Chapter 8: Theory of Operation
Block-Level Theory
8–4
Power S
upply Assembly
The ac input to the power supply is 100–240 Vac, +/-10%. Maximum input power is 440W. The
ac input frequency is 47 to 440 Hz.
Filtered voltages of +5.1 V, –5.2 V, +12.2 V, 3.3 V, and –12.2 V are supplied and distributed
throughout the oscilloscope.
FPD Monitor Assembly
The monitor is a thin film liquid-crystal display (TFT-LCD). This FPD is an 8.4-inch diagonal,
640 by 480 pixel VGA Color Monitor. The assembly requires +3.3 V and +12 V from the power
supply.
A twin fluorescent back light provides illumination for the LCD. The Backlight Inverter assembly
converts the +12 V to +300-1000 volts (acrms) and drives the back light.
Acquisition System
The acquisition system includes four attenuator assemblies on four channel oscilloscopes and
two attenuator assemblies on two channel oscilloscopes on the acquisition board. The
attenuators condition the signal, which is then digitized and stored by the acquisition board. The
graphics board provides the system control interface from the motherboard, and also interfaces
the acquisition board to the display board for display of the acquired data. More detailed theory
on the acquisition system follows this top-level block theory.
Attenuators
The attenuators provide the appropriate impedance matching and all the attenuation and gain
selection for each input channel. The attenuators are part of the acquisition board.
Front Panel
The front panel is read and controlled by a micro controller IC. This device contains a
microprocessor, RAM, ROM, and a DUART for communication with the microprocessor on the
main assembly. The micro controller is located on the keyboard and communicates with the
system control circuitry through an RS-232 cable. It reads the keys and knobs and controls the
LED indicators.
The elastomeric keypad has 30 keys, all dedicated to a single function to improve ease of use. A
conductive element on the inside of each key shorts a gap on the underlying keyboard circuit.
The keyboard controller detects this short and sends the proper keypress information to the
system controller on the motherboard.
There are eleven dedicated knobs. Each knob controls a mechanical encoder. The output of the
encoder is a 2-bit gray code that is read by the micro controller for direction and distance turned.
A pushbutton controls the power through a Remote Inhibit sense line that is routed to the power
supply.
Disk Drives
The floppy disk drive is a 1.44 Mbyte, MS-DOS compatible. It is located on the front panel. The
disk drive can be used to load a new oscilloscope operating system or to load application-specific
software.
The hard disk drive is a high-capacity, shock-resistant unit. It is used to store the oscilloscope
operating system and certain system configuration data.
Either drive can also be used to store and recall oscilloscope setups and waveforms.
To Next Page
Loading...
Need help?
General
