I can only imagine it has been a case of Out of Sight; Out of Mind.

There was always some anxiety about return belts eroding the steel work legs but nobody did sod all about it and just ran along on a wing and a prayer.

Thanking you for a valuable thread! ■

Originally Posted by sganesh

Dear experts,

We have installed pull cord switch ( PCS ) / Belt sway switch ( BSS ) indicators, where the conveyors lengths are very long and those conveyors are critical to production.

But some times, conveyors stop on pull cord switches /belt sway switch without any indication.

As per electrical engineers version "The time to detect number in trip indicator is about 5-6 seconds. Some times when PCS/BSS malfunctions, indicator starts processing for number display, in the meantime switch gets normalized. This makes number not displayed in indicator but actually fault is generated immediately and system is stopped. So at site no abnormality is found. "

Though this has been discussed with vendors, no fruitful solution so far.

Have you faced such problems at your site ? Kindly reply.

Regards,

A couple of things bother me about your problem:

a. are belt covers used???

Wet belts are no good for anything

b. Splicing, is it mechanical, cold cured vulcanised, hot vulcanised using either steam cured or electric resistance heat welded.

who does the splicing work?

The splice being the least bit off transmits its damage down the line over time

b1. belt manufacturer, who is it and who installed it?

c. belt age

2. belt stretching causing the belt sway related to number one

a. Do you use pulley lagging?

b. Do you use beater tail pulleys?

c. Do you use dust plows at the tail pulley return side belt?

3. WHY IS IT you do not have training idlers at every tenth troughing idler and return idler which is recommended by CCC inc.????

4. how well is are the belt flights maintained? shoveling tail pulleys, bad idlers changed, level checked, cable tension checked if needed??

HAS anyone examined the belt geometry-surveyed it since its installation? a shifted foundation for a drive or tail pulley on a single flight is a witches brew, its enought to drive one to madness and jump in the Ganges on laundry day with a paper cut!!!

If ALL the idlers are not spaced properly AND properly locked in place the belt will be fighting itself as it cannot travel linearly.

Is the ore transfered and centered in belt at the transfer point(s)???????? remember that the problems begin at the tail pulley. YOU have to train the belt empty then loaded from the tail pulley forward.

Are you using impact beds or impact idlers at the tail pulleys????

IF the belt is overloaded you will have problems and continue to have problems FOREVER ■

The problem with BSS's is the same as belt trainers - it is a lazy way to correcting an installation or belt problem.

Best way to fix your problem is to increase the detection time to prevent nuisance trips. BSS's should not be in the same circuit as a pull chord switch. As the pull chord is an "emergency stop" and therefore should not have a timer associated with it.

Also moved your post from General Aspects to a more appropriate forum. ■

Originally Posted by sganesh

Dear experts,

We have installed pull cord switch ( PCS ) / Belt sway switch ( BSS ) indicators, where the conveyors lengths are very long and those conveyors are critical to production.

But some times, conveyors stop on pull cord switches /belt sway switch without any indication.

As per electrical engineers version "The time to detect number in trip indicator is about 5-6 seconds. Some times when PCS/BSS malfunctions, indicator starts processing for number display, in the meantime switch gets normalized. This makes number not displayed in indicator but actually fault is generated immediately and system is stopped. So at site no abnormality is found. "

Though this has been discussed with vendors, no fruitful solution so far.

Have you faced such problems at your site ? Kindly reply.

Regards,

-----------------------------------------------

In ancient times (pre-1990's - 30 years ago) we observed such a problem of "signal latency" between sensor signal (pull-cords, et al.) and control protection logic. Five or six seconds is beyond the extreme. You must be able to "latch and hold" the control signal in question, typically in less than 25 milliseconds. I do not wish to deal/solve your extreme latency logic. No modern PLC program will require such conditions.

Some old Distributed Control Systems Logic (DCS) hardware may incur the signal latency, although 5 or more seconds is ridiculous. Our large (16 , 20 and 27 km Overland's (OLC), as of now) OLC have a scan time of 10-25 milliseconds to control all logic and respond to any fault with appropriate response. They are programmed to sense any of many hundreds of input data links that are done on a priority bases. A higherarcical tree is structured to report to the operator, in no more than four tiers, all events. The operator then interrogates the tree, descending in levels until the specific I/O is displayed. The tier starts with which conveyor is being tripped - the first tier. What system within the conveyor is tripped - second tier and so on. Even modern DCS systems can be programmed to regulate and response in low (< 100) millisecond cycles encumbered with all signal systems.

