Help me find a suitable speed sensor


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I need to install a speed sensor in a roll in tandem cold mill and with 4 to 20 mA output to connect with PLC. The roll surrounding is full of water and lubricant.

If anybody knows any non-contact speed sensor with 4 to 20 MA output which can work in surrounding water and lubricant environment, please tell me. I need it urgent basis.

Thank you for your help.
I’m no expert here but the first question I would ask is – is there any exposed shaft visible or accessible? I’d be thinking about using a proximity sensor to generate a frequency proportional to the speed of shaft rotation, and feed this into a frequency to analog converter to get an isolated analog input if that’s what you want for the PLC.
For mining applications measuring the high speed spokes in large pulleys I used to specify a Milltronics MFA 4P this is now under the Siemens brand The sensor has a 4" measuring range. I'm mot sure if they have a 4 - 20 mA option but it may do what you need.

If the speed is low you can use a proximity switch detecting a target on the roller shaft letting the PLC calculate the speed.
Two timers set to monitor the On/Off state of the proximity switch can be used as a low speed alarm.