Hi I am Aerospace Engineer with a degree from Iowa State University. This topic is interesting to me due to the fact that aerospace applications, especially wind tunnel testing involves pressure sensors, transducers of various types for generating data that is valuable to later analysis
We have a sensor that has been specified as 0.08% BSL typical (linearilty, hysteresis and repeatability combined) (0.14% BSL max.). What is the mathematical meaning of this?
This is one of those alternate terms used for best-fit straight line. In my slide 12, you'll know it is actually an eye-ball identification. The equation would be similar to slide 11 but slightly more difficult to detemine exactly. This is why suppliers often used the least squares best fit, since it has a mathematical representation. Many suppliers explain their methodology in an application note. You might want to see if this is the case for your supplier.
Most sensors are processor integrated. arnt these proporties more dependent on sofware vs hardware?
Sensors that have integrated digital processing and signal conditioning have both the hardware and software to improve on the basic (inherent) properties of the transducing element. If not properly applied, they can add more inaccuracy. In many cases, these are smart sensor that we will discuss in more detail. As noted, some parameters such as precision (and resolution) cannot be corrected by hardware or software.
We have a sensor that has been specified as 0.08% BSL typical (linearilty, hysteresis and repeatability combined) (0.14% BSL max.). What is the mathematical meaning of this?
Randy, the slides showing difference on accuracy and precision are the best explanation I have seen on the subject. One related thing not covered, and often misunderstood is resolution, i.e. number of bits/digits. Maybe you could discuss in the chat session.
I did not resolution have on the slide but did mention that resolution (specifically for digital output sensors) is impacted by the number of bits of the A/D conversion. It is representative of precision for the digital sensor. The quantization error is reduced by increasing the bit rate and the cost goes up as well. For an analog sensor with a continuous output, precision is a little more straight forward.
I have found the manufacture data sheet is not always correct for individual sensors, so I have to calibrate the sensors I use to verify my software will follow the sensor for the tempurature I work in.
Correlation between supplier and user is frequently an issue in measurements. However, the supplier should be meeting its data sheet. You might want to see if they can work with you to determine why you are observing specifc product outside of their specs. It could save you money.
Are you using live spec sheets? If so which ones and where can we get them to follow in review???
I just went to the Digi-Key website then filtered to sensors/transducers, then pressure and selected from the potential manufacturers. Data sheets on line rarely had an accuracy value specified. In any case, you ned to go to the real data sheet not an on-line compilation that could have typos, to get the real values and technique being used by the supplier.
Some manufacturer's do not offer analog versions of their pressure sensors. I guess a calibration house can submit accuracy numbers at various pressures.
On slide 12 (for a future presentation), might the difference between the two "End Points" (currently labeled "B") be renamed "C" (since the two "B's" are not necessarily the same)?
Good point. As I noted, I sourced the graphic from a manufacturer's website
Randy, the slides showing difference on accuracy and precision are the best explanation I have seen on the subject. One related thing not covered, and often misunderstood is resolution, i.e. number of bits/digits. Maybe you could discuss in the chat session.
@ Dave SD - Often the manufacturer just digitizes her line of analog sensors; and if we consider that digitization does not affect the base accuracy of the analog sensor materially, you can just use the comparable model's analog specs until you hit the ADC q-noise, jitter, DNL, ANL spec limits.
On slide 12 (for a future presentation), might the difference between the two "End Points" (currently labeled "B") be renamed "C" (since the two "B's" are not necessarily the same)?
Most analog pressure sensor specifications include an accuracy spec. However, the digital pressure sensor/transmitters I've seen have specs that do not include an accuracy spec. QA department personnel and Engineering typically require this info, making it difficult to bring in digital pressure sensors.
I have found the manufacture data sheet is not always correct for individual sensors, so I have to calibrate the sensors I use to verify my software will follow the sensor for the tempurature I work in.
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