High Performance Current Sensing for Automation Applications
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Snow Melt Systems

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.

Ground Fault Monitoring on Heat Trace Systems

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.

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.

DC Motor Installations

Many applications requiring high torque at low speeds, like bridge cranes and log DC Motor Installationscarriages, use DC shunt wound motors. Since it is relatively easy to control the speed of a DC motor by adjusting the voltage to the field windings, precise regulation is afforded to applications like printing press paper feeds or web control of multiple motors in the paper making process. Using an NK Technologies’ DC Current Transducer will provide an analog signal that can be used to keep the motor from over-current situations. Using an NK Technologies’ DC Current Operated Switch will insure that if the motor field supply is lost, the motor will not over-speed to the point of self-destruction.

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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