KB Category Archives: Aggregates/Cement

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.

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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.

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Crusher/Grinder/Shredder Motor Interlocks

CrusherGrinder2The performance of size reduction equipment like crushers or grinders can be optimized by controlling the in-feed in order to:

  • Help prevent jamming
  • Improve the uniformity of the resultant product
  • Enhance overall production efficiency

By installing an NK Technologies’ Current Transducer or Power Transducer to monitor the in-feed to a crushing process, the speed of the in feed drive can be slowed when the crushing motor is working too hard, or the speed can be increased when the crusher is under worked. The analog 4-20mA proportional signal is fed directly into a VFD, and the drive does the rest of the control.

Additionally, NK Technologies’ Current Operated Switches installed on other conveying motors can be used to signal malfunction (for example over-load or motor failure) to help prevent costly equipment damage.

NK technologies current sensors come in a variety of configurations for quick and simple installation either for the OEM or End-User.

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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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Heater Failure Detection

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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Pump Jam & Suction Loss Protection

Pump Jam & Suction Loss ProtectionPumps can become jammed due to foreign matter and cause damage to both the pump 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.

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Fan Status: Independent Verification of Operation

Fan Status: Independent Verification of OperationGood engineering practice suggests that every control output should have a corresponding status input for verification. On fans and pumps a current operated switch can be snapped over one motor leg and the output fed to the automation system. NK Technologies’ self-powered Current Operated Switches will close when the motor turns on and open when the motor is off.

By adjusting the setpoint pump coupling or fan belt failure can be detected. This reliable solid-state solution eliminates the need for unreliable pressure current switches and their costly installation.

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