View source for XPod Bridge - Strain gauge

X-Pod Strain gauge Bridge

OROS analyzers feature optional Wheatstone bridge conditioner. 
[[File:xpod_strain.png|none]]

==Expander modules==
The XPod is a device that can be fixed on OR3X TW analyzer. Each XPod is associated to a block of 8 inputs.


[[File:Xpod-plug.png|framed|none]]
In the connected mode, when and XPod is present each corresponding input can be routed to:

· The BNC input (Standard)

· The XPod connector


===General Xpod settings===

* '''Type''': For acquisition setup preparation, the XPod presence can be simulated in the office mode:

One XPod type selector is available for each XPod position. 
[[File:xpod bridge.png|framed|none]]

* '''Bridge max current''': Select the max excitation current for the corresponding active Bridge Xpod. Each bridge Xpod excitation current can be limited to 30 mA up to 4 V and 12 mA up to 10 V.
* '''Bridge voltage''': Select the excitation voltage for the corresponding active Bridge Xpod. From 0 to 10 V.

===input settings===
[[File:xpod bridge2.png|framed|right]]
For each [[NVGate_Front_End#Inputs|input]], you can select the following options dedidctaed for Xpod gauge:

*'''Type:''' bridge signal conditioning for strain gage. <br>

*'''Gauge type''': Full, Half or Quarter bridge mount. The completion resistors are included in the Xpod.<br>

*'''Resistance''': Bridge completion resistor: 120 or 350 Ohms for quarter bridge mount.<br>

*'''Gain''': Bridge gain: 10 or 100 depending on the required precision and range.<br>

*'''Max current''': the provided current can be limited to 30 mA up to 4 V and 12 mA up to 10 V.<br>

*'''Excitation voltage''': Each Xpod provides an excitation voltage from 0 to 10 V.<br>

*'''Offset Comp.''': Bridge offset comp: Can be used for manual balance of the bridge.<br>

===tutorial: How to set up XPOD conditioners for strain gage===

====Hard Connection====
Let us see how to proceed a half bridge connection.

Use a male SUB D 9 pins connector and a "bullet proof" cable like Ethernet cable to link the strain gages to the connector.

[[Image:Strain_Gage_User_Guide_01.png|framed|none]]

[[Image:Strain_Gage_User_Guide_02.png|framed|none]]

Then weld the connector pins according to the pin-out diagram below:

[[Image:Strain_Gage_User_Guide_03.png|framed|none]]
[[File:full.png]]
[[File:Annotation 2020-04-16 184550.png]]
[[File:Annotation 2020-04-16 184709.png]]


==Set up NVGate==
<font color="#34A9DC">'''Sensitivity'''</font>

In quarter bridge configuration, the gauge is usually glued toward the beam direction to measure the bending for example. In this case the right formula is

[[Image:Strain_Gage_User_Guide_04.jpg|framed|none]]
&nbsp;
[[Image:Strain_Gage_User_Guide_05.jpg|framed|none]]

<font color="#333333">Where

-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; S = Em/V is the sensitivity (*V / µdef)

-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; e , 2, 3 et 4 are the resistivity of the gage or generated by the hardware depending on the type of the

bridge.Here, 2, 3 and 4 are XPOD internal resistors

-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; V, the excitation voltage (in NVGate, the settings is &nbsp;"Expender module/Bridge voltage")

-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ΔEm, the strain measurement voltage

-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; r, equal to R1/R4=R2/R3 often equal to 1.

-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Sg is the gage factor (often equal to 2 x 1E-06 volts per micro-def

{|border="0" cellspacing="2" width="100%"
|<nowiki>-</nowiki> 
|   n, the number of gages (For full bridge, it<nowiki>’</nowiki>s 4. For ¼ bridge it<nowiki>’</nowiki>s 1.)

|}

</font>

You can notice that the sensitivity is not linear with the stress  = L/L. For low strain, the formula is equivalent to:

[[Image:Strain_Gage_User_Guide_06.jpg|framed|none]]

For a half-bridge configuration, it is possible to glue 2 gauges toward the beam direction as shown in the figure below:

[[Image:Strain_Gage_User_Guide_07.jpg|framed|none]]

In this case, the sensitivity is linear and is equal to:

[[Image:Strain_Gage_User_Guide_08.jpg|framed|none]]

So the fact that 2 gages are used instead of only one gets the bridge sensitivity twice better.

<font color="#34A9DC">'''NVGate setup'''</font>

It is advised to first add a "transducer" in NVGate database in order to register the bridge configuration.

Browse'' the Home menu  Transducer tab  Database''

[[Image:Strain_Gage_User_Guide_09.png|framed|none]]

Add a new transducer which is in fact a bridge configuration.

In the ''Conditioner'' area, fill the Gauge bridge type, the gauge resistance, the excitation voltage and so on.

The sensitivity to be filled is the bridge<nowiki>’</nowiki>s one (in red below). So, it is necessary to compute this sensitivity according to the above formula.

<font color="#1F497D">
[[Image:Strain_Gage_User_Guide_10.jpg|framed|none]]
</font>

<font color="#34A9DC">'''Measurement'''</font>

The XPOD contains 8 inputs. In case of XPOD connection, the 8 BNC inputs are disabled for using the XPOD inputs.

These XPOD inputs can be connected to different plug-ins like FFT or Time domain analyzer for example.

Then the bridge has to be balanced through the Bridge Auto-zero feature (this option has to be setup to ON in the Input settings).

[[Image:Strain_Gage_User_Guide_11.jpg|framed|none]]

Press on «&nbsp;Bridge Auto-zero&nbsp;» from the "measurement" tab to start the bridge balancing. This step may last about 30 seconds.

[[Image:Strain_Gage_User_Guide_12.jpg|framed|none]]

Now, the measurement is ready to start.

[[category:Strain Gage User Guide]]

=== download ===
 
[https://orossas.sharepoint.com/:b:/g/support/EerOWioePhdAv8ioRwGCNAYBZe7TmmCnHF-oPxYOQz03Qw?e=KBG1I6 Download : OROS BRIDGE CONDITIONERS XPOD™ CONNECTIONS]

=== See also ===
[[External_tools:_Rosette_computation|Compute Main stress with rosette]]