HAMEG HM3033
Owner's Manual

input signal using theINVERT CH.II button is not possible. Lissajous figures can be displayed in the X-Y mode for certain measuring tasks: � Comparing two signals of different frequency or bringing one frequency up to the frequency of the other signal. This also applies for whole number multiples or fractions of the one signal frequency. � Phase comparison between two signals of the same frequency.

Should both input voltages be missing or fail in the X-Y mode, a very bright light dot is displayed on the screen. This dot can burn into the phosphor at a too high brightness setting (INTENS. knob) which causes either a lasting loss of brightness, or in the extreme case, complete destruction of the phosphor at this point.

Phase difference measurement in DUAL mode
A larger phase difference between two input signals of the same frequency and shape can be measured very simply on the screen in Dual mode (DUAL button depressed). The time base should be triggered by the reference signal (phase position 0). The other signal can then have a leading or lagging phase angle. Alternate mode should be selected for frequencies �1 kHz; the Chop mode is more suitable for frequencies <1 kHz (less flickering). For greatest accuracy adjust not much more than one period and approximately the same height of both signals on the screen. The variable controls for amplitude and time base and the LEVEL knob can also be used for this adjustment without influence on the result. Both base lines are set onto the horizontal graticule center line with the Y-POS. knobs before the measurement. With sinusoidal signals, observe the zero (crossover point) transitions; the sine peaks are less accurate. If a sine signal is noticeably distorted by even harmonics, or if a

Phase comparison with Lissajous figures
The following diagrams show two sine signals of the same frequency and amplitude with different phase angles.

Calculation of the phase angle or the phase shift between the X and Y input voltages (after measuring the distances a and b on the screen) is quite simple with the following formula, and a pocket calculator with trigonometric functions. Apart from the reading accuracy, the signal height has no influence on the result.
sin � = a b cos � =

�

1� �

( b) a

2

� = arc sin a b

DC voltage is present, AC coupling is recommended for both channels. If it is a question of pulses of the same shape, read off at steep edges. Phase difference measurement in DUAL mode t = horizontal spacing of the zero transitions in div. T = horizontal spacing for one period in div.

The following must be noted here:
� Because of the periodic nature of the trigonometric functions, the calculation should be limited to angles �90°. However here is the advantage of the method. � Do not use a too high test frequency. The phase shift of the two oscilloscope amplifiers of the HM 303 in the X-Y mode can exceed an angle of 3° above 220 kHz. � It cannot be seen as a matter of course from the screen display if the test voltage leads or lags the reference voltage. A CR network before the test voltage input of the oscilloscope can help here. The 1 M� input resistance can equally serve as R here, so that only a suitable capacitor C needs to be connected in series. If the aperture width of the ellipse is increased (compared with C short-circuited), then the test voltage leads the reference voltage and vice versa. This applies only in the region up to 90° phase shift. Therefore C should be sufficiently large and produce only a relatively small just observable phase shift.
12

In the example illustrated, t = 3div. and T = 10div. The phase difference in degrees is calculated from
�° = t · 360° = 10 · 360° = 108° 3 T

3 arc �° = t · 2� = 10 · 2� = 1,885 rad � � T
Subject to change without notice