hello I am looking for some free information. I have a Fischer Porter Mag meter. I have recently had a erroneous flow meter reading what seems to be caused by a reverse flow through the unit. the reverse flow was caused by a valve failure. I was of the understanding that mag meters only metered flow in one direction, the direction stamped on the meter body? Am I wrong? I would appreciate any input.
Thanks in advance

 

Yes, you were incorrect. The magnetic field doesn't care what direction the moving conductor is moving in. Unless the converter and transmitter have direction indication circuitry built in, the meter will measure quite well in either direction. The meter was working right.

Best,

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
[email protected]
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------

 

Jim:

While mag meters are referenced with an arrow or other marking for flow direction, most current technology will allow reading flow in either the
positive or negative direction. This feature can usually be turned on or off via the transmitter programming. Some manufactures will also allow you to set positive, negative or net totalizer functions also. Check the manual for your partiular model and select those features you want to use.

Regards,

Wayne Shimanis

 

Responding to Walt Boyes reply:

Are you sure that conductor alignment relative to magnetic lines of force is not crucial. I thought the induced current was related to the "Dot" product of the two vectors, AxBxCos(phi)! If vectors are parallel,the product is zero.

Regards,
Phil Corso, PE
(Boca Raton, FL)

 

I think I'm guilty of sloppy language. We are talking about a fluid constrained in a pipe, here, so the directions in question are "forwards" at right angles to the electrode plane and "backwards" at right angles to the
electrode plane. In that sense, the field doesn't care whether the fluid is moving "forwards" or "backwards," it will still generate a voltage on the electrodes proportional to the speed of the moving conductive fluid in the pipe, regardless of direction.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
[email protected]
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:1-253-981-0285
--------------------------------------------

 

Walt,

If the flow is reversed, won't the polarity of the developed EMF reverse with it?

This obviously will have some effect on the system, but what that is will obviously depend on the electronics. It does make a difference in at least one that I have played with.

Bruce.

 

Yes it can, Bruce.

Where this normally makes a difference is in a gravity flow wastewater line in a u-bend, designed to keep the meter full, and there is a surcharge condition beyond the meter. Flow then moves up the line, through the meter body, and the meter totalizes flow...even though it is in reverse.

Most magmeter manufacturers have an option to bring out the reverse flow, stop the forward flow output and totalizer. This is useful, not only in wastewater, but common in HVAC and building automation systems also.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel" www.spitzerandboyes.com
walt(AT)waltboyes.com
21118 SE 278th Place
Maple Valley, WA 98038 253-709-5046 cell
425-432-8262 home office
fax:1-253-981-0285
--------------------------------------------

 

Fischer Porter Mag meter records flow in both direction i.e. forward & reverse. if the pump at the input of the flow tube is stop & there is liquid in the pipe & also if the valve at the outlet of the tube is closed, then reverse flow can occur & the Fischer Porter mag meter will calculate it.