INFICON Composer Gas Concentration Controller - Manual (Page 57)

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Composer Operating Manual
2.6.2 Controller
IPN 761-600
The following sections describe the 761-600 controller; see the block diagram
in
Figure 2-7 on page 2-19 .
2.6.2.1 CPU (Central Processing Unit)
U30, U26, U28
The CPU section uses an Intel 80C196KC(U30) for the controller running at
19.6608 MHz along with a DS1244Y(U26) 32X8 battery backed RAM and a
PSD302(U28) for ROM and address decoding. The 80C196KC acts as the
master controller and performs all the functions necessary for Composer
operation except for sensor excitation and signal response functions which are
left to the DSP.
2.6.2.2 DSP (Digital Signal Processor)
U31
An Analog Devices ADSP-2101 is utilized to perform digital signal processing
functions to excite and analyze the acoustical response of the sensor. Its core
task is to perform as a locked amplifier to the excitation frequency. The
excitation is generated by a sine function approximation of the output of a 16
bit phase accumulator that has a phase increment added to it at a 16.384 KHz
rate. This arrangement allows frequencies to be generated by the size of the
phase increment by the following formula:
[29]
The locked amplifier task also uses the output of the sine function and its cosine
along with the returned signal from the sensor, and also by digital multipliers,
low pass filters and math determines the phase and amplitude of the returned
signal. The results can then be used to determine the acoustic resonance of the
sensor.
The clock for the ADSP-2101 is generated by its internal oscillator using a
19.6608 MHz crystal. The DSP’s clock output is used to generate the clocks for
the rest of the system. The program code for the DSP is downloaded from the
CPU after a power up reset.
Phase Increment
F
16384
65536
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