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VMIVME-3126A High Resolution, Isolated Analog-to-Digital Converter Board
Open Transducer Detection
The ADC supplies software controlled open transducer detection. Open transducer
detection allows the user to check if an input transducer is still connected or an open
condition has occurred. This function only works on ranges from ±1 V (0-to-1 V) to
±5 mV (0-to-5 mV). If the transducer connection has opened, the output for that
channel will read positive full-scale (
0xFFFF
in offset binary or
0x7FFF
in two’s
complement). The user sets the
Open Sensor
bit in the desired CSR’s and follows the
rule for reconfiguration. The DSP will determine if the selected channels have open
sensors. Status will be displayed in the PFS register and the
Open Sensor
bit reset in
each CSR.
Filtering
Digital filtering is done in the DSP. The filter setting in each channel’s CSR is stored
and used to restore the proper filter coefficients which are applied in real-time.
The filter approximates a 6
th
order bessel response. For the best performance, use the
lower filter settings on the lower ranges. For example, using the 0.05 Hz filter on the
±50 mV scale considerably reduces the noise spread.
The digital filter for each channel is zeroed after a reconfiguration of that channel.
This puts the filter in a known state and eliminates illegal filter states. Depending on
the selected frequency, there will be a delay after reconfiguration while the filter
settles to the signal present on the inputs.
OPTO Isolation
Optical Isolation is provided on every signal going to or coming from each channel.
These signals consist of the ADC control signal, ADC output, and the input autozero
switch.
DC-to-DC Power Converters
Each channel has a dedicated DC-to-DC Converter. The DC-to-DC Converters are
powered by the 5 VDC power bus at the P1 and P2 connectors. The output
of each converter is 33 mA at
±
15 V. Input-to-output isolation of >1500 VDC maintains
channel to VMEbus isolation.
Current Loop Termination Option
For the current loop termination option, a 400
Ω
resistor is added between the HI and
LO inputs on the board. The resulting voltage from the current flowing through the
resistor is digitized and stored in RAM. The actual current would then be determined
by the user, converting the digitized code into a voltage for the range selected and
dividing by 400.
CAUTION:
Currents greater than 25 mA are not supported and could cause
component failure.
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