Built-In Strain Conversion Equations - VXI VT1422A User Manual

Built-in Strain Conversion Equations

Full Bridge Equation
(bridge_type=FBEN)
Half Bridge Equation
(bridge_type=HBEN)
Quarter Bridge Equation
(bridge_type=Q120, Q350
or USER)
92 Programming the VT1422A & VT1529A/B for Remote Strain Measurement
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.
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>).
(
Strain = V
measured
where: V
measured
V
excitation
V
unstrained
gFactor = gage factor
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>).
× (
Strain = 2 V
measured
where: V
measured
V
excitation
V
unstrained
gFactor = gage factor
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, V = bridge output while strained, V
i
and V = excitation voltage at the bridge.
e
Quarter Bridge Equation for Strain SCPs only
4V
r
------------------------------ -
Strain =
(
GF 1 2V –
Quarter Bridge Equation for VT1529A/B only
2
Strain = a V + a V
2 i 1
8
-------------------- - , a
Where a =
×
2
GF V
) ⁄ (
– V gFactor
unstrained
= measured voltage value
= excitation voltage
= unstrained voltage
) ⁄ (
– V gFactor
unstrained
= measured voltage value
= excitation voltage
= unstrained voltage
u
V –
i
---------------- -
WhereV =
)
r
V
r
+ a
i 0
(
– 4 4V – V
u
-------------------------------- , a
=
×
1
2 2
GF V
e e
× )
V
excitation
× )
V
excitation
= bridge output unstrained
V
u
e
) (
2
4 2V – V
e u e
----------------------------------- -
=
×
0
2
GF V
e
Chapter 3
)
V
u