Theory of Operation
Vibrex 2000 and Vibrex 2000 Plus User Guide 119
For more information on the EPROM chip, including replacement
instructions, see Section 6.3.2 “EPROM Replacement” on page 126.
6.2.2 Display Subsystem
The Vibrex unit’s display is a 64-by-128 pixel, reflective LCD. These
numbers equate to 8 lines by 21 characters. The display interfaces with
the main PCB through a 20-pin connector.
A programmable potentiometer circuit on the main PCB controls the
screen display’s contrast. This circuit retains the last contrast setting, even
after powering down. Adjust the potentiometer, using two keys located on
the keyboard to the right of the display.
For more information on the display, see Section 3.2.1 “Display” on
page 19.
6.2.3 Analog Subsystem
The primary purpose of the analog subsystem is to route, condition, and
filter the velocity vibration and azimuth (photocell system or Model 3030
Magnetic Pickup) signals. This subsystem also performs some self-
calibration functions.
6.2.3.1 Velocity Signal
The Vibrex unit routes velocity vibration signals from one of two
channels by a multiplexer (also called a mux). The unit offsets these
signals to 2.5V, then passes them through a two-pole high-pass filter
having a corner at 4 Hz. The signals then pass through a six-pole, low-
pass antialiasing filter with a corner frequency at 380 Hz.
These conditioned signals then go to a 13-bit ADC. The 13 bits include
12 bits to signify the number plus one for the sign (+ or -). A timing
processor unit (TPU) in the microprocessor controls the sampling. A
hardware state machine that uses discrete logic coordinates the data
exchange between the microprocessor and the ADC.
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