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This is the Annual and Quarterly Belt Scale maintenance schedule which provides information regarding recommended maintenance intervals and options available to CST Belt scale clients.

Simulation of Live Load for (Belt Weigher) Calibration.

There is debate over the best method of simulating live load, and many people have strong views on this matter. In general order of perceived increasing quality, methods of simulating live load are:

1. Electronic simulation
2. Static mass applied on the weigh frame under the belt
3. Rolling or dragging mass on the conveyor belt over the weigh frame
4. Live slugs of material which are themselves weighed on other static weighing systems such as bins or weigh bridges.

On a good weigh frame, any of these live load simulation methods will give good results (except perhaps electronic calibration). On an inadequate weigh frame; even the best methods of live load simulation will not save the situation.

Live Loads Of Material

In the case of weights and measures applications, only live loads of material are accepted for calibration purposes. This is detailed in a new document recently released by the National Measurement Institute called, NMI V7 (National Measurement Institute, an Australian Government instrumentality), a document based on the OIML (International Organisation for Legal Metrology, of which Australia is a member) document R50-1 and R50-2. The method stipulated in OIML R50 and hence NMI V7 uses a total of 10 test loads at three different flow rates, thus addresses issues of randomness (repeatability) and linearity. This is clearly the safest and most thorough method. However, it does require that there be a convenient reference scale (Control Instrument) available, and a suitable method of handling the large amounts of material involved. It is important to note that live loads or slugs of material should only be considered as a way of simulating real live load conditions because test conditions are often quite different to real operating conditions.

Electronic Simulation

The least reliable method of simulating live load is the electronic method. This is because it is based on a load cell calibration done elsewhere and then, on site, a reliable millivolt signal must be generated. This is equivalent to placing a known mass on the load cells in the weigh frame. It is not easy to produce a reliable mV signal within 1% (i.e. to the nearest 100 microvolt), often the inability to generate a reliable mV signal on site has caused this method to fail.

Additionally, the weigh frame has more parts than just the load cell. When real weight is applied, the load cell deflects and load is distributed to other parts such as alignment rods, or to large flexures. Belt stiffness may cause less of the belt weight to be experienced. The mV simulation misses all of these effects.

Another complication is that mV simulation does not recognise the inclination of a belt, making it necessary to take into account the cosine of the angle of inclination of the weigher when using electronic simulation. The actual angle of inclination needs to be measured and accounted for by means of a calculation.

These various sources of error combine to make electronic simulation notoriously inaccurate. Typical errors (from hearsay) in the industry are from 5% to 20%. This method is not recommended for any serious belt weighing application as it is as far from best practice as it is possible to be. The method of calibration checking defined by the Weights and Measures NMI V7 should be considered ‘Worlds Best Practice’.

Static Mass For Calibration

Static mass is the most popular method used for the calibration of belt weighers. The success of static mass as a calibration reference depends upon the stability and design of the weigh frame.

If the weigh frame is highly influenced by belt tension because the weigh length is too short, the weigh frame is too easily deflected, or belt tension is too high and variable, then the randomness of the system is very high. When static mass is used in this situation the calibration may well incorporate a large component of systemic error.

Another influence factor which has a very negative affect on belt weigher stability is idler friction which only affects pivoted weigh frame designs. Some pivoted systems may have as much as 2% to 3% of idler friction in their output signal. Idler friction is not a constant and changes with:

• levels and age of lubrication
• temperature
• seal drag and wear and
• changes depending upon belt condition (a large part of idler friction comes from indentation resistance which is more a characteristic of the belt than of the roller)

Weigh frames whose weight is supported fully by load cells, or by other measuring elements which all have the same sensitivity are known as the “fully suspended” type and are immune to the idler friction influence factor.

Static mass cannot fully simulate real material because it does not take into account some of the influence factors coming from belt tension and deflection that occur when load is applied through the belt. Systematic error can be relatively large due to these factors, when static mass is used to simulate live load for calibration purposes.

