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VT1529A/B Verification & Calibration 475Appendix C
Test V-8: Internal
Shunt
Description This test verifies the operation of the internal 50 kΩ shunt resistor and the
associated switches in the VT1529A/B.
Switch operation can be verified by observing the changes in the bridge
output voltage when internal shunt calibration is disabled and enabled.
The bending half-bridge strain path is configured and the Dummy Load is
attached. With the internal shunt disabled, the bridge output voltage should be:
V
sense
= V
excitation
* (10 / (10 + 7.5) - 0.5)
With V
excitation
= 2.0 V, the expected value of V
sense
is 0.142857 V.
With the internal shunt enabled, the bridge output voltage should be:
V
sense
= V
excitation
* (10 / (10 + R) - 0.5)
Where R equals the parallel combination of the 7.5 kΩ resistor in the
Dummy Load and the 50 kΩ internal shunt or 6.522 kΩ. Again, with
V
excitation
= 2.0 V, the expected value of V
sense
is 0.210526 V.
Figure C-5. Signal Path for Shunt Cal Resistor Port Test
10K
Buffer
To VT1422A
(VT1539A SCP)
X2
Buffer
RJ-45
X2
2:1
Mux
Cal-
Cal+
8-pin Telcom
Connector (RJ-45)
Cal-Cal+
350
120
customer
10K
10K
10K
+
-
Optional
Filter
2,10,100Hz
+Excitation Sense
Instrument.
Amplifier
Dynamic Strain
Output
+ Excitation
- Excitation
Internal
Rcal
50K
Local Rcal
Enable
Remote Rcal
Enable
Int/Ext Rcal
Select
Excitation Sense
from
C
Hs 1-
3
1
32:1
Mux
CH31
CH00
CH01
32:1
Mux
CH31
CH01
CH00
Bridge Sense
from
C
Hs 1-
3
1
External customer
shunt cal resistor
terminals
-R Cal
+R Cal
Current
Limit
Excitation
to CHs 1-7
enable excitation
CHs 0-7
+Excitation
+Sense
-Sense
-R Cal
+R Cal
+Excitation Sense
-Excitation Sense
-Excitation
Wagner
Voltage enable
off for full bridge
-Excitation Sense
X16
Pin 5
Pin 4
Pin 2
Pin 7
Pin 6
Pin 3
Pin 8
Pin 1
10K
Dummy Load
7.5K
1k