hi,

i am wondering what types of interference could be causing a flowline ultrasonic sensor from long having periods of working perfectly to sending back full tank or empty tank readings for 10 secs to 5 hours. this has been going on for months. i am thinking of possibly ham or cb radios, due to them operating at 50 mghz. any thoughts would be greatly appreciated.

rick

 

could you be interference, could be misapplication...if you are sure that it is a good application (no problems with physical installation, sure that it is not a one off transmitter "glitch") then I would look at PLC panel and look for improper grounding of signals and equipment. That can be a difficult job in a running facility, but nevertheless, depending on context of problem, you have to look.

My favorite is a VFD drive in the area that is grounded on the instrument ground, that can cause some problems with analog signals.

I have not seen Ham radio causing problems, I would think you would have to be very close to a powerful transmitter before that might be a problem. YMMV

 

It would be very difficult to tell. My guess is that there is some other cause of signal lock loss than that.

What I would suggest, though, as a workaround is that you set alarm trips on the signal output at 4.0 mA and at 20.0 mA. When those alarms trip, have them shut off a relay in the power line to the sensor or transmitter, or both. Make it a time-delay-relay about 30 seconds. This should recycle the level transmitter and should provide lock on to the accurate level. Of course you should go look the first few times. If you can, log the activity and see if you can correlate it with something else going on at the same time.

Good luck,

Walt Boyes
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Control and ControlGlobal.com
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