Most likely the best defense against passive/logger monitoring devices is available in the form of any GPS blocker.
Following retrieval the device is usually mounted on a personal pc and the information is downloaded in a data base that is provided by the device manufacture. These are attached to a car or individual and after a certain amount of time they must be retrieved. These devices can be as small as any matchbook and can be hidden just about anywhere. This revolutionary product is also the most difficult to identify and defend against. The best is called a unaggressive or logger monitoring device. There are basically two types of Gps tracking system technology open to the public. Granted there are lawful restrictions about how and when you should use the new monitoring technology however detecting GPS tracking models can sometimes be challenging. The reply is that there really is no privacy.
Which make you wonder what happened to personal privacy. Whereby traders have the ability to send location data even with the battery removed. Furthermore almost all new cell phones have got GPS monitoring capabilities built in to them.
In the Plant i work on, one particular straightening vane was not installed according to the API code during the design in 1996 and to this day, the flow is always inaccurate.The new GPS auto monitor technology allows just about anyone to monitor anyone else. I have also used straightening vanes just downstream bends and valves, but they, too, require placement according API codes.
Later, when i measured the flow at both places, using a portable ultrasonic flowmeter, the values were approximately 30 m3/hr apart and it turned out that the value measured by the vendor was right. The result was that i had to get scaffolding constructed at another location where the distance was sufficient. I had to hire an instrumentation contractor to measure the flow and he, outright, refused to take any readings at that point. The minimum distance was just under 3 pipe diameters. There was a flow rate i had to measure - there wasn't a flowmeter on the pipeline, nor did i have access to a portable one at the time. My experience is that the distance is very important for the accuracy of the reading, to get reliable results, it is recommended that it is followed. The same reasoning applies for control valves.
However I have always seen that it is possible to improve the layout with some out of the box thinking at least to some extent, before sacrificing the accuracy. If your layout does not permit such luxuries, you may fit flow straighteners or flow conditioning devices, immediately after the previous upstream fitting, as a remedial measure. especially after fittings such as elbows, (or double elbows in some cases). You should realise that the straight lengths especially on the upstream side of the orifice is to stabilise the flow and eliminate swirls etc. There are many published data you can get by using a search engine better still there are many books & manufacturers’ catalogues that can throw more light on the area of your interest.Īn instrumentation engineer would refuse to accept these values as it, as they are very finicky about the accuracy of the measuring instrument! However if you can sacrifice the accuracy say to ± 8% or more you can reduce the straight lengths even to 5D by 2D (using your nomenclature)!
For higher values of B, these values are even higher.Īll that will happen if you reduce the straight distances is that the accuracy of measurement will be affected. The value you have quoted is for a very low B of less than 0.3, and that too is the bare minimum.
( B is the ratio of the diameter of the orifice to the internal diameter of the pipe). The straight lengths upstream / downstream of the orifice depend on what is known as (beta) B value.