Dear Mr. Bruce,

The easiest way to know the tension in belt is to install load cells on anyone pulley mounting and its reading is to be converted into belt tension. The output from load cell can be displayed as belt tension, and it can also be utilised to monitor the system. For example, if the tension is below the minimum level or it is more than the maximum allowed, it will automatically not permit the operation (the tension in the belt always fluctuates and hence this monitoring action can be when conveyor is not running).

Please contact load cell manufacturers / suppliers or conveyor manufacturers in your country and they should be able to do this job easily.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor

Email : parimul@pn2.vsnl.net.in ■

Mr.Mulani:

I am forming this response to the general design of belt conveyors more than the direct query of buckwheel design.

You have formed a response to a question that assumes the operator has not heard of takeup load cell control. You may be right. If you are not. I say your answer leaves a lot to be desired. Certainly load cells are used on the ropes and on the carriage systems. What do the tensions tell you about the conveyor's SAFE operating conditions? Very little, unless you are aware of the dynamic forces captured by a fixed takeup.

When the loaded conveyor stops, using a fixed takeup ( or moving very slowely), large forces are applied to the slack side tension. Typically, they are equal to about have the head drives TE ( taking liberty to assume a head drive). One half become a positive stress/strain shock wave and half a negative wave that move in opposition. For an incline belt, the carry side sees a TE/2 compression shock wave and the return strand sees TE/2 tension shock wave. The return strand shock wave arrives at the tail before the carry side causing a large force of many times the steady-state force ( adding the steady-state tail force and TE/2). This is a normal design problem for the engineer of such systems.

Beware, the tail force dynamics can be much higher than this conditions, but it is a start.

If you apply auto-control logic to the typical winch or hydraulic takeup during a stop, you then create a second big problem. During starting, after such a stop, you may not be able to generate sufficient takeup force to prevent drive slip. How much do you need? This can only be calculated based on the strain released and its disribution. Not possible. Therefore, the practice is to lock the takeup during a stop as is done in the German lignite mines.

So, the point of this diatribe is to debunk the simplistic answer that the loadcell or other transducer device will give the operator meaningful decision tools to operate the belt in a safe manner wiothout knowing much more about the true dynamic conditions.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Dear Mr. Nordell,

Load cell is a convenient / economical means (item) to measure tension / force. It needs to be appropriately adopted for conveyor application. I have also hinted that tension in belt is different under varied situation, and is to be taken care. The user’s question is in context of small length conveyors.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in ■

Side Note on Load Cell Control of Takeups

Load cell control has an achilles heel. Some of the electronic componenets can fail in such a way as to produce a runaway condition if the takeup is placed in auto-control. The micro-strain produced by the strain gauge must be amplified. Electronics in the transducer can fail producing a command signal to increase or decrease the set tension to an unlimited value. Diodes and operational amplifiers fail either dead short or non-conductive with equal probability. This has been observed many times in operation. The result is to have a slack or overtension state.

The solution is to apply manual control as is practiced in Germany.

Lawrence Nordell ■

Dear Ronalds,

For effective monitoring & correction of the belt tension , I use winch take-up with load sensing device.Load cell will give indication of tension status & the same will be hooked up with its drive for correction.

Atanu Banerjee ■