To obtain information like this, a sensor that provides an output proportional to the actual level in the vessel is needed. Often, this can be arranged very simply by using a pressure sensor installed at the base of the vessel, which, in effect, provides a continuous readout of the vessel’ s weight plus its contents.
Sometimes, however, a more sophisticated solution, such as a radar level sensor, may be needed. Radar sensors can measure liquid levels with millimetre accuracy at a range of up to 10 metres from the surface of the liquid. This makes them ideal for hygienic applications as they never come into contact with the liquid they are monitoring. Another benefit is that they are typically installed above the vessel rather than at its base, and so are usually very easy to retrofit.
Moving on to temperature, it’ s not hard to see that accurate temperature control, especially when temperatures significantly above or below ambient are involved, is important for maximising energy efficiency. Accurate temperature control can also lead to improved product quality and reduced wastage. Fortunately, modern temperature sensors are capable of very high accuracy and are available in a wide range of types and sizes. This means it’ s often worth reviewing existing temperature control systems to see whether energy-saving improvements can be made at no more cost than fitting a replacement sensor.
Pressure is another process variable that’ s worthy of attention. Pressurising vessels and plant – or generating vacuum – uses energy so, as with temperature, accurate control is crucial for energy efficiency. However, with pressure, there is another aspect: a slow loss of pressure may indicate a leak that would otherwise be hard to spot. The substance leaking may be valuable, dangerous to people and the environment or even valuable and dangerous. Therefore, a new or additional pressure sensor could quickly repay its small cost by revealing such a problem.
So much for directly monitoring process variables, but what about monitoring machines? Here, one type of sensor that isn’ t as widely used as it deserves is the vibration monitor. This can be a valuable addition to almost any type of motor driven plant or machine and is usually easy to retrofit. The sensor will allow any anomalous increase in vibration to be swiftly detected, and this will almost always suggest that problems are developing. If increased vibration is, for example, a sign that a bearing is starting to fail, the machine will be using – and wasting – more energy than usual. It will probably also be heading for a complete breakdown with loss of production and, in many cases, scrapped products and wasted raw materials.
With scrapped products in mind, let’ s move on to quality control. Most production lines incorporate some form of quality control, but the degree of sophistication varies greatly. The‘ gold standard’ for automated quality control is often a sophisticated vision system and associated computing power, but these systems can undeniably be costly. Fortunately, there are now simpler, more affordable systems
AUTOMATION, CONTROL & ENGINEERING 21