GDP-32
II
DESIGN
Section 16, Page 13 May 2002
POWERLINE NOTCH FILTER
The Powerline Notch Filter can be set to reject the fundamental, 3rd, 5th and 9th
harmonics, or any other combination of four harmonic power line frequencies desired.
For example in a country with 50 Hz power mains, the standard filters supplied will reject
50, 150, 250 and 450 Hz. The filters are configured so that you can activate 50 and 150
Hz filters only, or all four simultaneously. The filters may also be bypassed for time-
domain applications and for operation in quiet areas. Be aware that use of these filters
will cause phase and amplitude distortion around the frequencies of rejection. Such
distortion can be removed by calibration with the filters enabled.
GAIN STAGES
Three amplifier gain stages, G0, G1, and G2 provide the signal gain available on the card.
G1 and G2 use binary gain steps from 1 to 128 giving a total system gain of 16,384.
However, during program operation the gain stages are limited to the range of 1 to 64
each, for a total system gain of 4096. The G0 gain stage is switchable between gains of
1, 4, and 16, for a total maximum gain of 65,536.
ANTI-ALIAS FILTER
This digitally tunable low pass filter is used to attenuate signal frequencies above the
desired pass band. Two frequency groups are available and are selected as a LO or HI
group. The low group extends from 1 Hz to 255 Hz in 1 Hz increments while the high
group extends from 100 Hz to 25.5 kHz in 100 Hz increments. An alias filter bypass is
also included for diagnostic testing.
MULTIPLEXER
This stage selects one of four input possibilities and presents the selection to the ADC for
conversion. The selections are as follows:
1. Analog - The output of the signal amplifiers is provided to the ADC. This is the
normal condition.
2. Reference - The ADC reference analog voltage is provided to the ADC that
normally represents a full-scale count of 32767.
3. Ground - Analog ground is connected to the ADC and should result in a 0 count.
4. Battery - A voltage of 0.1 times the actual 12-volt battery voltage is presented to
the ADC so that the attenuator is not needed. The displayed voltage is
multiplied by 10 and thus represents the actual battery voltage.
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