What to Consider on Establishing a Machine Health Control System

Output and Measurement Types

Generally, starting from no system there are several choices available. The easiest to implement is a 4-20mA system. It supplies proportional indication and trending of machine health without needing long term analysis. 4-20 mA outputs can be proportional to acceleration, velocity, or less commonly displacement. The general application is to establish Normal, Concern and Stop parameters within the machine operational limits. The 4-20 mA sensor provides continuous monitoring and in centralized control systems continuous indication of machine health. Decisions on maintenance can be forecast well before failure.

Overall Vibration Level

Since 4-20 mA sensors are designed for simple trending of overall vibration levels, it’s especially important to know the machine’s baseline so you can get meaningful results from the sensor signal. The baseline amplitude or “machine healthy state” is recommended to be 15-20% of the sensor’s range to allow for an original baseline and sensor range that will cover the changes in your machine health.

 Monitoring System

It sounds simple but if you are adding the 4-20mA monitoring system to current control systems make sure your monitoring system is equipped to handle a 4-20 mA signal. Don’t be stuck with great new sensors and no way to use them. Keep an eye out for HART-compatible systems, where a HART sensor can provide more features than just the 4-20 mA overall signal.

Environments and Requirements

Challenging operating environments–including temperature, moisture levels, possible contaminants, and nearby sources of interference–must be taken into account. Use the same considerations when selecting the cabling and mounting method as well.  If the installation point is in a classified hazardous location, be sure that the sensor and cable have the appropriate certification.

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