An experienced belt weigher manufacturer would design a weigh frame so that influence factors including belt affects are attenuated to acceptable levels. With the resulting suitably designed weigh frame, static mass can adequately simulate live load.

Calibration Chains

This is perhaps the most hotly debated means of belt weigher calibration. Many people believe that ‘calibration chains’ and sometimes ‘calibration trains’ are the definitive means of belt weigher calibration.

The calibration chain is a distributed mass which lies on the belt over the weigh frame and simulates a particular belt loading usually expressed in kg/m. The chain may consist of a series of rollers, be a series of masses on wheels, or be only a sliding mass which is tethered above the weigh frame. A ‘calibration train’ is a series of cars which run on rollers to which masses may be applied. The ‘train’ has the advantage that it allows a range of kg/m loadings to be simulated which permits linearity testing. Experience in the field suggests that calibration chains produce no better results than static mass would in a similar situation. Errors in the order of 7% have been known to occur between belt weighers which have been calibrated with chains and true weight.

The calibration chain does not simulate belt tension. This is also the main criticism of static mass, so both methods share this common and significant failing.

Unfortunately the history of the application of calibration chains has tended toward the purchase of relatively light duty, lower cost weigh frames teamed with very expensive calibration chain installations. There has been a belief that it almost doesn’t matter what the weigh frame is like, it can be calibrated with a calibration chain, which is incorrectly believed to exactly simulate live load. It is true that a calibration chain may well be a better means of calibrating a high deflection weigh frame, however, this same weigh frame will be highly unstable and its high random component of accuracy will ensure that it also holds a large component of systematic error. This scenario tends to disqualify the application from being really good for product reconciliation or for process control.

The CST World’s Best Practice Approach to Calibration

CST has long realised the importance of a suitable high quality (more expensive) weigh frame, which resists deflection, and use lower cost, lower maintenance, static calibration masses. Some customers insist on calibration chains, and we have supplied chains and static masses together on multi idler, fully suspended weigh frames. We have seen both static mass and the calibration chain agree within 0.25% on these occasions.

First, Know Your Needs:

For End Users:

Are you satisfied with your current weighers? Are high service and maintenance costs an issue for you? Are you confident in the accuracy level of your current weighers, or those you have previously worked with? Are you looking for more – higher accuracy, longer life, customisation, and solutions to specific site problems? Do you have full feedback from the site personnel on the current belt weigher/s’ performance?

For project management companies:

Do you understand the requirements for the End User? What kind of questions should you be asking (and why)? What site information do you need to ensure your belt weigher can achieve its stated accuracy?

For all belt weigher/weigh feeder enquiries, if the manufacturer or supplier does not ask for detailed information regarding the application such as location on the conveyor whether there is any existing equipment near by such as samplers or metal detectors, location of tangent points, number of feed points, distance to tail pulley, whether the belt weigher is on a straight or a curve, the length of the belt, belt tension, etc etc, then there is no guarantee that the stated accuracy will be achieved on your customer’s site.

Second, Get To Know Us, The Belt Weigher Manufacturer:

The formula for success is to find people who understand your needs and who also understand belt weighing. When there is a need to change the way your site works with belt weighers, then we would be very pleased to start the process of getting to know your needs and of allowing your people to get to know our people. One easy way to start the process is with a free site audit in which CST specialists come to your site and provide a useful review of your installed equipment. (Free Site Audit).

• We can provide access to our extensive users list and,if desired,
• . facilitate visits to some of our user sites so you can see first hand the quality of the belt weighing experience of our customers.

We have customers using our in-motion weighing systems in the mining, grain, food, ports/ship loading, rail, coal power generation, and wool scouring industries. CST has weighers certified for Trade Use in Australia, Canada, USA, and internationally through OIML.

CST have an extensive presence in Australia, within easy reach of all mine sites and we also have extensive world coverage through our agents, and by our service staff.

