Vibration condition monitoring with Danfoss drives

Along with stator winding monitoring and load envelope, the CBM functionality integrated into the drive includes vibration monitoring. Vibration monitoring is realized with the help of vibration sensors, required for signal collection. The drive supports up to four vibration channels, connected to the analog inputs, 4-20 mA.

Vibration monitoring comprises 2 functions:

• General overall vibration level monitors mechanical vibration and is useful for early detection of main malfunctions such as imbalance, misalignment, mechanical looseness.
• The second function uses a different type of sensor calculated value, useful for monitoring bearing degradation, poor lubrication, and more.

The two functions are complementary to each other. The sensors provide a calculated output of a general vibration (v-rms) or bearing condition in wider frequency range (g-rms).

Vibration sensors from Hansford Sensors portfolio

Danfoss has entered a partnership with the global vibration leader, Hansford Sensors (HS). CBM vibration monitoring has been developed, tested, and validated using HS sensors. Hansford is a specialist in vibration theory, sensor selection and placement, and the partnership is mutually beneficial for both companies. Hansford manufactures high quality products with lifetime warranty.

Danfoss offers two types of sensors based on body shape:

1. Flat based: This body type is optimized for installation on prepared flat surface spots on the motor or machine, or to be used with mounting accessories. Mounting accessories are helpful when drilling/threading into the motor or machine is not an option. (Glue stud or magnet). Both accessories have a matching M8 female.
2. Conical: Easy to install on round surfaces, where we cannot obtain flat spot on the bearing housing. Very useful for smaller motors < 11kW. HS-D20C

There is a difference between optimal placement for v-rms and g-rms sensors.

Placement of the v-rms

HS-D20 used for monitoring imbalance, misalignment, and looseness is always on a rigid element of the motor housing. Ideally, position it on the drive end bearing or as close to this as possible. Some motors come prepared with a flat surface. The sensor can be mounted by drilling/threading or with a glue stud or even using a magnet if the surface is magnetic. There is less risk of signal loss for this type of RMS measurement.

Regarding axis, sensors can be mounted vertically or horizontally, as close as possible to the drive end bearing.

One sensor per motor is sufficient for motors rated up to 15 kW. For larger frame designations, we recommend multiple sensors, in a combination of types (v-rms and g-rms).

If only one sensor is installed, it is always good practice to measure both axes and select the one with higher level of vibration for permanent installation. The higher vibration is caused by structural resonance, stiffness, or freedom of movement, and it is important to determine the predominant direction.

The g-rms or bearing sensor

HS-D22 measures higher frequencies up to 5 kHz which do not transfer in the motor housing obviously. It measures the condition and lubrication of the bearing on which housing it is mounted. Therefore, mounting on the bearing housing is a must. Quality of the mounting is important for signal consistency. Achieve the best connection by drilling.

Electrical connection

For Danfoss drives, connect the sensors to terminal T12 (white) or terminal T13 for 24 V supply and AI53 (black) or AI54 for signal.