Wastewater magmeter versus ultrasonic meter ?


Thread Starter


I recently read a thread concerning ultrasonic versus magmeter for a landscape irrigation application. I am concerned with a different application; therefore, a new thread appears warranted.

I currently have an existing 12-inch diameter electromagnetic flowmeter installed in line with a 16-inch sanitary sewage forcemain used for customer billing purposes. Ferrous chloride and hypochlorite are injected a distance upstream into the collection system for odor control. It appears the chemical addition, and perhaps additional constituents in the waste stream, contribute to a coating buildup within the magmeter flow tube. I am unsure if both the flow tube and the electrodes are fouled. The meter results are unreliable and drop consistently over time, well out of the expected range. Existing velocities are most likely between 2.5 feet per second and 5.0 feet per second, most likely lower than recommended to prevent coating the magmeter. Downsizing the meter to increase velocity may not be completely viable.

Others have recommended an inline ultrasonic transit-time flowmeter for this specific application. Are there significant drawbacks or fatal flaws in using this meter for this application?

What about ultrasonic doppler versus ultrasonic transit time for use in this application?

Any user experience with this particular scenario?
Any user experience with self-cleaning magmeter electrodes and/or removable magmeter electrodes?

Thank you for any assistance.
Hi there,

The mag flow is the correct meter for your application, stay with it.

What you can do to improve reliability and accuracy is to implement a two yearly full inspection, cleaning and calibration verification service contract with the supplier of the mag flow or some other instrumentation field services company. That is if you are unsure how to maintain and calibrate these magflows yourself.

If you have the correct inner lining for your application and the self cleaning bullet shape electrodes in, there is no reason to go for anything else. With a bit of maintenance and verification checks it should give you perfectly accurate readings. The product you use will be highly conductive and magflows like that, so stay with it.

Here is something you can read on magflows that are used in similar applications,

A good self cleaning Magmeter with bullet nosed electrodes will help but if you are having a high frequency of maintenance to keep the tube clean due to low velocities, there is one product which is a Sonar array-based flow instrument that I have used and it works in a high scaling service in an alumina refinery. Attention must however be paid to low cut-off on these instruments.

Rohit Chandak

No doubt Mag Meter is the best choice for the application. the one thing that I would like to know is whether the meter was performing well within your satisfaction level initially & developed the problem lately. Transit Time will never work correctly on this application, if you want to try you can use Doppler Ultrasonic Flow Meter but lining build up could lead to errors in measurement. Nothing hard to try since if that works that would be the most appropriate meter for the application without much of maintainance requirement but definitely much inaccurate than Mag Meter.
Sam, Jonas, Robert, and Rohit, thank you all very much for your advice.

Rohit, to answer your question, the meter never performed well on a consistent basis. For an initial period of about 6 months, the meter was somewhat consistent. However, after approximately 8 months of service, the average daily flow readings slowly decreased. The flow readings then sharply increased and the pattern repeated itself about three times so far. Seemingly indicative of a gradual buildup of a conductive (or non-conductive?) coating causing loss of flow signal. Thank you.

Rohit Chandak

Thanks, that is definitely loss of signal due to build up or large presence of bubbles/dirt in the process line. Either you should use Doppler Ultrasonic or best way use a Hybrid Ultrasonic Flow MEter which switches itself from transit time to doppler based on the service. I would recommend Controltron, Inc. USA's (now Siemens)Clamp On Ultrasonic meter which matches the sonic velocity of the pipe (including buildup) to give best possible signal strength for the application. It does also work from Transit Time to Doppler or vice versa. I would advice you to take a trail unit or ask manufacturer to test the application using portable device & than procure the same if the results are satisfactory.
Rohit, thank you again. I am of the opinion that an inline ultrasonic is superior to a clamp-on ultrasonic. Are you in agreement?
forget about any type of ultrasonic flowmeter for sewage!

Stick to mag flow. There are self calibrating meters which in reality do not do the calibration but they can do a self check.

E+H has good meters for sewage with reasonable price. I personally used more than 70 of them in a single sewage treatment plant project. Very satisfied.

Good luck,
also try to check the Mccrometer Propeller type flow meter, I've installed a couple of these in wastewater system. But if your medium contains large amounts of slurries and particles I suggest you stick with the electromag.
Hi again,

I agree with Hamid.
Also stay away from the portable Doppler ultrasonic test meter it's junk, and totally unreliable.
we used KROHNE mag flow meter which is having self diagnostic feature to know the coating in the electrodes..
hi all,
I am looking for waste water meter (mechanical display): low cost, good quality... at Euro, middle east...pls help me.
If you are working with #2 or better effluent (suspended solids less than 20 mg/l) you can use a propeller or a turbine meter. They are mechanical meters and often are supplied with mechanical registers. One vendor I think highly of is McCrometer div. of Hach Danaher. There are others.

If you are working with wastewater containing high amounts of suspended solids (greater than 20 mg/l) you almost are forced to use a spool piece type magnetic flowmeter. They do not come with mechanical registers, but there are several low power magnetic flow meters available now that are two-wire or even a couple of battery operated versions. I like the Yamatake (asbil) two wire magnetic flowmeter quite a bit. There are others.

The reason you are forced to use a magnetic flowmeter is the fact that magmeters handle very large solids loads, large solids mesh sizes, and to a great extent, can handle oil and grease coatings.

You can use an ultrasonic (transit time) flowmeter for the effluents I talked about earlier, but they require power.

Vendors will tell you that you can use clamp-on ultrasonic doppler flow meters for wastewater. While I agree that you _can_, having worked with doppler flow meters for many years, I wouldn't use one when a magnetic flowmeter would be available and usable.

I hope that helps.


Walt Boyes
Editor in Chief
Control and ControlGlobal.com
555 W. Pierce Rd Suite 301
Itasca, IL 60143

[email protected]
We are rehabilitating a wastewater lift station. The engineering firm specified a 16" magmeter. Right now I have at least three failed Sparling magmeters at other lift stations, so needless to say, I'm not thrilled with another one. I realize that there are good mag meters that will work fine in this application. This new one wouldn't be a Sparling. But mag meters are expensive and we are always looking to save money where it won't hinder operation. If this mag meter fails at any time, then we get into the huge task of removing and replacing such a large meter. You see where I am going with this. Earlier in the thread, someone mentioned a Siemens strap on meter that switches from transit time to Doppler based on the service. Does anyone have any thoughts on this or other strap on meters for use at lift stations?

Thank you.
what type of electrode cleaning do you use for in service cleaning?

> We are rehabilitating a wastewater lift station. The engineering firm specified
> a 16" magmeter. Right now I have at least three failed Sparling magmeters at
>other lift stations, so needless to say, I'm not thrilled with another one.

---- rest of included quote cut ----
The coils have failed on the spool (Pipe) pieces. Which means the whole pipe piece has to be removed and either repaired at the factory or replaced with new.

Regarding electrode cleaning. The electrodes aren't removable. Nor can I access the pipe to clean them.

"what type of electrode cleaning do you use for in service cleaning?"

Richard Lowrie

A well built magnetic flow meter should never have coils fail after such a short time in service. Are the coils getting wet? (tube leakage?) If so an IP68 rating on the tube should resolve this problem.

As far as cleaning electrodes some manufacturers have removable (hot tap) options for this purpose. to me it sounds like the meter is getting submerged and that is the reason for the failure.
I agree about the submergence. The other thing that will kill coils like this is dirty power. High frequency transients will fairly rapidly degrade coils and cause failure.

Walt Boyes
Spitzer and Boyes LLC
3433 Connecticut St
St Louis MO 63118
[email protected]
office: +1-630-639-7090