Controls

The speed control is designed to operate with a magnetic drive equipped with a magnetic pickup. The controller contains a signal isolator to allow precise speed adjustment from an automatic 4-20 ma (milliamperes) of 0-10 VDC (volts DC) control signal. The control has a closed loop control circuit, field firing circuit, current feedback loop, and SCR (silicon-controlled rectifier) power stage for controlling the output speed of the magnetic drive. The control also has an acceleration/deceleration ramp circuit that is an integral part of the control circuit for smooth acceleration of the load—especially important for many types of pump loads.

The input signal is fed through an isolation circuit or from the manual speed adjustment pot to the controller circuit. The controller circuit outputs a regulated voltage and current to the field firing circuit. This voltage/current output is also regulated by the current feedback sensed by the resistor network and the speed signal from the magnetic pickup to assure precise speed regulation. The field firing circuit regulates the firing timing of the SCRs. By using multiple loopback feedback circuits, speed regulation is held with .2% of the set speed.

The controller circuit has a current limiting adjustment that controls the maximum current from the SCR circuit to the drive field to eliminate any excess current in the drive coils. This protects from overpowering the drive and causing unnecessary heating.

The controller power circuits convert 120-480 VAC (volts AC) into DC voltage. The DC voltage is converted to the required voltage of the drive field by the SCR firing circuit using pulse width modulation. The circuits are protected by circuit breakers and metal oxide varistors.

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Survival Treasure

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