Electronic ear in SAG mill

  • Thread starter Vega M. Hernan M.
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Thread Starter

Vega M. Hernan M.

Hi List:

We have an application in a SAG Mill where we have installed an electronic ear in order to listen the noise produced by the balls falling to the bottom of the mill. Our idea is to convert the amplitude and frequency of noise to a 4-20mA signal (or something else) in order to determine if the ball is crushing the mineral or the mill lining. Any help will be appreciated.

Many thanks,

Hernan Vega

Al Pawlowski, PE

Sounds like a fun experiment. Lots of low-cost (some free) audio range spectrum analysis programs for PC's out there. Search some of the
on-line download libraries. One of these might be worth trying to see if you can get some correlations to work with.

Mark Blunier

You might want to take a look at Milltronics Senaco.

Mark Blunier
Any opinions expressed in this message are not necessarily those of the company.
In response to Vega M. Herman's query.

Although you are looking for an electronic method, the folllowing may be useful:

Many, many, years ago while working in a gypsum plant, I remember that tube mill crushing plant operators would listen to noise emissions via a
block of wood held between the ear and the machine.

Perhaps signature analysis of an audio signal, vibration sensor, or the drive motor's load current (or power) might provide you with the
information you seek.

Phil Corso, PE
Trip-A-Larm Corp
Further to my earlier reply to Vega M. Hernan's query:

I also remember a very detailed, but fascinating, mathematical analysis of the ball & ore movement thru the mill and its impact on the drive motor and power transmission train (motor, gearbox, drive shaft). It was presented in a monthly magazine related to the materials handling

Unfortunately, I can't recall the article title nor the magazine. The period was between 1955 and 1960.

Phil Corso, PE
Trip-A-Larm Corp

David Fernandez

This application of electronic ear is used to control the mass of mineral that is possible to mill. It's usually used in cement industry. This control loop is inverted; so if the sound decressed, the feed of the mill has to decressed. Also this measure is used to generate an alarm that cut the feed of the mill to avoid excess of mineral.

Another strategy to control the mineral feed is to control the electric current or power of the elevator. The current is a meassure of mineral mass milled. If you control the current with the mill feed you'll reach a stability of the mill. The electronic ear is a good measure for alarm but
not for control.

I hope i can help you

David Fernandez de Miguel
Madrid . Spain
e-mail: [email protected]
As an apprentice electrician I was taught to use the same method to check for wear on bearings on electric motors. We didn't use a block of wood. We
actually used a large screw driver (with the blunt end to the ear of course!).

If the blade of the screwdriver is placed on the equipment casing, near the bearing, and the handle pressed against your earhole, you can get a good idea of the condition of the bearing. This may have been the first high-tech condition monitoring tool. NOT!

Mark Fairbaugh

We use electronic ears here on Sag mills. The signal is converted to 4-20 and goes into the PLC and is transfered to the DCS and Expert Control system.

The sound is used to check that the balls are hitting material and not the liners. If the sound level increases the feed is increased to bed the mill some more to prevent liner damage due to the balls striking against them.

The ears and transmitters are from Svedala. They do not read a decibel reading but an arbitrary number based on the level of sound that we have determined to be our baseline.

If you have any questions about the setup or operation please let me know.


Mark Fairbaugh
PT Newmont Nusa Tenggara
Sr. Process Control Engineer
e-mail: [email protected]
Phone: (62)-370-636-318 Ext. 47948
David Fernandez de Miguel wrote:

>........The electronic ear is a good measure for alarm but not for control........

Have heard of many successful control applications of this technology used anywhere material is being crushed e.g. in Ball Mills. General concept:
Large "rocks" tumbling around are very rich in Low Frequency but as milling progresses and "rocks" are pulverized into "sand" the frequency shifts to the upper end of the audio spectrum. An "1/3 Octave Filter" matched to the acceptable "Voiceprint" of the process is then used as an endpoint detector.


Tony Firth, Electrical Eng.,
Quester Technology Inc.,Fremont,CA
Nordberg is a supplier of all types of grinding mill systems to the gloabl mining market. We supply acoustic response based control systems for tumbling mills of all types, including SAG mills as an aftermarket product. You can contact me for more information.

[email protected]

Can the control based on the electronic ear be added to conventional SAG Mill bearing pressure based control for better performance?