92 Programming the VT1422A & VT1529A/B for Remote Strain Measurement Chapter 3
Built-in Strain Conversion Equations
When using the VT1422A’s built-in strain conversion
(SENSe:FUNCtion:STRain:<bridge_type> <range>,(@<ch_list>)),
the following equations are used to convert voltage to strain.
Full Bridge Equation
(bridge_type=FBEN)
This equation is used by the VT1422A to convert bridge measurements to
Engineering Units of Strain for channels specified in the command
SENSe:FUNCtion:STRain:FBEN <range>,(@<ch_list>).
where: Vmeasured = measured voltage value
Vexcitation = excitation voltage
Vunstrained = unstrained voltage
gFactor = gage factor
Half Bridge Equation
(bridge_type=HBEN)
This equation is used by the VT1422A to convert bridge measurements to
Engineering Units of Strain for channels specified in the command
SENSe:FUNCtion:STRain:HBEN <range>,(@<ch_list>).
where: Vmeasured = measured voltage value
Vexcitation = excitation voltage
Vunstrained = unstrained voltage
gFactor = gage factor
Quarter Bridge Equation
(bridge_type=Q120, Q350
or USER)
This second-order equation is used by the VT1422A to convert bridge
measurements to Engineering Units of Strain for on-board strain SCP
channels only. Because VT1529A/Bs can expand the VT1422As strain
channel count to 512, use of this non-linear strain conversion equation
would require too much VT1422A memory. Instead, a quadratic
approximation of this equation is used. See below. For the following
equations, Vi = bridge output while strained, Vu = bridge output unstrained
and Ve = excitation voltage at the bridge.
Quarter Bridge Equation for Strain SCPs only
Quarter Bridge Equation for VT1529A/B only
Strain Vmeasured Vunstrained
()gFactor Vexcitation
×()=
Strain 2Vmeasured Vunstrained
()gFactor Vexcitation
×()×=
Strain 4Vr
GF 12Vr
()
-------------------------------
=WhereVr
ViVu
Ve
-----------------
=
Strain a2Vi2a1Via0
++=
Where a28
GF Ve
2
×
---------------------, a1
44VuVe
()
GF Ve
2
×
-------------------------------- , a0
42Vu
2VeVu
()
GF Ve
2
×
------------------------------------
===