arbitrarily caHed 1, the re 
lative exposure time for the phosphors are Pl = 4;
P2 = 5; P7 = 2; PH = 1. Use of a blue filter will
reduce the light available by approximately 30%, thus
none should be used if very high speed traces are to
be photographed.
blue flash. A blue filter ♦ * masks the long persis 
tence yellow phosphorescence. The blue component
has good photographic efficiency * and the persis 
tence is short enough to allow continuous motion
photography of almost all traces. The persistence
of the yellow component is long enough to allow tran 
sients and low frequency traces to be observed easily.
A green filter will give a presentation similar to a
Pl phosphor. This phosphor is somewhat sensitive
to burning. If screen burning is a consideration, the
Pl phosphor is prefered.
P7 Similar to the P2 except more efficient * than
the P2 with accelerating potentials below 5KV.
May be used with filters ** to get both long and short
persistence displays. This phosphor is more sensitive
to burning than the other phosphors.
PH A short-persistence blue trace having high photo 
graphic efficiency * especially suited to con 
tinuous motion recording as well as visual observa 
tion of moving phenomena. The Pll phosphor has a
shorter persistence than a P2 phosphor viewed through
a blue filter. This phosphor is also sensitive to
burning.
** NOTE - When using the P2 or P7 phosphors with
a blue filter, the image will be quite dim. Care
must be taken not to turn the intensity too high to
overcome this, as the screen may be easily damaged
The use of a viewing hood is highly recommended
when operating the oscilloscope with a blue filter .
The use of the hood at all times is good practice,
as the intensity may be set to a lower level which
will help protect the CRT phosphor from possible
damage.
INFORMATION ON CATHODE RAY PHOSPHORS
Designation
Color
Spectral Range
Between 10% Points
Spectral Peak
Persistence
Fluorescent Phosphorescent
Pl
Green Green
0
4900 - 5800 A
0
5250 A Medium
(20 millisec.)
P2
Blue-green
YeUow-green
4500 - 6400
5430 both
phosphors
One Short
One Long
P7
Blue-white
Yellow
3900 - 6500
2 components
5580, 4400
One Short
One Long
Pll
Blue
Blue
4000 - 5500
4600
Short
(2 millisec. )
a