Honeywell Chadwick-Helmuth 8500C Maintenance Manual page 36

Chapter 4 - System Theory of Operation
f. Time-to-frequency Converter. The time-to-frequency converter converts the filtered
digitized signal to its frequency domain representation. The converter uses a block
floating point implementation of the decimation in time, radix two fast Fourier transform
(FFT) algorithm.
For spectrum analysis, a time domain Kaiser window is applied to 1024 samples, which
are then transformed into 1024 frequency domain points, of which 461 provide unique
unaliased information.
A high speed implementation of the Goertzel discrete Fourier transform (DFT) algorithm
is used to perform time-to-frequency domain conversion during balance data acquisition.
The firmware adjusts the number of samples used for input to the DFT according to the
specified measurement frequency.
g. Microprocessor. The 8500C microprocessor is an 8-MHz Motorola MC68008 with an 8-
bit external data bus capability. The 8500C+ uses a 25 MHz Motorla 68332 with a 16-bit
external data bus. The microprocessor performs the computations for the balancer/
analyzer System.
h. Memory. 8500C memory consists of 256 kilobytes (KB) of erasable, programmable, read-
only memory (EPROM), 128 KB of non-volatile random access memory (NVRAM), and
256 KB of dynamic random access memory (DRAM). The EPROM contains the system
operating firmware program, the NVRAM retains data in memory when power is
removed, and the DRAM is used for work space. 8500C+ memory consists of 1 MB of
non-volatile, random access memory (NVRAM), expandable to 2 MB. The EPROM is 1
MB of Flash memory and contains the system operating firmware program. The system
firmware is used for built-in self testing, display (LCD) management, user input
(keypanel) management, on-line context-sensitive help, print generation and printer
management, external storage (disk) management, internal storage (NVRAM and DRAM)
management, 8520C communications and control, single frequency vibration (balance)
measurement, and vibration spectrum analysis.
i. LCD. The LCD is the 8500C's primary means of providing a visual output to the user. The
LCD has a display resolution of 256 columns by 64 rows. Its pixel pitch is 0.53 by
0.53mm (8500C) or 0.52 by 0.52 (8500C+) (1:1 aspect ratio). The microprocessor
interfaces directly to the LCD via the system data bus. The LCD resides in the 8500C/C+
behind a tough plastic window which protects it from damage without degrading
readability. A resistive heater and EL lamp are integrated into the display.
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