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4.2.2 16-Channel Multiplexed Mode
In this mode (Figure 14), the 8020-59 will 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 16 (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), 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) 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 read the temperature of the transducer. When this reading is ready (<100ms
later), the VALID output will again go high (5V), indicating that the voltage and current
outputs (now proportional to temperature) are at VOUT and IOUT and are ready to be
acquired. When the host DAS again brings CLOCK low (0V) and then HIGH (5V), the
8020-59 and multiplexer increment to channel 2 of 16 and this reading sequence starts
over again. This reading sequence may be used for up to 16 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 16 Vibrating Wire transducers with thermistors
may be multiplexed into a single DAS.
Figure 14 - Control Signal Sequence: 16-Channel Mode (Channels One and Two Only)
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