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Ultra sonic flow meters Answered

We have 4 independent ultra sonic flow meters and they give us ghost readings at random times. We are sure it’s not emi from an outside source. It’s a frequency signal that our flow computer picks up without product ever running through the pipe system. It only happened at random times like 3 or 4 weeks apart. And are happening more often. Does anyone know best way to troubleshoot.


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2 years ago

Depending on the enviroment and cable length interference can be an issue.Especially if the signal lines are close to other cables.
Anything mains voltage or that has a modulated signal can cause your problems.
We had it with other sensors and replaced whatever we could think off to no avail.
Then one day a guy started swearing a bit too loud when the sensors failed and ruined the workpiece.
After a few rounds of that another guy made the missing connection.
For us the cause was an ultrasonic plastic welder, or to be precise it's electromagnetic holding clamps.
The reverse protection diodes had failed and every time the clamps operated (or almost every time) the also missing earth connection on the fancy power supply caused a bad feedback in our mains lines.

In the end we both fixed the diodes and power supply as well as adding additional filters for high EMF producing equippment.
As a quick check you can try to add ferrite tubes over the signal cables, preferably with a loop of the wire going through instead of just a straight, single line.
If that helps then you have EMF problems somewhere, maybe a loose contact or so.
If it does not help at all then I suspect an intermittent failure of the computer.
Double check that the power supply has a proper earth connection and that ALL connected equippment is grounded as well.
For example modern switch mode power supplies can be a real pain in the behind.
Connecting my external hard drive to power causes the monitor to make a single flash as its power supply is of the same kind and same outlet.
Similar story for a lot of USB hubs.
They fail to seperate the ground connections or at least have them filtered, instead it is a direct connection between ports, power supply, computer and connected things.