SPECIALISTS IN ELECTRO-MECHANICS

A R M A T U R E E L E C T R I C L I M I T E D

100 – 3811 NORTH FRASER WAY, BURNABY, BRITISH COLUMBIA, V5J 5J2

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Case Study

CoolBlue Inductive Absorber Installation

To Prevent EMI Affecting Pebble Crusher Metal Detector Nuisance Trips

CoolBlue Case Study – Pebble Crusher Metal Detector (Cont’d)

Overview

In electronics, a choke is a specially designed inductor used to block high frequency

alternating current in an electrical circuit, while passing designed frequency currents. The

name “choke” comes from "choking" higher, unwanted, frequencies. In common mode noise

situations, such as the noise generated from a VFD, noise is going out simultaneously from

all outputs, but also coupling back to earth ground. The only solution is to capture the

unwanted noise and keep it from being transmitted and coupling back to earth ground. To do

this, high frequency currents should be captured through a magnetic core. CoolBLUE is used

in this application to provide high impedance at the unwanted high frequency.

Common mode currents will cause bearing damage in the motor, and electromagnetic

interference which affects control signals, encoder feedback, and communication links for

programmable logic controllers, Remote I/O, metal detectors, pump monitors, and other

types of sensors including, ultrasonic sensors, bar code/vision systems, weight and

temperature sensors. Conducted ground current also leads to radiated emissions, with the

drive cables acting as antennas.

A mining customer was having trouble with a metal detector on their pebble crusher. They

were experiencing constant nuisance trips, and were having trouble tuning the metal detector

to pick up small enough pieces of metal that were jamming up the crusher, causing them

many downtime incidents.

It was determined that EMI coming from 2 nearby 150HP feeder motors that were controlled

by VFD’s were the cause of the issues. These motors were mounted in very close proximity

of the metal detector, in fact closer than the recommendations of the metal detector

manufacturer.

We decided to try installing CoolBlue Inductive Absorbers and NALA differential line

absorbers at the VFD’s to reduce the noise down to a level where the metal detector was no

longer affected.

Photo showing motor’s proximity to Metal Detector

CoolBlue Case Study – Pebble Crusher Metal Detector (Cont’d)

Installation and Results

Using a Rogowski Coil and Oscilloscope, the common mode currents were measured. Using a

piece of wire run through the main chokes, we are able to defeat the chokes to simulate the

currents before the chokes were installed. The Rogowski coil’s output is 50mV=1A. With the

scope set to 2V per division on 10x scale we can see current peaks over 16 Amps before and after

we have a steady current of 4 Amps. Note that the overshoots are a lot less erratic than before.

We have reduced this noise to 20-25% of the original.

CoolBlue Inductive Absorbers and NALA Differential

Line Absorbers Installed after Load Reactor

Before CoolBlue Installation After CoolBlue Installation

CoolBlue Case Study – Pebble Crusher Metal Detector (Cont’d)

The Instrumentation Lead at the mine was able to capture this shot while connected to the

Metal Detector before the CoolBlue’s were installed. The bar to the left shows a common

mode current spike and the waveform shows the metal detector’s trip reaction to the current.

This is indicative of the nuisance trips they were experiencing. After the installation of the

CoolBlue Inductive Absorbers, no more nuisance trips were experienced. The mine was also

able to tune the metal detector to pick up smaller pieces of metal, to protect the crusher from

jamming.

End of Report