112
'
5.
THERMIONIC EMISSION
The Schottky equation (5—9) has been tested experimentally '
over a wide range and found to be satisfactory for clean metals
but not for thoriated or coated laments.
'
EXPERIMENT 5—1
A TEST OF RICHARDSON’S EQUATÏON
Procedure.
1. Connect the apparatus as in gure 5—1. The
tube may
be any of the multi—electrode glass-envelope tubes if the
grids and plate are connected together. An old fashioned type
216 reCtier tube has been found particularly suitable. Tempera—
ture measurements of its pure tungsten lament are comparatively
easy to make.
The plate voltage V may be supplied by batteries,
a B battery eliminator or the local direct current supply line. If
the latter is used be careful of ground connections.
2. The temperature of the lament may be measured With an
,
optical pyrometer. This consists of a calibrated lamp in the eye—
pieCe of a teleScope and is adjusted so that the standard lameht '
andthat of the two-electrode tube are in focus at the same’time.
The current through the standard is varied until the two intensities are the same, and its value recorded.
The calibration chart
_
gives the temperature in terms of this current.* Since it is true
__
that the lament is always cooler near the supports, the
tion is
made at the-center of the wire. This same point
must be used in determining an unknown temperature. For
measuring the“higher temperatures, a more accurate comparison
.
is possible“ if a green ora red. glass is used over the eyepiece of the
‘
_
_pyrometer,pr0vided, of
the calibration has been madCî{
under-these
For very high temperatures, “a rotating
_
S€Ctor may be u3ed in front of the pyrometer. A,, calibrat10n
.
chart,
in operation, does not depend appreŒablÿ
Ôh the—“speed“0f-the Shutter provided it exceeds some
â secondïtdœs depend on the relative areas of the Shutter and
0penëpace * If “the —g‘las‘s‘ Walls of the two-electrode tube
the temperatureof the
metals raised” to melting 5point‘in’ a vacuum”. The melting
Pûb1î8hedltablcsof.phYSical constants
'
5.
THERMIONIC EMISSION
The Schottky equation (5—9) has been tested experimentally '
over a wide range and found to be satisfactory for clean metals
but not for thoriated or coated laments.
'
EXPERIMENT 5—1
A TEST OF RICHARDSON’S EQUATÏON
Procedure.
1. Connect the apparatus as in gure 5—1. The
tube may
be any of the multi—electrode glass-envelope tubes if the
grids and plate are connected together. An old fashioned type
216 reCtier tube has been found particularly suitable. Tempera—
ture measurements of its pure tungsten lament are comparatively
easy to make.
The plate voltage V may be supplied by batteries,
a B battery eliminator or the local direct current supply line. If
the latter is used be careful of ground connections.
2. The temperature of the lament may be measured With an
,
optical pyrometer. This consists of a calibrated lamp in the eye—
pieCe of a teleScope and is adjusted so that the standard lameht '
andthat of the two-electrode tube are in focus at the same’time.
The current through the standard is varied until the two intensities are the same, and its value recorded.
The calibration chart
_
gives the temperature in terms of this current.* Since it is true
__
that the lament is always cooler near the supports, the
tion is
made at the-center of the wire. This same point
must be used in determining an unknown temperature. For
measuring the“higher temperatures, a more accurate comparison
.
is possible“ if a green ora red. glass is used over the eyepiece of the
‘
_
_pyrometer,pr0vided, of
the calibration has been madCî{
under-these
For very high temperatures, “a rotating
_
S€Ctor may be u3ed in front of the pyrometer. A,, calibrat10n
.
chart,
in operation, does not depend appreŒablÿ
Ôh the—“speed“0f-the Shutter provided it exceeds some
â secondïtdœs depend on the relative areas of the Shutter and
0penëpace * If “the —g‘las‘s‘ Walls of the two-electrode tube
the temperatureof the
metals raised” to melting 5point‘in’ a vacuum”. The melting
Pûb1î8hedltablcsof.phYSical constants