Microsoft LPF-00004 Manual del operador descargar pdf (Pagina 25)

FUNCTIONAL DESCRIPTION Page 7

CYBERAMP 380, COPYRIGHT MARCH 2002, AXON INSTRUMENTS, INC.

Gain.

The gain can be set at discrete values ranging from x1 to x20,000. If all amplification of

a signal occurred before the low-pass filter, it is likely that noisy signals would drive the filter

into saturation even though the signal itself might be within the linear range of the electronics.

If, on the other hand, all amplification occurred after the filter, the inherent noise of the filter

would be amplified. The CyberAmp 380 implements a flexible approach. Amplification occurs

before and after the low-pass filter in an optimized division of gain.

Pre-filter gains:

x1, x10, x100

Post-filter gains:

x1, x2, x5, x10, x20, x50, x100, x200

Notch filter.

A tuneable notch filter is located after the low-pass filter. The notch filter can be

tuned in the field to reject 50 Hz or 60 Hz line-frequency noise. The notch filter can be

switched in or out.

DC offset.

A 16-bit D/A converter is used to introduce an offset into the signal pathway. This

offset is summed with the signal after the pre-filter gain. Thus the offset range and resolution,

as referred to the input, depend on the pre-filter gain settings.

Pre-filter gain Offset range Offset resolution

x1 ±3 V 100 µV

x10 ±0.3 V 10.0 µV

x100 ±0.03 V 1.00 µV

Zeroing.

In some instances it is desirable to zero out the DC content of the signal. This can be

done automatically by the CyberAmp 380. When Autozeroing is requested the baseline of the

requested channel is sampled and the DC offset is adjusted to continuously subtract that value

from the signal.

Automatic offset calibration.

At the high gains available in the CyberAmp 380, the internal

offsets of the amplifier sections could lead to substantial output voltages. This is prevented by

automatic self-calibration. In brief, the offset calibration procedure is as follows. The inputs

are internally grounded, the output voltage is compared to zero and the D/A converter is

adjusted until the output voltage equals zero. The inputs are then reconnected and the

commanded DC offset, if any, is added to the offset calibration value of the D/A converter.

This procedure usually takes just a few milliseconds. During this time, the output is grounded.

Calibration is automatically initiated when channel settings are changed. Not all setting

changes require an offset calibration cycle. For example, changing the low-pass filter frequency

does not force an offset calibration, but changing the gain does. The host computer does not

have to request an offset calibration; it is performed automatically when required.

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