Fluke 2680A, Руководство по обслуживанию

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Theory of Operation
Module Power Supply PCA (268XA-4031)
2
2-11
Display Interface
The display controller interface on the backplane consists of a tri-stateable
levelshifter/buffer, some decoupling capacitors, and the display ribbon cable connector
(P8). The levelshifters (U1, 2, 3) need to be tri-stateable because, when the
microprocessor is talking to the calibration EEPROMs, the display should not receive
those transmissions.
Module Interface
The module interface connectors (P1-6) have a number of passive components
surrounding them, these are for ESD protection. The optoisolators that perform the
analog side of the guard crossing are on the 4031PCA. Because each module slot has its
own dedicated channel in the fpga, the only circuitry that is required on the backplane is a
non-inverting buffer (U4) to clean up the edges of the UART receive signals that come
from the in-guard system.
Module Power Supply PCA (268XA-4031)
The module power supply PCA contains all of the analog side of the guard crossing
hardware. It is located with each module’s housing, as a daughter card that plugs into a 2
row, 10 pin header on the module. The power supply design uses a fully isolated push-
pull topology, driven from a differential 393 kHz clock source. There are 3 regulated
outputs that power the in-guard 5.2 V (Vdd), -5.2 V (Vss) and +5.6 V (Vddr),
each one is derived from a dedicated linear low dropout regulator (U5, U6 and U4,
respectively). The isolation transformer, which is rated at 300 V Category 2, is made of
circuit board traces on two separate boards, primary coil on the 4031 and secondary coil
on the 4032, coupled together by a core that runs through the 4031 PCA and around the
4032 PCA.
The only other circuitry in addition to the power supply itself on the 4031 board are the
optoisolators (U2 and U3) and the calibration EEPROM (U7). U2 and U3 on the 4031
PCA are the bridge for the UART communication signals that run between the fpga on
the 4004 PCA and the in-guard microcontroller. U7 is a 2Kbit serial EEPROM
addressable from the out-guard microprocessor (MPC855T, U6 on the 4004 PCA) via an
SPI bus that runs on the Backplane PCA (4001).
Digital Input/Output PCA
The following paragraphs describe the digital input/output as follows:
•
Microcontroller
•
Digital Input Threshold
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Digital Input Buffers
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Digital Output Drivers
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Relay Output Drivers
•
Totalizer Input
•
Totalizer Enable