Displaying A Diode Characteristic; Displaying A Hysteresis Loop - Philips GM 5605 Manual

Applications 21
C. DISPLAYING A DIODE CHARACTERISTIC
In displaying a diode characteristic the current through the diode is
plotted as a function of the voltage across the diode. For this, use can be
made of the circuit shown in Fig. 10. Voltage source E supplies a low
sinewave voltage. The resistance R must be small with respect to the
expected internal resistance of the diode. The voltage across R, which is
directly proportional to the anode current, is fed to the Y amplifier. The
anode voltage is applied to the X amplifier. Now a curve is displayed
which represents the relationship between anode current and anode
voltage.
Fig. 10. Displaying the diode characteristic of the OA 85
D. DISPLAYING A HYSTERESIS LOOP
In displaying hysteresis loops of magnetic material, the magnetic induction
B is plotted as a function of the field strength H. If the iron core of a coil
contains no air gaps, the field strength is proportional to the current
through the number of windings. The primary current is thus a measure
of the field strength H. A resistor Rp is connected in series with the pri-
mary winding. The voltage across this resistor is applied to the X input
(see Fig. 12).
The voltage across the secondary winding is Us = k.dB/dt.
Here k is a constant.
This voltage is integrated by an RC network (R» I/o>c). The voltage
across the capacitor then becomes Uc = k.B/R.C. The induction B is thus
proportional to the voltage across the capacitor. This voltage, which is
low and must be adequately amplified, is fed to the Y amplifier.