Magnetic Pickup Sensor Waukesha Gas Engine


Thread Starter



I need help in replacing a speed sensor installed on Waukesha gas engine 12V275GL by another type, as the installed one is not working in a smooth manner and stops the engine on "too many magnetic pulses alarm". the question is how to choose the correct magnetic pickup type for this application!

The installed magnetic pickup Model is: 640B01
Platinum 4-20 mA Output Velocity Sensor, manufactured by IMI sensors.

Note: this problem is happening in 3 identical Waukesha gas engines.


A velocity sensor is not a speed sensor; it's a vibration sensor, sometimes called a "seismic" vibration sensor. It measures the magnitude of velocity associated with vibration (the sudden changes in motion associated with vibration).

How long has this problem been existing? Since commissioning? Since some recent refurbishment work? In other words, if the problems have not existed since commissioning but have started more recently, what has changed? Has wiring been replaced? Have the sensors been removed and replaced during some mechanical maintenance outage? Have the sensors been replaced with new sensors (possibly ones that don't meet all the requirements of the application, but are less expensive than ones that DO meet all the requirements of the application)? Trying to understand what happened prior to this problem coming up can help with the troubleshooting.

How old are the sensors?

Are you certain the sensors are securely and properly mounted where they should be?

What is the conditions of the wiring between the sensors and the control system the sensors are connected to? I would presume that twisted, shielded pair wiring with a shield drain wire which should be terminated at one end only; a LOT of nuisance problems incorrectly attributed to sensors or control systems is the result of incorrectly wired low-level analog devices (and this 4-20 mA sensor falls into that category of device).

Is the sensor rated for the temperature of the location(s) where they are installed?

What does the engine packager/manufacturer say about the problem?

There are vibration simulators which can be used to test the sensors to see if they are accurately calibrated or are out of spec's (sometimes these testers/simulators are called "shaker tables"). They can be rented from some instrument calibration rental companies, and would require temporarily removing them to mount them on the tester/simulator. If there's any question about the wiring between the sensor and the control system, it's a good idea to take the tester/simulator out to the location where the sensors is located and leave it connected to the control system with the existing wiring and test it that way.

Again, a LOT of times problems like this can be traced to wiring issues, as simple as checking and making sure that shield drain wires are terminated at one end only.

Hope this helps! Please write back to let us know what you find.
Thank you CSA for your response,

this problem was happening since the commissioning of the 3 units. anyway I will check all the conditions you stated in your response and I will come back to you with the full picture.