PeakTech 4055 Handbuch Seite 24

4.2.5. Amplitude attenuator
* The generator is set to "Auto" when startup. Press the key of【Atten】. Then the generator selects the
attenuation proportion automatically according to the magnitude of the set amplitude. The attenuation
switches when the output amplitudes are 2Vpp, 0,2Vpp and 0,02Vpp. Now, higher amplitude resolution
and signal-to-noise can be obtained regardless of the magnitude of amplitude.
The distortion of waveform is smaller. But a little instant jumping will occur for output signal when
attenuation switching, which is not allowed in some cases. So the fixed attenuation way is set for the
generator. Pressing the key of 【Atten】, the attenuation value can be entered by the numeric keys. The
attenuation is 0dB, 20dB, 40dB and 60dB. The knob can also be used to adjust the attenuation. The
attenuation will change one gear for each step. If the fixed attenuation way is selected, the attenuation step
will not be changed when the amplitude of signal changes So that the output signal within the whole
amplitude range will be changed continually. But if the amplitude of signal is small in the attenuation of
0dB, the distortion of waveform will be larger and the signal-to-noise ratio is worse.
4.2.6. Output load
* The setting value of amplitude is calibrated when the output end is open. The real voltage of output load
is the setting value of amplitude multiplied by the assignment ratio of load impedance, including
inductance and condensance and output impedance. The output resistance is about 50Ω. When the load
resistance is big enough, the assignment ratio approaches to 1. The voltage loss of output resistance can
be neglected. The real voltage approaches to the setting value of amplitude. But when the load resistance
is smaller, the voltage loss of output resistance cannot be neglected. It should be paid more attention that
the real voltage does not accord with the setting value of amplitude.
* With 50 output resistance, a momentary short-circuit of the output port makes no damage to the
generator, but the users should try to avoid long time short-circuit under high voltage output as a danger
of making damage to the generator. The generator has function of opposite voltage protection,
with which the generator close output automatically, make an alarm with the output indicating
light off when carelessly connect a high voltage(less than 30V) to the output port. Open the
output by pressing 【Output】key only after the fault cleared.
4.2.7. Offset-setting
In some cases, certain DC component should be contained in the AC signal to be output so as to produce
DC offset.
Press【Offset】key, the light of which will be on and the present offset value will be displayed. Input offset
value with the numeric keys or adjusting knob for the output signal to generate this DC offset to the output.
The relationship between the maximum DC offset and amplitude value should be below formula, if the
setting of offset exceeds, the generator will modify it until it is within the limit of the maximum offset value.
【offset】≤10-Vpp÷2
It must be paid attention that the summation of the half of the output amplitude of signal and the absolute
offset value should be less than 10V to guarantee the peak value of signal less than ±10V. Otherwise, the
amplitude-limited distortion will be induced. Besides, when the attenuation of channel A is selected auto, the
output offset will attenuate with the attenuation of amplitude. For the Vpp of amplitude greater than 2V, the
real output offset is the set offset value. For the Vpp of amplitude greater than 0.2V but less than 2V,the real
output offset is tenth of the set offset value. For the Vpp of amplitude less than 0.2V, the real output offset is
one percent of the set offset value.
It will be more convenient using the numeric keys than the knob when adjusting DC offset for output signal.
In general case, whether DC offset is positive or negative, DC level will rise if turning right and fall if turning
left. Sign of positive and negative will change automatically when passing through zero point.
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