VXI VT1422A - Manual (Page 158)

156 Programming the VT1422A for Data Acquisition and Control Chapter 4
NOTES
1. When OTD is enabled, the inputs have up to 0.2 µA injected into
them. If this current will adversely affect the measurement, but
checking for open transducers is still desired, enable OTD, run the
algorithms, check analog input variables for measurement values that
indicate an open transducer, then disable OTD and run the algorithms
without it. The VT1422A’s accuracy specifications apply only when
OTD is off.
2. When a channel’s SCP filtering is enabled, allow fifteen seconds after
turning on OTD for the filters capacitors to charge before checking
for open transducers.
To enable or disable Open Transducer Detection, use the
DIAGnostic:OTDetect[:STATe] <enable>, (@<ch_list>) command.
•
The <enable> parameter can specify ON or OFF.
•
An SCP is addressed when the <ch_list> parameter specifies a
channel number contained on the SCP. The first channel on each SCP
is:
0, 8, 16, 24, 32, 40, 48, and 56.
To enable Open Transducer Detection on all channels on SCPs 1 and 3:
DIAG:OTD ON, (@100,116)
0 is on SCP 1 and 16 is on SCP3
To disable Open Transducer Detection on all channels on SCPs 1 and 3:
DIAG:OTD OFF, (@100,116)
More On Auto Ranging
There are rare circumstances where an input signal can be difficult for the
VT1422A to auto range correctly. The module completes the range selection
based on the input signal about 6 µs before the actual measurement is made
on that channel. If, during that period, the signal becomes greater than the
selected range can handle, the module will return an overflow reading
(±INFinity).
To fix this problem, use the DIAGnostic:FLOor <range>,(@<ch_list>)
command. Include the problem channel(s) in <ch_list> and specify the
lowest range desired for auto range to select for those channels. This will set
a range "floor" for these channels that auto range can’t go below while still
allowing auto range to select higher ranges as necessary. If more than one
range floor needs to specified for different channel sets, execute the
DIAG:FLOOR command multiple times.
The DIAGnostic:FLOor:DUMP command sends the current range floor
settings for all 64 channels to the FIFO. Use DATA:FIFO:PART? 64 to read
these values.
The auto range floor settings remain until another DIAG:FLOOR command
changes them or a *RST resets them to the lowest range for all channels.