Sensors and Transmitters For Industrial Compressed Air Systems

Improve compressor efficiency and reduce energy cost

For many years, the maintenance of industrial equipment has been time-based or, in some cases, simply to allow equipment to run until failure. More recently, with the advent of increasingly sophisticated monitoring and data gathering technologies, we’ve seen a gradual shift from reactive to predictive, or condition-based, maintenance programmes.

This change has been – and continues to be – driven by the need for industry to become ever more efficient. This is especially true when margins are under pressure. It has also been driven by the introduction of increasingly tough safety legislation and, most recently, by concerns about climate change and energy saving.

Although predictive maintenance technologies were first used with high value or critical production systems, they are now being applied as standard to a growing number of lower-level devices, ranging from pumps, fans and motors to compressors and dryers.

According to a recent report by Research And Markets, the global market for predictive maintenance products (hardware and software) is forecast to grow by a CAGR of 31% until at least 2030. Clearly, there is still a long way to go before the practice has been adopted throughout industry.

Industrial compressed air

In many respects, industrial compressed air systems represent a microcosm of this shift. The traditional approach was to install them at the back of a factory or some other out-of-the-way location, where they were generally only remembered when something went wrong.

Today, most industrial compressors are situated in dedicated compressor rooms and feature intelligent monitoring and real-time control devices, linked to advanced sensors that measure every aspect of operation. These enable compressors to be run efficiently, to minimise energy consumption and ensure consistent air quality. They also allow maintenance to be planned in advance, at a time when production demand is low, and can help both to extend the operating life of compressor components and the intervals between servicing.

As a minimum, these sensors normally include pressure and temperature fitted on the air inlet side of the compressor, plus vibration to indicate wear on rotating parts, while on the outlet (downstream of the dryer) there will be a flow meter and, perhaps most importantly, a dew-point sensor. Further sensors may also be fitted elsewhere in the system; for example, pressure and flow sensors can be used in distribution pipework to measure fluctuations in the pressure being delivered to tools or equipment powered by compressed air.

Dew-point is key to energy efficiency

Almost all processes and systems that require compressed air are at risk of damage from moisture. This naturally occurs in the atmospheric air drawn into a compressor. Moisture can cause multiple problems: corrosion, damage to seals, emulsification of oils and, if air is used as part of the product manufacturing process, such as in food and beverage production, poor product quality and the risk of bacterial growth.

Water in atmospheric air normally occurs as vapour. However, air can only absorb so much vapour before it condenses as a liquid. For example, air at 20°C can absorb up to 17.3 g/m³ of vapour before becoming saturated; beyond this point – known as the dew point – a phase change occurs as vapour condenses into a liquid; in nature, this is commonly as dew, rain or frost. A similar situation will occur within compressed air systems as hot air from the compressor cools on its journey through downstream devices.

A dew-point sensor allows the moisture content of the compressed air to be accurately measured. In particular, by using a dew-point sensor on the dryer outlet, with a feedback loop to the dryer control unit, it becomes possible to manage the desiccant drying columns within exact parameters, thereby ensuring maximum efficiency. A dew-point sensor also allows the volume of purge-air and the frequency of purging to be minimised; in regenerative twin-column desiccant dryers, for example, a dew-point sensor will switch from the active column only when its performance falls below a predetermined level.

Using a dew-point sensor, in conjunction with other control devices, is therefore key to an effective maintenance strategy. In addition, it will reduce energy consumption, extend the operating life of dryer components and desiccant materials, and ensure optimum product quality in applications where the compressed air stream comes into contact with the finished product.

Dew-point sensors or Transmitters

The latest generation of dew-point sensors or transmitters, such as our Easidew range, use the Michell ceramic metal-oxide technology to provide exceptional levels of accuracy, hysteresis and reliability. Each sensor is manufactured using thin- and thick-film deposition techniques, with a hygroscopic monolayer sandwiched between two charged layers of conductive material. The monolayer adsorbs water molecules. These have dielectric properties, which alter the capacitance between the metal layers; this is proportional to the level of moisture present, enabling precise measurements to be taken, even at trace levels.

The technology is tried and tested, with modern sensors being exceptionally robust, making them ideal for use in all types of compressed air application.

Learn more about our latest Michell Easidew sensors or transmitters

With over 45 years of experience in trace moisture measurement, we are the application experts when it comes to controlling moisture in compressed air. Contact us to discuss your application.