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High Performance Current Sensing for Automation Applications
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This application is similar to the Heat Trace System described previously, however Snow Melt Systemsthere is a wider choice of generally lower-cost cable, which is often attached directly to roofs and gutters, or imbedded in sidewalks, steps, driveways or car parks. Although this type of installation is sometimes exempt from the code requiring ground fault protection, it is strongly recommended. The simple installation of an NK Technologies’ Ground Fault Sensor will provide an early warning of trouble. Inevitably cable insulation deteriorates with age and stresses such as hydraulic action from ground water, resulting in current leakage to ground. This may create a hazardous situation for people or animals in contact with the installation; it will waste power and cause a significant drop in the heat output and the overall efficiency and thus effectiveness of the system. The circuit may continue to function, but snow and ice could continue to accumulate. If circuit interruption is required NK’s Ground Fault Sensor should be installed in conjunction with a contactor, shunt trip breaker or other approved circuit interruption device.

Heat trace cable is used to keep pipes or their contents from freezing, or to keep Ground Fault Monitoring on Heat Trace Systemsthe contents at a constant temperature while being transferred from one location to another. The most common type of heat trace cable is the self-regulating type. Self regulating cable contains two conductors and is usually physically attached to the pipe and is therefore is subject to mechanical damage. NK Technologies’ Ground Fault Sensor are frequently installed to monitor heat trace circuits and systems. When a ground fault is detected, a circuit interruption device, like a contactor or shunt-trip circuit breaker, is used to automatically disconnect the faulty circuit. In many situations NEC and/or local electrical codes require the installation of ground fault interruption devices. However ground fault sensors are commonly installed, even if not required by code, in order to monitor the condition of the heat trace cable and installation and maintain safety. Faulty circuits can be identified and then repaired or replaced at a convenient time.

Industrial electrical heaters are prone to ground leakage due to the breakdown orInsulation Breakdown contamination of insulators. The use of NK Technologies’ Ground Fault Sensors enables early detection of leakage Currents as small as 5mA. The on/off output of the sensor can be used to trigger a circuit interruption device (for example a shunt-trip breaker) or a monitoring device like a PLC to determine the required action. Latching and auto-reset models are available in both normally energized and normally de-energized configurations suitable for most applications.

As an electric heating element ages, its resistance also changes. Many high Heater Life Predictiontechnology and extreme temperature applications employ exotic and expensive elements. Where the value of the products or materials being heated is high, the failure of a heater or heating element has a financial impact resulting from either reduced quality or scrapped materials. By measuring the current drawn by the element using an NK Technologies’ Current Transducer the resistance of the element can be determined and compared against a known ageing characteristic. When the element reaches a predetermined state it can be replaced prior to failure i.e. predictive maintenance. NK Technologies’ Current Transducers are used in conjunction with intelligent PLC systems when high power SCRs (also known as thyristors) or triacs are installed.

Heater Failure DetectionThe detection of a single phase heater failure by measuring the temperature is like measuring the effect rather than the cause. By installing an NK Technologies’ Current Operated Switch heater failure can be detected before cooling has had time to occur. The signal from the current sensor can be used to switch on a back-up heater, stop the equipment, alarm the equipment operator or trigger the appropriate action.

For 3-phase heaters installing an NK Technologies’ Current Transducer on each leg of a delta connected heating array is the best way to detect loss of one element. Unlike a typical induction motor, there will not be a substantial change in the current draw of the two adjacent phases when a heating element open circuits. The load has disappeared, and the work of heating will not be shared by the other elements. There will be a reduction in thermal output, which can take quite some time to detect with temperature sensors like thermocouples. A current transducer will identify the problem in milliseconds! Poor product quality can be prevented and large quantities of raw material can be saved by quick action.

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