This time I will review the specsmanship of a single turbine insertion style meter. Its manufacturer infers the meter’s performance by once again mixing and matching information in an attempt to project its capabilities beyond what is possible, with regard to the meter’s accuracy specifications.
On the product’s specifications document the manufacturer lists the meter’s accuracy capabilities in three ways shown below:
Let’s start with the first statement, which says the meter is +/- 0.5% of reading at the calibrated velocity. My first question is, what is the calibrated velocity? If the manufacturer is not going to state the velocity (and typically a meter is calibrated over a velocity range, not a single point) at which the meter is calibrated, then why make the accuracy statement at all? My guess is that if this meter actually has an accuracy of +/- 0.5% of reading, this occurs at an elevated velocity at which no flow system would ever be designed to operate in the real world.
The second statement says that the meter is accurate to +/- 1.0% of reading from 3 to 30 ft/s, which appears to be reasonable and straightforward. It defines the meter’s accuracy in easy to understand terms with an associated turndown, or as they call it, “range.”
However, the third statement completely invalidates the second when it says the meter is +/- 2.0% of reading from 0.4 to 20 ft/s. If the second statement was true, then this statement should say that the meter is +/- 2.0% of reading from 0.4 to 3 ft/s. I am willing to bet that this meter really only offers +/- 1.0% of reading accuracy from 20 ft/s to 30 ft/s, and below 20 ft/s the meter is +/- 2.0% of reading accurate.
Now, if this isn’t confusing and misleading enough, the manufacturer goes even further to state the meter’s accuracy with the table below (which, by the way, reinforces the third accuracy statement and further invalidates the second accuracy statement):
In this case they make a straightforward statement: “Operating Range for Common Pipe Sizes 0.17 to 20 ft/s.“ However, they add that the “accuracy of +/- 2.0% begins at 0.4 ft/s”. So, what is the flow rate at 0.4 ft/s for any given pipe size? Because the manufacturer only states the operating range in gallons per minute (GPM), the reader has to know how to calculate the flow rate from the velocity to determine where the +/- 2.0% accuracy really begins.
I have generated a chart similar to theirs, listing their flow range and the calculated flow range where the +/- 0.2% of rate accuracy is applicable.The values shown in blue are where the flow rate attains a velocity of 0.4 ft/s. I have also listed the formula at the bottom of the table, which shows how GPM is calculated knowing the velocity and pipe diameter or size.
To make matters even worse the manufacturer changes how they mix and match information depending on which flow technology they are presenting. This single turbine insertion style meter is the second technology I have analyzed (the first technology analyzed was the insertion magmeter presented in Part 2). Next, in Truth In Specsmanship Part 4, I will present the inline magmeter as my third example, which again twists specifications to infer a higher level of performance and deceive the consumer.