Understanding the Vibrometer

1. Definition: What is a Vibrometer?

A Vibrometer, often called a vibration meter or a vibration pen, is a simple, handheld electronic instrument used to perform quick checks of the overall vibration level on a piece of machinery. It is a screening tool designed for ease of use by maintenance staff, technicians, and operators, and it does not require deep expertise in vibration analysis.

Unlike a sophisticated vibration analyzer, a vibrometer does not typically display a frequency spectrum. Instead, it provides a single number that represents the total amount of vibrational energy within a predefined frequency range.

2. How a Vibrometer Works

A vibrometer integrates a sensor (usually an accelerometer), signal processing electronics, and a display into a single, compact unit:

1. The operator presses the tip of the vibrometer against a bearing housing or other machine measurement point.
2. The internal accelerometer senses the vibration and converts it into an electrical signal.
3. The internal electronics filter the signal to a specific frequency range (e.g., 10 Hz to 1,000 Hz, as recommended by ISO standards for general machine health).
4. The filtered signal is processed to calculate an overall amplitude, most commonly the RMS (Root Mean Square) of velocity.
5. This single RMS velocity value is shown on the display (e.g., 4.5 mm/s).

Many vibrometers use a simple color-coded display (Green, Yellow, Red) based on the vibration severity charts in standards like ISO 10816 to provide an instant “Good,” “Satisfactory,” or “Unacceptable” assessment of the machine’s condition.

3. Role in a Maintenance Program

Vibrometers are an excellent entry-level tool for companies starting a condition monitoring program. They bridge the gap between doing nothing and implementing a full-scale predictive maintenance program.

• Screening Tool: They are used to quickly screen dozens of machines. If a machine shows a high or increasing vibration level on the vibrometer, it can be flagged for a more detailed investigation by a trained analyst using a proper vibration analyzer.

– Operator Rounds: Operators can be trained to use vibrometers as part of their daily or weekly rounds, providing an early warning of developing problems.

• Verification: They can be used to verify the success of a repair. For example, a reading can be taken before and after a bearing change or alignment job to confirm that the vibration levels have been reduced.

4. Vibrometer vs. Vibration Analyzer

Vibrometer (Vibration Meter)

• Purpose: Quick screening and overall level checks.
• Output: A single overall vibration value (e.g., RMS velocity).
• User: Maintenance technicians, operators, mechanics.
• Function: Answers “Is there a problem?”

Vibration Analyzer

• Purpose: In-depth diagnostics and root cause analysis.
• Output: Detailed FFT spectra, time waveforms, phase readings, etc.
• User: Trained vibration analysts.
• Function: Answers “What is the specific problem and how severe is it?”

While a vibrometer is a valuable tool for its simplicity and speed, it cannot diagnose the specific cause of the vibration. A high reading indicates a problem exists, but it takes an analyzer to determine if that problem is unbalance, misalignment, a bearing fault, or something else.

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