rosemount 8712 flow meter coil open circuit

The rosemount 8712 flow meter is displaying coi open circuit. Should iI just replace the sensor? I looked in the troubleshooting and only thing im seeing is if the resistance between the coil is a certain oms it means an open or bad coil and the sensor should be replaced. just looking for ideas before i climb down a 30 foot ladder into the sewer.

I hope you're taking a gas detector and are harnessed with a retrieval system, rescue plan, safety observer and the required training... because that sounds like a confined space entry to me.

Before doing all that, I'd disconnect the sensor wiring at the transmitter end and test it using an ohmmeter. Is the coil actually open circuit?

Flowmeter sensor elements are very reliable (basically just a coil of wire). It's more likely to be a damaged cable or some other issue.

That's assuming it was correctly potted at the sensor end.

Saffa said:

I hope you're taking a gas detector and are harnessed with a retrieval system, rescue plan, safety observer and the required training... because that sounds like a confined space entry to me.

Before doing all that, I'd disconnect the sensor wiring at the transmitter end and test it using an ohmmeter. Is the coil actually open circuit?

Flowmeter sensor elements are very reliable (basically just a coil of wire). It's more likely to be a damaged cable or some other issue.

That's assuming it was correctly potted at the sensor end.

Click to expand...

yes, doing all the required confined space requirements, so to disconnect the wiring at the transmitter end means up on top? or is that at the actual meter?

The electronics box is called a converter or a transmitter and can be mounted directly on the flow tube or remotely.

If mounted remotely, presumably above grade, where you have easy access, then you want to disconnect the cable from the flow tube at the transmitter end and check the coil resistance with an ohm meter at the transmitter end.

A loose connection can appear as an open circuit so pay attention to how well the cable is connected when you disconnect at the terminal block.

A cut or smashed cable could appear as an open circuit.

The coil wires frequently are in terminal box on the flow tube and it could be a loose or damaged connection at that point, as well.

fgoodsky said:

yes, doing all the required confined space requirements, so to disconnect the wiring at the transmitter end means up on top? or is that at the actual meter?

Click to expand...

As DanW elaborated on - yes as the top.

DanW's possible causes are also spot on.

When I've had similar issues it has always been a damaged cable, corroded terminal or loose connection in either the transmitter or the sensor terminal box

We have many of these type of meters all with remote LOIs. What we find, even with the new style potted heads, is the coils in the tube fail. Meaning tube replacement. If your ohm reading show an open coil, you can check the wiring terminals. Be prepared to take the same readings with the cables disconnected. We have one now that works fine until it gets cold, then the LOI shows an open circuit. That unit will be replaced next week.


All of ours are above ground. We replaced our last underground meter years ago. Too many issues with access.

That's interesting that you have had multiple failures Sleddog. What sort of environmental conditions are these meters used in?

We look after hundreds of old ABB Magmasters, newer Watermasters and Endress Promags of various models. Don't think I've ever had a bad coil. The Watermasters were terrible compared to the original Magmasters, but that was due to transmitter design i think.

Our failures have always been due to damaged cable or failure to pot the transmitter terminal box after wiring and then having moisture ingress