High Performance Current Sensing for Automation Applications
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Isolated Alarm System Interfacing

If an alarm or monitoring system is to be installed adjacent to another, (for Isolated Alarm System Interfacingexample: a municipal hurricane or tornado warning system) it is desirable to tie in to it. This can be achieved by the utilization of an NK Technologies’ Current Operated Switch (The split-core version is ideal for this). The switch simply detects current flowing in a conductor to say the audible or visual alarm providing a fully isolated ‘repeater’ signal. Switches are available for both AC and DC applications.

Equipment Ground Fault Monitoring

As we become more aware of occupational health and safety so the need for Equipment Ground Fault Monitoringprotection against ground faults is growing. Industrial electrical equipment is fed via a distribution system which in turn is connected to a main feed. Ground fault protection may be installed, for instance at a main breaker, protecting the branch circuit but not necessarily a valuable or critical piece of equipment. Industrial Ground Fault Sensors from NK Technologies are designed to be installed in individual pieces of equipment or their electrical feed. The sensors provide an on/off output that may be used to operate a circuit interruption device like a shunt trip breaker or feed into an alarm system. With over 100 models to choose from, there’s sure to be one to fit your application.

Heater Failure Detection

The detection of a single phase heater failure by measuring the temperature is like Heater Failure Detectionmeasuring 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.

Vacuum Pump Monitor

Vacuum pumps are used in a variety of applications in the semiconductor industry, Vacuum Pump Monitorheat treatment, plastics and packaging industries. By adding an NK Technologies’ Current Transducer over the lead feeding a vacuum pump, it can easily be determined when all the air has been removed from a vessel or envelope. The analog output can signal the vacuum or equipment controller that it is time for the next step in the process. In the case of an automated packaging machine, a drop in current will signal that the package is ready for sealing.

Moisture Ingress on a Submersible Pump Motor

An NK Technologies’ Ground Fault Sensor installed on a submersible pump motor provides Submersible-Pump-Motoran easy to install replacement or addition to moisture sensors housed in the motor casing. Unlike moisture sensors that have to be wired back to the motor control center, the GF sensor is installed in the motor control center. By detecting the ground fault current resulting from moisture ingress or other potentially dangerous condition remedial action can be taken prior to catastrophic failure. Either the pump can be replaced at the next convenient time or switched off and a back-up pump started.

Pump Load Monitoring

NK Technologies’ Current Transducers are used to monitor motor current and Pump Load Monitoringtherefore motor load. The output from the transducer may be fed to an analog or digital indicator or a Programmable Logic Controller (PLC) for more sophisticated monitoring and control.

NK Technologies’ Power Transducers provide load monitoring in more critical applications where the addition of voltage measurement and the determination of the phase relationship between current and voltage (power factor) provides more control.

NK Technologies’ Ground Fault Sensors keep the pumps safe by measuring ground leakage currents as low as 5mA. This also provides an alternative to moisture sensors used with submersible pump motors.

Also see these other articles:
Pump Jam & Suction Loss
Moisture Ingress on a Submersible Pump Motor

Pump Jam & Suction Loss Protection

Pumps can become jammed due to foreign matter and cause damage to both the Pump Jam & Suction Loss Protectionpump and the motor before thermal overloads are tripped. Additionally a blockage in the suction line of the pump can cause the pump to run dry, overheat and break a seal.

By simply installing an NK Technologies’ self-powered Current Operated Switch in one leg of the motor overload (pump jam), underload (suction loss) or underload & overload can be detected quickly before damage occurs.

Status Alarming

The auxiliary contacts in a motor starter are commonly used to indicate when the Status-Alarmingmotor is running. However, auxiliary contacts only indicate the position of the contactor, not the actual load status. If a downstream disconnect is open (for example, for maintenance) or the contact fails (either sticks or dirt build-up) there can be serious consequences.

At a large fish farm, failed aerator pumps resulted in massive stock losses. Because the auxiliary contacts remained closed when the pump failed, the alarm was never activated, the back-up pumps were not switched on and the fish suffocated due to lack of oxygen. Now NK Technologies’ Current Operated Switches have been installed to provide an alarm signal and a signal to automatically switch over to the back-up aerator pumps.

Closed Loop Control

Normal linear AC induction motors have a current characteristic that increases with Closed Loop Controlload. Thus a measurement of current is proportional to the motor load. NK Technologies’ True RMS Current Transducers are designed to work in conjunction with variable frequency drives (VFD) and measure the current in the leg of the motor.

At an engine block manufacturing facility NK Technologies’ Current Transducers provide the input to a PLC used to position the rotating wire brushes in order to clean away burrs and debris after machining. As the current, and thus the load, changes so the brushes are positioned for optimal clean-up. Similarly Power Transducers are used to control the position of wheel wash brushes in a carwash. Power measurement provides a more linear relationship for motors and other loads with non-linear current characteristics. Current Operated Switches are used to co-ordinate operations between conveyor, washing and drying systems.

Conveyor Jam Protection

Conveyor Jam ProtectionWhen conveyors jam and the drive motor continues to run, expensive mechanical damage to the drive components often occurs. By installing an NK Technologies’ Current Operated Switch an overload condition, detected by higher than normal running amps, can be used to switch off power to the motor before mechanical damage results. The switch setting can be adjusted so it is not affected by normal changes in conveyor load. Current operated switches are the modern day equivalent of less reliable electromechanical jam relays that have been in use for many decades.

In situations where there may be large variations in load an NK Technologies’ Current Transducer may be used to feed motor amps to the conveyor control system, commonly a PLC. The PLC may be programmed to accommodate different setpoints for different mechanical loads so that jam protection is provided from light to heavy loads. In situations where the conveyor is not able to accept analog signals NK Technologies has developed a patented transducer with a frequency output suitable for the Digital Inputs of most PLCs.

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