Strain measurement - NI9237 output units

[LVPoland]

Hello,

I have some problems with strain measurement. Daq assistant is configured as strain, but what is the output unit in LabView? W have same values described as "u" - it is uV? uV/V? or maybe something else?

I have to do some calculations, but output voltage from wheatstone bridge (full brigde) is different for constat strain from DAQ readings, but all parameters are set properly.

Can anyone help me?

[Blokk]

Please post your VI as a snippet ( http://www.ni.com/tutorial/9330/en/ ) or as a VI attachment. You more likely get help if people can see your code...

[Jacobson-ni]

We would need to see your code to be certain, but if you have configured the channel to read strain measurements it should be returning strain which doesn't have a unit if I remember correctly.

http://zone.ni.com/reference/en-XX/help/370469AC-01/lvdaqmx/mxcreatechannel/#DAQmxCreateChannel(AI-S...

[LVPoland]

Jacobson,

Thank you for reply. Strain returned from LV is without unit - now it is clear.

Now have another problem, not related with labview directly. Strain gauges are sticked to my specimen like in the attachment (axial strain only, but in my configuration R1 and R3 are active). I performed simple test on durability machine - applied axial load on my specimen (cylinder tube) - 3kN, 4kN, 5kN and the LabView acquire three values of strain - 100u, 133u, 166u.

But durability machine acquire at the same loads three deflections: 0,11mm(at 3kN), 0,135mm(at 4kN), 0,16mm(at 5kN). Dividing it by specimen height (294mm) calculated strains are: 3,74*10-4, 4,59*10-4 and 5,44*10-4, so 374u, 459u, 544u. Can anyone explain me, why this values are not equal?I can't understand it 😞