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4.2.3 32-Channel Multiplexed Mode
In this mode (Figure 15), the 8020-59 will also excite and provide output only when told
to do so from the host DAS. As soon as the 8020-59 is powered, if ENABLE and
CLOCK are low (0V), the 8020-59 will go to "sleep" and will wait for commands from
the host DAS, drawing less than 10μA from the +12V system power supply (16.5mA if
using a +24V system power supply).
When a reading is to be taken, the host system first brings ENABLE high (5V) to enable
the 8020-59 and then CLOCK high (5V) to activate channel 1 of 32 (for control signal
timing requirements, refer to the model 8032 Multiplexer Instruction Manual). The 8020-
59 will "wake up" and read the transducer connected to channel one of the multiplexer.
When the reading is ready (approximately one to two seconds later (typ)), the 8020-59
will bring the VALID output high (5V), indicating to the host DAS that the voltage and
current outputs (proportional to the digits of transducer number one) are at VOUT and
IOUT and are ready to be acquired.
Once the reading is acquired, the host system brings CLOCK low (0V), and then high
(5V) again to increment the 8020-59 and multiplexer to the next transducer. When this
reading is ready ( approximately one to two seconds later), the VALID output will again
go high (5V), indicating that the voltage and current outputs (proportional to the digits of
transducer number two) are at VOUT and IOUT and are ready to be acquired. This
reading sequence may be used for up to 32 transducers.
When the final transducer has been read, the host DAS brings CLOCK and ENABLE
both low (0V) to reset the system. The 8020-59 will go back to sleep until it is time for
the next reading. Using this feature, up to 32 Vibrating Wire transducers may be
multiplexed into a single DAS.
Figure 15 - Control Signal Sequence: 32-Channel Mode (Channels One through Four Only)
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