I would guess the programmer is practicing 1980 sequential DCS logic.

By example, the OLC may have 8-10 drives, with sensors on pulleys (heat, vibration), motors (RTD's, vibration, current, voltage, COS(phi)), reducer (oil level, temperature, flow rate, filter status), Inverters, Brakes or other speed/torque regulators with they many sensors, Holdbacks, Pull-cords, Belt Alignment, Belt Rip, Take-up Motion, et al. Many hundreds of sensors are each monitored. Faults come in multiple categories: warnings, shutdowns, Maintenance modes, Various levels of alarms such as with brakes that can partially recover from a bad sensor or other logical fault, or operate with failed assemblies (calipers, et al.). I am getting mired in the detail to emphasize the breadth of what the logic covers. This is all controlled in the 10-25 ms scan cycle.

Trying to decipher a 5-6 second logical hiatus is fraught with too many anomalies to consider an appropriate answer to your question. The conveyor's shock wave ( turning on-off a drive/brake) propagates at the speed of sound in the tensile member. In 5 seconds, the shockwave tensile reaction may travel many kilometers and apply destructive forces on the machinery, if not properly controlled.

In 1985 CDI was called to trouble shoot two OLC's - 6 and 7 km long. An electrical storm, caused the electrical shutdown of the system. Motor power was lost. The mechanical brake took about 2 seconds to fully apply. The belt speed accelerated to 135% of normal in 500 milliseconds. The brake logic hydraulics were controlled by electrical-mechanical relays with about 1 second latency. First, the brake went into normal apply mode. Then, when the first reflective wave hit in about 4-5 seconds, the wave speed pasted by the brake's mechanical control relays before they could latch. The consequence was the conveyor went into critical overspeed cooking the caliper-disk brakes, destroying the reducer and its foundation, etc.

CDI rebuilt the hydraulic system, using a B-1 bomber bay door high-speed valve with 15 millisecond latency, and programmed the PLC with special mathematics that reduced the scan application time down to less than 25 milliseconds. This resulted in a 50 millisecond overall reaction time. All of the brake anomalies were then controllable. Things have changed since 1985. Far less fancy effort is required to control large and high tension conveyors today.

Something is wrong with your control system designer. ■

As Gary says, why are you worried about Belt Sway in the normal control logic?

An appropriate dynamic analysis and system design will not produce a need for regulating belt sag. Only in an extreme emergency will the belt sag switch level become a concern. If it does reach a level of concern, the damage is already done. You cannot control extreme sag except through proper engineering. The extreme must not happen. A condition like a broken belt will produce such, otherwise not or should not. Bad drive or brakes, bad take-up response means the designer did not understand the system dynamics.

WE have never experienced a belt sag/sway measurement during any normal operating condition, including emergency stopping with multiple brake level logic in the 500 km of conveyors we have commissioned.

Lawrence Nordell on the Portal:

https://www.bulk-online.com/search?q=nordell ■

Mr. Ganesh

No where in my post did I say that BSS's are used for training the belt - they are in my opinion only on the same scale as a belt trainer in that it is a lazy way to correct a poor installation. I have seen all too often BSS's being removed from the system due to far too many nuisance trips.

BBS's are simply a make or break switch that once the belt pushes the lever to a certain point it reverses either a N/O contact or a N/C contact within the BSS. That input is then fed to your controller / PLC which then the controller determines what it will do with the input. Therefore as Larry says you need to look at your logic in the controller of the system and not at the BSS itself.

As far as whether or not they can be installed on the return side of the belt is a user's / designer's preference, there is nothing that says you can't. ■

Originally Posted by johngateley

I can only imagine it has been a case of Out of Sight; Out of Mind.

There was always some anxiety about return belts eroding the steel work legs but nobody did sod all about it and just ran along on a wing and a prayer.

Thanking you for a valuable thread!

Dear Sirs,

I have come across severe edge damage to conveyor belt due to rubbing of belt at return run on the stand posts.

This is a perennial problem with the stack yard conveyors,mainly due to uneven settlement of tracks and concrete stool holding the stand post.

To save initial cost,the soil consolidation is properly not done,instead of piling,ballast foundation is resorted to even where the soil is soft.

As a maintenance Engineer, I have fixed vertical rollers in the return side,and this has reduced the belt damage to a considerable extend.

With Regards,

Nalinakshan. ■