I have to calculate the total uncertainty for a compressor test-rig, so i am measuring static pressures, total temperatures, mass flow. I am using the following modules for each of the variables mentioned:
Pressure: NI 9203 (transducers) and Ni 9265 (pressure reducer)
Temperature: Ni 9211
Mass flow: NI 9203
So I have to incorporate in the total uncertainty the acquisition system uncertainty.
In the catalogs for each of the modules i found the following values
Ni 9203: Gain error +/-0.04% offset error +/-0.02
Ni 9265:Gain error +/-0.05% offset error +/-0.02
Ni9211: Gain error +/-0.05% offset error +/-15 uV
My question is about how to incorporate all this errors in the proagation of uncertainty calculation:
U(95)=((b1*theta1)^2+(b2*theta2)^2+....)^(1/2)
b1 are the errors due to each of the variables
theta is the derivative of the function for each one of the variables
According to this paper from asme http://www.barringer1.com/drbob-bio_files/ASME83.pdf which is based on th ASME PTC 19.1, which I haven't been able to get it.
The uncertainty is divided in two components bias and random errors, then each one has to be computed and in the end add all this together.
U(95)=(B^2+P^2)^(1/2)
So what i am doing is to get all the bias components from the sensors and also from the module of each sensor and adding them
Btotal=(B1^2+B2^2+....)^(1/2)
Where B1 and B2 are the bias components of the error in sensor , module and so on.
Ptotal=(P1^2+P2^2+....)^(1/2)
Where P1 and P2 are the random components of the error in sensor , module and so on.
then I am applying the propagation equation taking into account each component
Ubias(95)=((b1*theta1)^2+(b2*theta2)^2+....)^(1/2)
where b1... are just bia component and in I do the same in the other case with the random component
and in the end I sum this quantities
U(95)=(Ubiastotal^2+Pbiastotal^2)^(1/2)
So my question is if the values that i took from the catalogs of each module correspond to the bias component of the error or is a combination of random and bias component?
The other question is related with NI911 this is used for the thermocouples and i was reading in one of the forums that for this module i take the bias error or systematic directly from the figures in the catalogs so for instance if i read 1,8 C for autozero off room temperature, that value corresponds to +/-1,8.
And the last question is if you can help me with a reference book about the equations required to transform from volts to calculate the gain and offset error that you have in the catalogs.
Sorry for the long explanation but i didn't know how to pose the questions in an easier way
Thanks for the help\
Esteban
