Peter Gluck has been babbling on about how it is impossible to make a mistake with a flow meter. I pointed him to a handy guide to flow meters from Omega, which he then ignored. Anyway, let me point it out here, because it is handy. If you are going to work with flowmeters you should read this carefully. I wish I had read it more carefully years ago. This is a guide to industrial flow meters, but a person using laboratory meters will benefit from reading it.
http://www.omega.com/prodinfo/flowmeters.html
Below are some quotes from it.
If you deliberately install a flowmeter with one of these parameters wrong, such as bubbles for a meter not designed for them, or "whether the flow can reverse" (Defkalion's trick), you get the wrong answer. As you see, there are many ways to do this wrong.
QuoteFluid and flow characteristics
The fluid and its given and its pressure, temperature, allowable pressure drop, density (or specific gravity), conductivity, viscosity (Newtonian or not?) and vapor pressure at maximum operating temperature are listed, together with an indication of how these properties might vary or interact. In addition, all safety or toxicity information should be provided, together with detailed data on the fluid's composition, presence of bubbles, solids (abrasive or soft, size of particles, fibers), tendency to coat, and light transmission qualities (opaque, translucent or transparent?).
Pressure & Temperature Ranges
Expected minimum and maximum pressure and temperature values should be given in addition to the normal operating values when selecting flow meters. Whether flow can reverse, whether it does not always fill the pipe, whether slug flow can develop (air-solids-liquid), whether aeration or pulsation is likely, whether sudden temperature changes can occur, or whether special precautions are needed during cleaning and maintenance, these facts, too, should be stated.
The sections on "Piping and Installation Area" and "Flow Rates and Accuracy" shows many more ways to screw up. As I said, if you are a nefarious person and you want to get the wrong answer, this guide is a bonanza of information on how to cheat.
QuotePiping and Installation Area
Concerning the piping and the area where the flow meters are to be located, consider: For the piping, its direction (avoid downward flow in liquid applications), size, material, schedule, flange-pressure rating, accessibility, up or downstream turns, valves, regulators, and available straight-pipe run lengths. The specifying engineer must know if vibration or magnetic fields are present or possible in the area, if electric or pneumatic power is available, if the area is classified for explosion hazards, or if there are other special requirements such as compliance with sanitary or clean-in-place (CIP) regulations.
Flow rates and Accuracy
The next step is to determine the required meter range by identifying minimum and maximum flows (mass or volumetric) that will be measured. After that, the required flow measurement accuracy is determined. Typically accuracy is specified in percentage of actual reading (AR), in percentage of calibrated span (CS), or in percentage of full scale (FS) units. . . .
All these factors are why you need a licensed HVAC engineer to do this kind of measurement. There is no reason to think that some guy with a degree in nuclear engineering such as Penon will know how to do this job correctly. He didn't know. He made many mistakes that a professional would not make. Either that, or he and Rossi deliberately did it wrong.
