Smooth operators

Manufacturing downtime costs money. Whether it occurs in a small, discrete environment or a huge process plant, spending money fixing problems rather than making things to sell is bad for business. Do it too much and you could even see your company fall to more efficient operations.

No wonder then, that condition monitoring — the process of analysing physical changes in equipment to identify an increased probability of failure — is becoming more widespread.

By far the most popular method is analysing increased vibrations or irregular vibration patterns emanating from part of the equipment, using a vibration sensor or accelerometer, or an array of these devices.

This is particularly useful for checking bearings, where the analysis can be a key indicator of developing problems. Vibration and noise are produced by imperfections in the [ideally smooth] surfaces of roller bearings used in common engineering components such as gearboxes and other rotating plant, and increased noise and vibration are usually signs of impending failure. Failure can be caused by a number of factors such as bearing misalignment, bad lubrication, surface defects or poor fitting. It is preceded by vibration at a characteristic frequency which, if isolated from all the other sources of vibration in a working plant, can give a good indication of bearing condition.

installed a gearbox monitoring system to eliminate unscheduled shutdowns at Spenner Zement's Erwitte cement mills in Germany. And TEVA used

industrial accelerometers for vibration measurement at Kimberly Clark's Barrow paper mill, with 61 monitoring points for drives and gearboxes.

Sensors for condition monitoring need to be easily integrated into the system that most industrial buyers specify. Most manufacturers agree it is vital that sensors are inter-operable with various buses and wireless systems.

Products that claim ease of integration include

iT230 vibration transmitter and

Sensicast wireless condition monitoring solution.

Manufacturers also need condition monitoring applications to be rugged. UK vibration sensors supplier

stresses that its range of vibration, temperature and pressure sensors is suitable for the most demanding industrial environments.

aims its Model 1074 range of vibration transducers at heavy plant applications where reliability is essential. The 'efector octavis' from

is rated at IP69K and suitable for explosion-hazard areas.

Land-based manufacturers are not the only ones to use condition monitoring. Bearings are an integral part of the propulsion system for delivering power to engines on ships and a huge amount of effort is expended in ensuring they do not fail and limit the ship's manoeuvrability.

A system installed on the

cruise ship by

also relays information on vibration, temperature and oil quality to both on-board and land-based monitoring stations via a satellite link. The SKF MasCon48 condition monitoring system collects data from sensors on the ship's pod-mounted propulsion systems.

Sensors continually monitor the level and pattern of vibrations emanating from the shafts and bearings on each of the pods. Temperature sensors also monitor the motor windings and bearings. More sensors, and particle counters mounted in the oil sumps, keep track of the quality of the lubricating oils. Data anomalies are relayed to the crew, SKF and Rolls-Royce, the engine manufacturer.

Monitoring of shipping parts is big business and manufacturers are taking notice. For example, Amot's XTS-W system for monitoring bearings has received Lloyd's Register Type Approval. The company aims to provide monitoring of bearings on slow-speed propulsion engines for real-time protection of all crank bearings.

Another sensor aimed for use at sea is

ViSmart Viscosity Sensor, which the Canadian Department of National Defence (DND) is considering for real-time lubricant monitoring of ships. The sensor is a solid state semiconductor device with no moving parts and, once sealed, is claimed not to need field calibration.

The DND intends using data captured by the sensor as part of a programme to optimise engine performance and maintenance. Changes in viscosity have been tracked as a function of temperature, which monitors fuel dilution effects on the condition of the lubricant oil.

Some interesting developments in the naval arena are being made by US-based

, which is making wireless strain sensors to monitor operational loads on rotating components of US Navy helicopters. From the load data (transmitted wirelessly) the helicopter's system can model the degree of metal fatigue and calculate the estimated remaining time to failure of various helicopter parts.

The sensors are also designed to be self-powering by converting cyclic strains into DC power using piezoelectric materials. They are able to perform even under straight level flight with low cyclic strain levels and correspondingly low energy generation. With a wireless range of some 70m the sensors only require 0.9MW to operate.

Energy harvesting of this kind has also been in the UK news lately as

has developed a battery-free truly wireless condition monitoring sensor. The Perpetuum Microgenerator powers a vibration measurement system made by Pruftechnik. The generator — with vibration sensors and 802.15.4a wireless transmitter — constitutes the first commercially available self-powered sensor unit using piezo-electric energy harvesting.