Insertion type Magmeter? 3

[bioengr82]

The RO supplier for a plant we are building swears that their insertion type magmeters (Signet) are just as good as tube type. I'm not an expert, but I just don't see how this is possible. Given the assumptions needed by an insertion type meter is it even possible to establish a percent accuracy? Does anyone have experience with the two?

Any input is appreciated.

 

[jaimeappolinario]

magmeter is no a good solution, user a magnet flow meter
(tube)

 

[sulphuric]

Insertion type magmeters were specified in a plant I was involved with back in the late '80's. They were specified as a less expensive alternative to tube type magmeters. One service was concentrated sulphuric acid where they were eventually replaced with tube type. The insertion type did not have the correct materials of construction for the service. Another service was cooling water return to a four cell cooling tower where they were used to balance the flow between the cells. The mounting nozzles were too long initially and the probe wasn't even in the flow stream. This problem was eventually corrected and they provided only general indication of flow rate. I would not use them if you wanted to accurately meter a fluid.

 

[bioengr82]

Thanks sulphuric. Those were some of our general worries, and it is good to have them confirmed by the voice of experience. I think it will end up a compromise for cost purposes; use insertion on some of the less important metering points and insist on a tube magmeter at the effluent and influent.

jaimeappolinario-
I belive they are both magnet flow meters operating on the same basic principle. I refer to both as 'magmeter'.

 

[semo]

I recently tried to utilize the Krohne insert meters on a project. We were going to try them at locations of lower importance for reduced costs.

We ended up having to switch them out for Signet paddle wheel inserts. This was do to the fact that we installed cement lined ductile iron pipe where the meters were to be tapped. Upon startup, they did not read correctly so we contacted the manufacturer. Their tech support informed us that the sleeve where they were inserted needed to be unlined or stainless steel. Wish we would have known that prior to the piping installation; but, nothing was shown on their shop drawings, O&M manuals or cut sheets.

Krohne did however accept the returned meters for a full refund in this instance.

If you use them, contact the manufacturer to make sure the piping is correct.

 

[bioengr82]

All RO piping is stainless steel (316?).

 

[glennpan]

BioEngr,

It sounds like the problems the other people had with insertion mags were application based. If aplied well, they are a fine technology. Are they as good as a full bore magmeter? No. Are they an adequate low cost alternative to them for most applications? Yes.

As long as you know the limitations such as: 1. You need to have a full pipe. 2. You have to make sure that they are grounded. 3. They are more sensitive to coating, and changes in viscosity.

Signet makes a good product that we have used successfully on some of the systems that we build.

Glenn

 

[biglil]

I have worked w/ public agencies in SoCal that have successfully installed this electromagnetic flowmeter (insert- sleeve type) & telemetry equipment by this manufacturer: call their sales rep

http://www.marsh-mcbirney.com/Products/Multi-Mag.htm

 

[JimCasey]

The distinction I see is that an insertion unit only samples a point in the velocity distribution. A full-section magnetic flow tube (Magmeter) actually subjects the entire flow to as uniform a magnetic field as can be generated, and the induced voltage is indicative of the entire integrated flow through the magnetic field.

Magntic flow tubes therefore are forgiving of flow velocity distribution, short piping runs, and other effects that cause assymetrical flow profiles. An insertion meter will only be accurate if you are lucky to get it in the right spot, and it may not be accurate at different flowrates as the velocity profile shifts.

If there are coating problems, Magmeters are available with bullet-shaped electrodes, which may be heated and/or fitted with ultrasonic cleaners.

The magmeter must be kept full as noted in an earlier post. Keep the meter full by either installing it in a vertical line with upward flow, or in a horizontal line P-trap with an offset of anything greater than one [pipe diameter.

One thing that does drive magmeters nuts is if they are close to a chemical injection point and the chemical is still reacting as it passes thru the meter. Many reactions have an electrochemical component, and magmeters work on microvolts, so it is easy to swamp the signal with process noise.

Pulsed DC mags are also more noise immune than the old-style AC mags. The DC meters pulse the magnet coils, when the magnetic field stabilizes they take a voltage reading across the electrodes, then they shut down the coils and check the electrode voltage for a zero value. Then they pulse the magnets again with reversed polarity. Processing these signals lets them filter out biases and quadature errors. The DC pulse rate >can< be faster than line frquency, but it is never coincidental. Variations in local magnetic field (Heavy-current bus-Bar, large AC motor, etc. could cause the same quadrature effects as in the AC magmeter if the DC was pulsing at coincident frequency.