From Motors and Drives

Whether it be AC or DC drive systems, maintenance of the electronic equipment is rather easy if some basic steps are followed. In this chapter, the focus will be on the preventative maintenance of drive equipment. If a drive should malfunction, some practical tips will be presented on how to find the source of the problem.

First and foremost, the focus will be on how to avoid drive problems in the first place. By integrating some simple, logical steps into a preventative maintenance program, drives can provide many years of trouble-free service. Before looking at those steps, a quick review of variable-frequency drives (VFDs) is in order.

A VFD controls the speed, torque, and direction of an AC induction motor. It takes fixed-voltage and fixed-frequency AC input and converts it to a variable-voltage and variable-frequency AC output. In very small VFDs, a single power pack unit may contain the converter and inverter. Fairly involved control circuitry coordinates the switching of power devices, typically through a control board that dictates the firing of power components in the proper sequence. A microprocessor or digital signal processor (DSP) meets all the internal logic and decision requirements.

As seen in an earlier chapter 4 (Drive Types section) a VFD is basically a computer and power supply. The same safety and equipment precautions you would apply to a computer or a power supply apply here.

© 2003 ISA

Products & Services
Gas Transmitters
Gas transmitters consist of an enclosure, sensor, and electronics that convert a signal from a gas sensor into an analog output signal (typically 4-20 mA).
pH Transmitters
pH transmitters provide electrical outputs that are proportional to potential of hydrogen (pH) inputs.
Light Curtain Controllers
Light curtain controllers send stop signals to machines that are guarded by light curtains, photoelectric transmitters that project an array of synchronized, parallel infrared light beams to a receiver.
Flow Switches
Flow switches are devices that monitor flow and send a trip signal to other devices, like a pump, for protection. These switches can be used for the measurement of gases, liquids, and steam.
Pressure Sensors
Pressure sensors include all sensors, transducers and elements that produce an electrical signal proportional to pressure or changes in pressure.

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