10
Output
The amplifier output is buffered and DC-coupled.
Therefore, possible offset currents fed into the amplifier
output by the following equipment (for instance a PC
data acquisition board), do not cause a DC offset.
Minimum
Modulation and
Overload
Control
LEDs indicate minimum modulation and overload
condition.
The LED “>5%” lights up at an output voltage higher
than 0.7 V. The LED “OVL” lights up if the output
voltage exceeds 9 V.
The optimum gain range is selected, if the LED “>5%”
lights up and the LED “OVL” remains dark. If both
LEDs remain dark, the gain should be increased. If both
LEDs light up the gain should be reduced.
The overload detector monitors both the amplifier
output and the filter input (see Fig. 2). By that means
overload condition will also be indicated when high
signal components beyond the filter pass band occur.
)
)
)
)
An overload detector at the integrator input is not pro-
vided. In some cases high level components at higher
frequencies may overload the amplifier stage before the
integrator while at the integrator output no overload
condition can be detected. To avoid this, make sure to
check the signal level in the switch position „ACC“
(integrator off) before switching on the integrators.
When the LED indicates overload you can use the low
pass filter to attenuate high frequencies.
2.
5. Filters
Low Pass
To eliminate disturbing noise or to comply with the
Shannon theorem: “Signal frequency should be less than
half of the sampling frequency”, it can be advantageous,
to use a low pass filter. For higher accuracy in the time
domain it is recommended to set the low pass at
1
10
the
sampling frequency.
The instruments of M68 series have 6 internal low pass
filters. The scale at the positions of the filter switch
“LOW PASS” is shows the 3 dB limiting frequencies in
kHz. The following table shows the 3 dB and the 10 %
limiting frequencies of the low pass filters:
