Microsoft LPF-00004 Betreibershandbuch PDF herunterladen (Seite 49)

PRINCIPLES OF OPERATION Page 31

YBER

380, COPYRIGHT MARCH 2002, AXON INSTRUMENTS, INC.

Figure 12. Part A shows an inappropriate use of the notch filter. The notch filter is tuned for 50 Hz. The input

to the notch filter is a 10 ms wide pulse. This pulse has a strong harmonic at 50 Hertz that is almost

eliminated by the notch filter. Thus the output is grossly distorted. B shows an appropriate use of the notch

filter. An ECG signal is corrupted by a large 60 Hz component that is completely eliminated by the notch filter.

The notch filter in the CyberAmp 380 can be tuned to any value in the range 45-70 Hz. The tuning

procedure is easy and is described in the section Tuning the Notch Filter. Once tuned for the power-

supply frequency of a particular country, the notch filter should not require subsequent adjustment.

Overload Detection

The amplified signal may exceed the ±10 V acceptable operating range inside the CyberAmp in two

places: (1) at the output of the pre-filter amplifier (equivalent to the input of the low-pass filter), and

(2) at the output of the post-filter amplifier. If there were no filtering, overloads would only need to

be detected at the output of the final gain stage. However, the filter can feasibly reduce the wideband

noise of a saturating signal to low levels that can subsequently be amplified without saturation.

Overload detection circuitry located in both of these places is activated whenever the signal exceeds

±11 V. The limit of ±11 V exceeds the ±10 V recommended operating range in order to provide some

tolerance. There is no significant problem introduced by providing this tolerance, because the internal

amplifiers operate linearly for signal levels up to about ±12 V.

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Microsoft LPF-00004 Betreibershandbuch Seite 49