Belt Drive systems are a part of most industrial processes and can be critical to production. With the current signature capability of electric motor test equipment, belt drive problems can easily be identified. Belt drive systems exhibit similar indications for the following list of belt drive problems:

• Worn Belts
• Loose Belts
• Excessive Belt Tension
• Dished Belt
• Bad Belt Seam
• Mismatched Belts
• Eccentric Drive or Driven Sheave
• Misaligned Sheaves

Belt problems all share the same pulleys, pulley pitch diameter and belt length, so any problem with the drive system will result in a fault frequency related to those values.

Belt Frequency = (3.1416) (Pulley RPM) (Pulley Pitch Diameter)

                                                   Belt Length

RPM WILL ALWAYS BE LESS THAN EITHER PULLEY RPM

Normally generates 3-4 multiples of belt

Often the 2x belt frequency is dominant

Loose cog belt show at number of cogs times RPM

When belt frequencies are present, the best resolution is to check belt tension and alignment of the sheaves.  After alignment is completed and belt frequencies are still present, the problem is one of three things:

1. defective belt
2. eccentric driver sheave
3. eccentric driven sheave

                             Belt Frequencies on a 1200 RPM (20Hz) Motor

As part of a routine maintenance monitoring program, belt problems can be trended and identified as problems start developing. Use of infrared and vibration can also assist with the identification and correlation of data.