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1.4
COMPUTER / CONTROL SYSTEM
1.4.1
General Description
The Computer Control System is embedded in the humidity generator. The computer
controls all aspects of the humidity generation process (i.e. controlling temperatures,
pressures, etc.) as well as performing all human interface functions of keypad input and
information display. The computer also controls printer operation and interfaces with an
external computer (optional) for bi-directional RS-232C communications.
The Computer Control System is considered a "single-point automation" unit, controlling the
functions of the humidity generator to bring it to any operator input setpoint. The computer
will always control the system at the most current setpoint that has been input, whether from
keypad input, or from external computer input through the RS-232C port. The Computer
Control System knows nothing of past or future setpoints, requiring the use of an external
computer if automated humidity profiling or sequencing is desired.
1.4.2
Computer / Control System Configuration
Reference Drawings 95D39903, 95D39904 & 905
The Computer Control System consists of the following key components:
1) Embedded Computer system, consisting of:
a) CPU card
b) 8 channel, 16
bit A/D converter card with signal conditioning
c) Memory Card
d) Liquid Crystal Display driver card
e) Solid State Relay Board
2) 256 x 128, backlit, dot matrix Liquid Crystal Display (LCD) module
3) 16 key front panel keypad
1.4.2.1 Central Processing Unit (CPU)
Reference Drawing 95D39903
The Central Processing Unit (CPU) consists of a microprocessor, along with all supporting
hardware required to interface with the other devices. During the humidity generation
process, the CPU executes programming designed to control the parameters needed to
generate humidity, such as pulsing heaters and operating valves. Virtually all functions of the
system are controlled by this CPU which is responsible for system timing, user interfacing,
information display, and parameter control.
The CPU also retrieves measured temperature and pressure data from the A/D, which it uses
to calculate frost point, dew point, parts per million by volume, parts per million by weight
and relative humidity. Once calculated, this and all other pertinent information is sent to the
Liquid Crystal Display for real time numeric display. At given (user definable) intervals, the
CPU also sends this data to the printer, if enabled, for hard copy output.