SERIES
9900
SECTION V I I I
SERIES-9900
THEORY OF
OPERATION
9000
SERIES
GAUSSMETERS
VIII-A OVERVIEW
The SERIES-9900 gaussmeter is housed in a standard VME-style
cabinet/card cage. All cards and
probe interface modules
plug into a
common, custom (non-standard) backplane via standard 32-, 64- or 96-pin
DIN connectors. Also mounted on the backplane are the RS-232, IEEE-488
and ANALOG OUTPUT connectors. The backplane has no active
components.
VIII-B POWER SUPPLY
Refer to the block diagram in Figure VIII-A. The power supply section of the
SERIES-9900 gaussmeter consists of two electrically-isolated supplies; one
for the digital section and the other for the analog
(probe interface module)
section. Each section has its own line voltage step-down transformer. The
components for both supplies, with the exception of several high-current
bridge rectifiers and the transformers, reside on the
power supply control
card
in the card cage. Interconnection between this card and the
transformer/rectifier assembly is accomplished with a multiple contact, high
current connector. Power is routed to each section via the backplane.
The digital supply is used primarily by the
processor card
and
peripheral
control card,
and by optocoupler components in each
probe interface
module.
The supply delivers 3.0 A at +5.0 V, and is protected by overcurrent
and overvoltage sense circuits.
The analog supply is used primarily by the
probe interface modules
and
de5.0 Vat 1.5 A, ±15 Vat 1.2 A each, and 24 Vac at .15 A at the line
frequency. The +5 V supply is also used by the optocoupler components on
the
peripheral control card.
The +5.0 V supply is protected by an overcurrent
sense circuit. The +15 V supply tracks the -15 V supply.
Linear designs are used throughout to provide low ripple power to those
sections responsible for conditioning the low-level signals associated with
Hall devices and the high-resolution A/D converters. To reduce ground loop
and ground noise problems, each module slot and digital card location has its
own private power supply lines on the backplane. All return (ground) lines tie
to one common point on the
power supply control card.
Operation from 115 Vac or 230 Vac line voltage is selected by "programming"
the line voltage input receptacle on the rear panel of the gaussmeter, which
reconfigures the electrical arrangement of the primary side of the
transformers. This receptacle also contains the line fuse. The center terminal
of the receptacle is tied to the metal frame of the chassis.
PROCESSOR CARD
On the processor card is a 10 MHz 8088 microprocessor, 128k bytes of
program ROM, 256k bytes of dynamic RAM, 512 bytes of non-volatile
EEPROM and the various support components required for timing and
interrupt processing. The 240 x 64 dot matrix LCD is controlled by a graphics
display controller under the direction of the 8088. The display controller uses
an 8k byte static RAM to store screen information. Most components are of
the high speed, low power CMOS type to reduce the demands on the
gaussmeter's power supply.
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