@Max The Magnificent - how do I submit the blog on the inexpensive pressure gage? It includes a NI LabVIEW VI and an Excel program. Do your readers care if the spelling is gage or gauge, or is that a topic for another discussion? :-)
@Les Hammer: The worst unit that we have gets about 11% linearity error. I haven't correlated linearity to how much glue was slopped on the strain gage. I could send you more details later.
Please do. I'm interested in hearing about things like the length and diameter (and thickness and material) of the pipe -- also the end cap -- the type and cost of the strain gauge -- what effect (if any) does pre-presurizing the pipe have.... inquiring minds want to know these things...
Actually the disc on the end of a pipe pressure measurement is an experiment that we do at the Colorado School of Mines. We have 12 units built up and connected up in parallel to a commercial Omega unit. We run a LabVIEW program to take data from both - using the Omega as a reference, then we analyze in Excel. The worst unit that we have gets about 11% linearity error. I haven't correlated linearity to how much glue was slopped on the strain gage. I could send you more details later.
@Les Hammer: Measuring pressure cheaply - weld a disk on the end of a pipe. Seal the pipe if you want the air that is in it to be your reference. Glue a strain gage to the disk. The strain will change with the chaging air pressure.
Clever! I'd be interested in seeing a blog on this with a reference design showing the accuracy and resiolution that could be achieved with such a design. Are you interested in writing such a column?
RE: Ultra sonic sensor calibration - the speed of sound is proportional to the square root of the temperature in Kelvin. You will need to take that into account.
RE: Measuring pressure cheaply - weld a disk on the end of a pipe. Seal the pipe if you want the air that is in it to be your reference. Glue a strain gage to the disk. The strain will change with the chaging air pressure.
1. Water pressure. Actually differential h2o pressure with absolute pressure of 40 to 60 psi would be great.
2. Air pressure. Absolute air pressure between 30 - 50 psi.
Having a tough time finding either of these sensor that are afforable. Say around 5 bucks ... less would be better. I've found some in the 35 to 100's of dollars. I'd like to have digital output for input to an Arduino.
There much be a cheap way to measure pressure. Medical devices are very low pressures but I would think the auto industry would have devices in the ranges above. I just can't find them.
@David: ....but this xufeifei is posting stuff all over EET...
Bummer -- I'll see what I can do about that.
Mom is great -- I'm at my brother's house -- she will be round here in about 30 minutes -- we'll take a stroll to the shops at the bvottom of the road -- tomorrow I'm going wo her writing club with her -- it's great being over here and not working 12 hours a day :-)