VXI VT1422A, User Manual

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180 Advanced Programming with the VT1529B Chapter 5
When a VT1529A/B scans through a list of channels, it stays on the last
channel in the scan list for that VT1529A/B until the unit is scanned again.
To minimize the “soaking” effect, have a low voltage or a short on the
low-level inputs on this last channel.
3. Reduce “switching crosstalk” by increasing time between channels .
Increasing the time between channel measurements will give the
VT1529A/B more time to settle. In the worst case, when all but one channel
soaks the system with 80% of full-scale input voltage (0.4 V) and the system
remains on this soaking voltage between scans, the VT1529A/B can settle
to within about 4
µ V in 40 µ s. Note that this is within the offset spec of 2 µ V
within 100 µ s. For best accuracy, scan at the slowest rate that is acceptable
for that particular application.
The graph below shows the worst-case scenario for the VT1529A/B. As
stated earlier, if only one channel is 80% of full scale, the switching
crosstalk is barely measurable. Most system configurations do not approach
the worst-case scenario.
Typical offset error due to "soak" voltage
-6
-4
-2
0
2
4
6
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
Sustained "soak" voltage on low-voltage inputs
Offset erro
r (µ
V)
40usec
100usec
200usec
500usec