3
Heating chamber
Mains voltage
See back of case
Dimensions of front
opening:
230 x 160 mm² approx.
Heating power:
800 W @230 V
400 W @115 V
Maximum temperature:
300°C @230 V
250°C @115 V
Temperature constancy:
±1°C approx.
Dimensions:
335x180x165 mm³ approx.
Weight:
5.6 kg approx.
4. Operation
The following equipment is also required to
complete the experiment:
1 Power supply unit for F/H experiment
@230 V 1012819
or
@115 V 1012818
1 Digital oscilloscope, 2x 30 MHz
1020910
1 HF Patch cord, 1 m
1002746
2 HF Patch cords, BNC/4 mm plug
1002748
Safety leads for experiments
1002843
Note: Before switching on, remove the
PE packaging part, which is located be-
hind the tube, from the inside of the heat-
ing oven.
Place front plate of the open side of the
heating chamber and fix it in place with 6
knurled screws.
Turn off the heating chamber and the con-
trol unit to begin with and turn all the knobs
on the control fully to the left.
Do not apply an accelerating voltage to
the tube when it is still cold (the mercury
inside may cause a short circuit).
Connect terminals "A", "F" and "K" (refer to fig.
2).
Connect terminal "E" of the Franck-Hertz
tube to the correct input on the control unit
by means of an BNC cable.
Connect the “FH Signal
U
Y
-
out” terminal of
the control unit to the Y input of the oscillo-
scope and terminal “
U
X
” to the X input.
Turn on the control unit and the equipment
should enter ramp mode.
Slowly set a filament voltage of 6 V. The in-
directly heated cathode requires about 90
seconds to warm up, once the voltage is ap-
plied.
Turn on the heating chamber. Set a temper-
ature of about 180° C and wait for the tube
to warm up (about 5 to 10 minutes).
Set the minimum acceleration voltage to
zero, slowly increase the maximum acceler-
ation voltage to 80 V.
Do not, however, increase the accelerating
voltage so much that self-discharge no
longer occurs inside the tube. Any ionisation
due to collisions will disrupt the curve.
Set up the oscilloscope initially with settings
of x = 1 V/div and y = 1 V/div.
Observe the emergence of the maxima in
the Franck-Hertz trace on the oscilloscope
screen.
Set up all the parameters, accelerating volt-
age, cathode filament, bias voltage and am-
plitude so that a trace with nicely delineated
maxima and minima is obtained.
The procedure as described so far is a gen-
eral setting procedure. Unavoidable differ-
ences resulting from the manufacture of in-
dividual Frank-Hertz tubes mean that the op-
timum parameters may differ from tube to
tube. The test report included with the tube
should give some idea of where good re-
sults may be obtained for the tube in ques-
tion.
The collector current displays regularly recurring,
equidistant maxima and minima that are inde-
pendent of the accelerating voltage. The interval
between these peaks is 4.9 V. A contact potential
of 2 V exists between the anode and cathode of
the tube, which is why the first maximum only ap-
pears in the region of 7 V. The first maxima will
be more obvious when the temperature of the
heating chamber is lower.
Evaluation of the Franck-Hertz curve:
To fully evaluate the Franck-Hertz curve, a dig-
ital voltmeter is needed. This does not require
that the current of the electron beam be deter-
mined precisely. The oscilloscope screen
should show the trace of a Franck-Hertz curve
featuring very clear maxima and minima.
Evaluation of the Franck-Hertz curve:
To fully evaluate the Franck-Hertz curve, a dig-
ital voltmeter is needed. This does not require
that the current of the electron beam be deter-
mined precisely. The oscilloscope screen
should show the trace of a Franck-Hertz curve
featuring very clear maxima and minima.
Connect a digital voltmeter between the sig-
nal output (
U
X
) and the ground socket (refer
to fig. 3).
