Step chains and steps are the components that undergo significant degradation (wear) during the operation of an escalator. Therefore, they need to be replaced several times within the service life of the machine. Currently, the criteria adopted to determine the condition of the chain is based on the step to step gap which is measured during the inspection of the machines. It is normally accepted that when gaps between steps are bigger than 6 - 7 mm, the step chain should be replaced. A good number of the step chains in operation do not give the estimated service life. There have been instances where step chains were in service for approximately 5 years and this has huge financial implications more so in this current economic climate. There is limited understanding of the impact of the loading conditions, maintenance regime, cleaning of chains etc have on chain life. To overcome some of these problems and in keeping with London Underground's predictive approach to maintenance, it was decided that a system for monitoring the step chains should be developed which will enable significant improvement in the reliability of the machine and consequently will result in a reduction in the maintenance cost associated with replacement of steps chains. The system developed measures the chain stretch and the displacement of the lower tension carriage and plots the processed data as time plots.
