Motor monitoring

One of the most common applications of induced current sensing is motor monitoring. Due to the fact that current consumption is an excellent indicator of the condition of an electric motor, current sensors can be used to solve various process control, safety, and maintenance issues.

The automation of crushers and crusher feeding mechanisms is usually achieved by installing current sensors on the motor wires. The output signal is used for closed-loop control between the crusher and the feeding mechanism. A decrease in load will indicate an increase in feed rate for the conveyor belt or loader, while an increase in load will result in a decrease in feed rate. In this operation, controlling the feed rate helps prevent paper jams, improve the uniformity or structure of the ground product, and increase the efficiency of subsequent processing operations (see Figure 4 on page 56).

The same control logic can be used to interlock two or more motors to ensure personnel safety. The purpose here is to start the second motor only after the first motor is running and driving its load. This type of safety interlock device can be used in various commercial and industrial facilities.

Automatic load switching and status alarm are also typical applications of current switches. Usually, they are used to replace auxiliary contacts that only send signals to the contactor position. Most electric motors are equipped with local isolation switches during actual load to facilitate maintenance. If the device stops running in the disconnected state, the auxiliary contacts of the contactor will give incorrect indications, which may result in serious safety or operational consequences.

Intelligent self calibrating current switches can be programmed to warn of overload and underload situations or activate backup equipment. These microprocessor based devices have built-in programmable timers that can compensate for short-term anomalies and motor surges during startup. Among these operations, the current switch is more reliable because it is not affected by contact corrosion or set point drift, and does not require regular maintenance or calibration.

Current sensors and switches are also used to ensure motor protection and simplify equipment maintenance procedures. Large electric motors require regular maintenance or reconstruction. A predictive maintenance plan based on the actual number of motor starts can ensure normal operation and reduce the risk of motor failure. Installing a current switch on the motor wire and using this signal to run a counter or feed it into an automation system can accurately count the number of starts of the motor. This information can be used to schedule preventive maintenance and reduce expensive emergency repairs.

Current sensors are also installed on cutting tools to diagnose their effectiveness. If the tool consumes too much current, its cutting edge may become dull. Sending a signal to the operator informing them of the need to maintain the program can reduce the occurrence of defective products and prevent process interruptions.