Tektronix CURVE-TRACER 576 Instruction Manual page 30

Operating Instructions-Type 576
40. Remove the diode from the diode adapter and re-
place it with an 8 volt Zener diode. Align the diode so that
its cathode is connected to the emitter terminal.
41. Set the LEFT-OFF-RIGHT switch to RIGHT and
turn the VARIABLE COLLECTOR SUPPLY control clock-
wise. Note that the display shows both the forward and
reverse characteristics of the Zener diode (see Fig. 2-1 0).
.-.--.--r-.--r~r-.--.-.~--·
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Forward Bias ,
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Reverse Bias
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Fig. 2-10. Display of Zener diode I vs. V characteristic with PO-
LARITY switch set to AC.
Display Offset and Magnifier
42. Set the Type 576 POLARITY switch to -(PNP).
Note the display of the reverse voltage characteristic of the
Zener diode.
Note the display of the reverse voltage characteristic of
the Zener diode.
43. Position the display to the center of the CRT grati-
cule with the vertical POSITION switch (see Fig. 2-11A).
44. Set the DISPLAY OFFSET Selector switch to
HORIZ X10. Press the ZERO button and, using the hori-
zontal FINE POSITION control, adjust the spot so that it is
on the center vertical line of the CRT graticule. This spot
position represents the zero offset position. Release the
ZERO button and set the DISPLAY OFFSET Selector
switch to HORIZ X1.
45. Turn the CENTERLINE VALUE switch from the 0
position counterclockwise, until the Zener breakdown por-
tion of the display is within ±0.5 divisions of the center
vertical line (see Fig. 2-11B). Note the number on the
CENTERLINE VALUE switch which appears in the blue
window below the word DIV. This number multiplied by
the PER HORIZ DIV readout value gives the approximate
value of the breakdown voltage of this Zener diode. For the
diode in the example shown in Fig. 2-11, the approximate
Zener breakdown voltage is 4 divisions times 2 V /division
=
8 volts.
46. Set the DISPLAY OFFSET Selector switch to
2-12
HORIZ X10. Note that PER HORIZ DIVreadoutvaluehas
changed to indicate the 10 times multiplication. By expand-
ing the scale, a measurement can be made of that part of
the characteristic which was not quite offset to the center
vertical line of the CRT graticule (see Fig. 2-11C). This
val11e when added to the approximate value (or subratcted
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Fig. 2-ll. Displays of measurement of Zener breakdown voltage
using the DISPLAY OFFSET Selector and CENTERLINE VALUE
switches, (A) DISPLAY OFFSET Selector switch set to HORIZ XI
and CENTERLINE VALUE switch set to 0; (B) CENTERLINE
VALUE switch set to 4; (C) DISPLAY OFFSET Selector switch set
to HORIZ XIO.
if the approximate value was greater than the actual value)
produces a more exact measurement of the breakdown volt-
age. In the example shown in Fig. 2-11,400 mV should be
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