VXI VT1422A - Manual (Page 179)

Advanced Programming with the VT1529B 177 Chapter 5
Note
The high-level inputs actually use the same excitation voltage measurement
path that is used for strain measurements. This means that there is an
internal 10 k
Ω resistor from each terminal to a common point for each
8-channel block as shown in Figure 5-9. During excitation voltage
measurement of any channel in any bank on a VT1529B, the switches
shown in the Figure 5-9 are closed on all banks, connecting the Bridge
Excitation inputs on the front panel to the input resistors, which will cause a
small current to be sourced to the other channel inputs. During other
measurements, the switches are opened and the resistors become a
connection between all bank + inputs and all - inputs. This connection can
affect the input signal levels unless the inputs are driven from a low
impedance source.
DCV Measurement
Command
Sequence
For the low-level inputs, the input filter needs to be set up and the channels
for voltage measurements need to be linked. The VXIplug&play driver calls
for this are:
hpe1422_cmd(vi, "INP:FILT:FREQ 10");
Set up 10 Hz input filter
hpe1422_cmd(vi, "INP:FILT:STAT ON");
Enable filter
hpe1422_cmd(vi, "SENS:FUNC:VOLT AUTO,(@10000:10005)");
Measure DCV on
low-level inputs on channels
10000-10005
For the high-level inputs, simply link the channels for voltage
measurements. Use the “SENS:FUNC:HVOL” command:
hpe1422_cmd(vi, "SENS:FUNC:HVOL AUTO,(@10008:10015)");
Measure DCV on
high-level inputs on channels
10008-10015
Figure 5-9. High-Level Input Circuit
10k 10k 10k 10k 10k 10k 10k 10k
10k 10k 10k 10k 10k 10k 10k 10k
+ Excitation
- Excitation
High-level DCV Sense
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
Ch. 0 Ch. 7