4-20 mA vibration sensor
4-20 mA vibration sensors provide simple and reliable monitoring of machine vibrations. The sensor integrates directly into PLC or SCADA and makes it possible to detect changes in vibration levels before they develop into downtime.
4-20 mA vibration sensors
Simple and reliable machine vibration monitoring
4-20 mA vibration sensors are used for continuous monitoring of vibrations on rotating machinery such as motors, pumps, fans and gears.
The sensor measures vibrations and converts the signal to an analogue 4-20 mA output that can be connected directly to PLC, SCADA or other monitoring systems. This way, the machine's vibration level can be monitored online and alarms can be set up if the vibrations exceed a set limit.
Typically applies:
- 4 mA = no or very low vibration
- 20 mA = maximum vibration level
The PLC or monitoring system can then convert the signal to For example mm/s or g so that the vibration level can be monitored and used for alarms or trend analysis.
How does a 4-20 mA vibration sensor work?
A 4-20 mA vibration sensor is usually based on an accelerometer that detects vibrations on the machine.
The process typically works like this:
- The sensor detects vibrations as acceleration (g).
- The signal is integrated into vibration velocity (mm/s), which is the most commonly used parameter for machine monitoring.
- The signal is filtered over a specific frequency range so that only relevant vibrations are included in the measurement.
- The vibration level is typically calculated as an RMS value.
- This value is converted to a proportional current output between 4 and 20 mA.
The PLC or monitoring system can then use the signal for trend monitoring, alarms and machine protection.
What can a 4-20 mA vibration sensor tell us?
A 4-20 mA vibration sensor measures the overall vibration level of a machine.
The sensor can therefore:
- Detect changes in vibration level
- Alarm in case of elevated vibrations
- Indicate that a machine starts to behave differently
However, the sensor usually cannot identify the exact type of fault.
If the vibration level increases, it could be due to, for example:
- Imbalance
- Rental damage
- Mechanical looseness
- Misalignment
- Gear problems
- Cavitation in pumps
- Resonance in the construction
The sensor tells you that something is wrong, but not necessarily what is wrong.
If elevated vibrations occur, a detailed vibration analysis with accelerometer and FFT can be used to identify the specific fault.
4-20 mA vibration sensor vs. accelerometer for vibration analysis
There are two main types of vibration sensors for condition monitoring.
Sensor type:
Application:
4-20 mA vibration sensor
Online monitoring and alarm
AC accelerometer (mV/g)
Fault diagnosis and vibration analysis
4-20 mA sensors are therefore typically used for machine protection and monitoring, while accelerometers used for detailed failure analysis.
Vibration protection with trip module
A 4-20 mA vibration sensor can also be used for machine protection.
By combining the sensor with a trip or monitoring module, the vibration level can be used to trigger an alarm or stop the machine automatically.
A typical solution consists of:
- 4-20 mA vibration sensor mounted on the machine
- Trip or vibration monitor
- Alarm or shutdown signal to PLC or control system
If the vibration level exceeds the set limit value knows the system:
- Activate alarm
- Send signal to PLC
- Stop the machine automatically
This type of solution is often used to protect pumps, fans, motors and gears where elevated vibrations can lead to serious damage.
Standalone vibration protection
In some installations, a simple and standalone vibration protection is desired, without integration to PLC.
Here, a vibration sensor can be combined with a vibration trip sensor, where the alarm and relay function is built into the device itself.
One example is the Hansford HS-429 vibration trip:
- Monitors the vibration level directly on the machine
- Has built-in alarm and trip function
- Can activate relay when limit value is exceeded
- Provides simple and robust protection for machines
This type of solution is often used on:
- Pumps
- Fans and blowers
- Compressors
- Smaller machines
- Systems without PLC system
Advantages
-
Easy integration
Can be connected directly to PLC and existing monitoring systems. -
Continuous monitoring
Machines are monitored online without manual vibration measurement. -
Alarm and protection
Possibility of alarm or shutdown in case of elevated vibrations. -
Robust signal
The 4-20 mA signal is stable over long cables and in industrial environments. -
Cost-effective solution
Suitable for monitoring many machines in a plant.
