Integrated Electrical Transducers for Condition Monitoring Allow
Improved Safety, Quality, Efficiency and Profitability

Bertrand Klaiber, Marketing Manager
LEM SA

Industrial processes make use of many different kinds of sensors to register miscellaneous parameters and execute the necessary control commands at the correct time. Facility supervision and equipment management also require advanced monitoring to ensure safe operations, efficiency and reactivity of automated processes, to identify sources of savings, schedule maintenance operations and anticipate and prevent failures. Traditional condition monitoring still implies regulation parameters such as temperature, pressure, torque, position and others, but measuring these directly can be both inefficient and inaccurate. Measuring the input current of a load provides more information than just the current value and has a number of advantages:
• Speed: Load changes are detected immediately, which can prevent equipment failure and avert process disruption.
• Ease of Use: A contactless current transducer or switch can simply be snapped over a cable, without the need to screw or weld on complex brackets. Furthermore it can be installed in electrical control panels, thus avoiding complex wiring, to remotely monitor devices that often operate in harsh environments. In particular, since they are so easy to fit and put into operation, the self-powered split core current transducers can be retrofitted into existing installations without shutting down operation.
• Reliability: Solid-state transducers are more robust than electromechanical devices and require no maintenance.
• Savings: Because costs are reduced through quick, easy installation and long-term dependability.

There is an increasing number of condition monitoring technology applications that use accurate measurement and precise control of electrical parameters to achieve the required level of safety, quality, reliability and operating efficiency. But in some cases, critical status feedback comes too late or not at all, and can even result in harmful and expensive damage.

In the search for suitable sensors that, at an early stage, can provide the necessary information about the technical process, many facilities are installing electronic current and voltage transducers with integrated signal conditioning. While making the necessary measurements of the electrical parameters, these integrated transducers also provide the additional information required to ensure that reaction comes quickly and reliably. They are at the heart of many state of the art industrial supervision and automation solutions.

Characteristics and Method of Operation
Sensors used in traditional current measurement are based on the principle of a transformer with a primary winding and hundreds of secondary windings operating in short circuit. They can only measure purely sinusoidal alternating currents in the typical 50 Hz range. The measurement transducer output delivers 1 A or 5 A, which another device then has to convert into a 0 to 5/10 V or 4 to 20 mA signal.

On the other hand, an integrated transducer measures by induction (for example using a contactless Hall element) the magnetic field of an electrical cable impinged with current, and electronically processes the secondary signal to provide ready-to-use output information. These features enable the use of integrated transducers with direct current and with deformed currents.

An overview of the main differences:

Application Examples

LEM AKS integrated current transducer with relay output.

Installing integrated transducers in control panels or on electric motor drives allows monitoring the status of various kinds of electro-mechanical installations, alarm of a failure or to automatically start a backup system. For example, integrated transducers can be used in the following ways:
Safety Operations and Personnel Protection
• Personnel protection may be achieved by installing a ground fault detection sensor on the power lead.
• Maintaining safety lights on chimneys, towers and airport runways, among others, requires permanent monitoring.
Measuring the current fluctuations at the control panel is much easier to implement and more reliable than the traditional method based on photocells.

Process Control and Product Quality
• In electric dip coating systems used in the automotive industry, the anode current is measured to ensure an even thickness of coating and to define the chemical quality of the dipping paint during production.
• Measuring current during electroplating processes in the treatment of metal surfaces.
• The current consumption of a smelting furnace in the glass industry needs to be measured in order to provide specific temperature gradients over a long period.
• Monitoring current in the chemical industry in the manufacture of chemical raw materials by the application of electrolysis.

Maintenance Operations
• In electric pumps it is possible to detect whether a pump’s performance is deteriorating before it overheats or blocks.
• Integrated transducers can indicate that a cutting tool is dull and should be sharpened or replaced to avoid early (and cost-ineffective) replacement, quality issues and even damages.

Facilities and Infrastructures
• In heating, ventilation and air-conditioning applications or in high-pressure air systems, the amount of contamination on an air filter can be determined at an early stage from the level of current consumed by the fan’s electric drive.
• Battery health is monitored by measuring charge and discharge currents (up to 200 A) and leakage current (up to 10 mA) in large installations such as data warehouses and telecoms.
• The cathodic protection current is measured to monitor the effectiveness of corrosion protection equipment of concrete structures built with steel reinforced bridges, pipelines or high voltage electricity pylon.
• Measuring the current consumption of worm gear drives used to convey materials in bio-gas generation plants prevents blockages from occurring.

Energy Production and Consumption
• Monitoring DC power supplies or solar panels.
• The electric drive for the rotor blade offset in wind power plants is monitored to ensure operational safety.
• Site energy sub-metering improves energy efficiency and reduces the electricity bill as well as the environmental impacts.

Detailed Application Examples

Example 1: Monitoring a pump using a current transducer with relay output, e.g. AKS.
A blockage in a pump suction line can cause the pump to run dry, overheat and damage seals. By installing a current switch on one leg of the motor it is possible to monitor overloads (jammed pumps) or underloads (blocked suction lines).

As the illustration demonstrates, now there is no need for a pressure sensor; all the relevant information can be obtained from the real-time progression of the measured current consumption. The self-powered switch will close when the load comes on and open when the load is off.

Example 2: Monitoring the heating elements in an injection die moulding machine using a current transducer with effective value output, e.g. APR.

In a plastic injection moulding process the transducer is primarily used to monitor the heaters, because if a heating element fails, the mould will heat unevenly and affect product quality. In some cases, a progressive fault development requires continuous monitoring to detect such trends.

Installing current transducers in the heater’s control panel is much simpler, reduces the installation costs and provides much faster and more reliable fault detection.

Conclusion
As systems become more complex, so do their failure modes. Monitoring the current drawn by many different types of electrical loads allows a wide range of problems to be detected, often before they cause a system failure or have a noticeable effect on product quality. With today’s economical PLC systems and the ever-increasing choice of integrated transducers this efficient monitoring and diagnosis technology is now possible for the most diverse kinds of applications.

Condition monitoring based on the measure of current or active power consumption has generated a keen interest, and its importance will continue to increase in the future. In a trend to distribute the data processing close to the measurement devices, the integrated transducers become increasingly “intelligent”, enabling a fast response to abnormal conditions, enhanced reliability and reduced installation complexity and cost. Their integration into networked systems by means of modern communication methods allows an operator or supervision system to always have an up-to-date overview of every important parameter, even for applications that are decentralized.
Electrical parameters provide the fastest information on the condition of a system and are straightforward to measure, even when the monitored process implies severe physical constraints. Thus, integrated transducers are well suited for building reliable and cost-effective solutions for real-time process automation, supervision and control.

References
1 D. Ebenezer, E. Favre, D. Marsh, LEM Group, Switzerland, “A novel approach for AC current Measurement (PRiME)”, p 6, May 2004.
2 http://www.lem.com

For more information please visit www.lem.com.

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