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In auto mode, the PM-ADC-IB/PT-ADC-IB detects whether a usable external reference is
present or not. If it is able to lock to the reference, it will operate as described in
External mode; however, if the reference is lost or becomes unusable, the PM-ADC-IB/
PT-ADC-IB will automatically switch over to operate as described in Internal Mode. If the
reference is restored, the board will again automatically switch over to operate as
described in External Mode.
Analog Level Detection
Analog input level detection is provided in two forms:
The first implementation is through the use of rectifier and comparator circuits that are
used to detect a user-defined minimum signal amplitude. This minimum amplitude is
conveyed via a nonvolatile, digitally controlled potentiometer that provides the
reference voltage to the comparators. (The reference voltage can be individually set for
channels A and B on all inputs.) If the amplitude of the input signal exceeds the
comparator reference voltage, the green LED for that channel is illuminated.
If the signal level falls below the minimum threshold for a user-defined time duration,
the sampled data output from the A/D converter will be overwritten by all zeroes within
the FPGA. This greatly reduces idle channel noise in systems using A/D and D/A
converters. Conversely, the detection of a signal above the minimum threshold value
also has an associated time duration before muting is released, providing hysteresis to
this function.
The second implementation of analog level detection is performed in the A/D converter.
When the analog level exceeds the digital full-scale capability of the converter, the red
Clipping LED for that channel is illuminated, and the condition is reported to the control
system. The user has the option of defining whether this condition constitutes an
alarm.
Back Panel I/O Module for PM-ADC-IB/PT-ADC-IB
The PT-A2-BP back panel I/O module corresponds to the PM-ADC-IB and PT-ADC-IB
modules. DB-44 connectors are used on the PT-A2-BP. The optional PT-A2-DTB terminal
block adapter is available to accommodate wiring of individual signals to the frame.
Platinum Frames and Modules
Installation, Configuration, and Operation Manual
105
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