CST’s greatest strength is in its active partnerships with our customers from the point of enquiry, to ensure that our weighing equipment provides the accuracy solutions our customer requires, form the very beginning, and through every year of the life of the weigher.

CST understands the value of good service support, and maintains service offices at strategic places around Australia. CST service is focused only on belt weighers so our service people are true specialists who understand the special needs and challenges of belt weigher support. Our experience has shown that competent service and maintenance, using correct procedures, is crucial to ongoing accuracy performance, and avoidance of costly downtime.

Our professional engineering team is at your service backing up our service team in the field with full support and troubleshooting expertise. When difficult issues arise, CST sends its engineers out in to the field until the problem is resolved. Reliable, repeatable, accurate weighing requires a special relationship between the manufacturer and the customer. For best results, we need to form a partnership.

What each partner brings to the relationship is important for success:

The Partnership:

Our Part

• In depth engineering calculations. Analysis of site information to see whether the requested accuracy is achievable in the specified location.
• Liaison and consultation to eliminate/minimise factors affecting accuracy
• Design and manufacture of weigher robust enough to withstand harsh mining conditions, ensuring minimising/eliminating of chief cause of accuracy error.
• Ensuring trouble-free operation and minimum downtime
• Provision of skilled, trained service team to ensure equipment is fully and expertly maintained.
• Giving priority status to our Service agreement customers customers for emergency callouts and maintenance scheduling.
• Offer of free site audits and annual performance reports on weighers.
• Continual improvement of our performance – our ‘Opportunity for Improvement’ system documents all quality and performance issues on our ISO 9001 system.

Your Part

• Detailed site information, including conveyor General Arrangement drawing.
• Provide Information critical for accuracy including: position of BW on conveyor, belt tension, angle, tph
• Enjoy lower long term maintenance and replacement costs.Enjoy lower long term maintenance and replacement costs.
• Achieving provable stockpile /inventory control, thus securing ROI
• Using CST’s training services to ensure plant staff are knowledgeable about routine care of weighers.
• Entering into a CST service agreement for 3, 6 or 12 monthly in depth system check.
• Preferred customer access to the industry authority on all in-motion weighing needs .- see our FAQ on accurate weighing and BW Maintenance site, or call our sales and service managers. Report all problems or suggestions for improvement to CST, and work with us to guide our efforts to improve our products and services.

In industry,

• Good business relies on good management. Good management relies on good information.
• In the bulk handling industries,
• Good information relies on accurate measurement.
• CST – Accurate weighing for bankable ROI figures.

Belt Weighers are used for applications which really test their accuracy. If belt weighers were just flow rate indicators, the accuracy issue would be simpler; however, since belt weighers also include a totaliser upon which all the errors are accumulated, the errors can seem larger than they really are. The following discussion explains how weighing accuracy error can accumulate with a significant effect on product reconciliation, into and out of a stockpile.

Weighers Used For Stockpile Management

Stockpile management is the ideal example of the need for accurate belt weighers for product reconciliation.

Firstly, there is a need for an understanding of real belt weigher accuracies, and then an informed use of the information when used to value assets such as stockpiles. There are many horror stories about “the coal that disappeared from the stockpile” or “how the train or ship could be not loaded because the coal that was supposed to be there did not turn out to be there”. Some peoples’ careers have been unfairly affected by this basic misunderstanding of how belt weigher errors work. As with all measuring instruments, all belt weighers have two types of error

• systematic error ie. the error that’s always there; and
• . random error ie. the inability of the equipment to give exactly the same answer when measuring the same thing a second time.

A typical stockpile problem is one which has an incoming belt weigher with a 0.25% accurate belt weigher, and one reclaim belt weigher also 0.25% accurate. For this example we will consider that the two belt weighers each have a systematic error of 0.25% each, and that one is reading 0.25% high, and the other 0.25% low. Over large amounts of material, the random errors will in theory have averaged to zero.

The problem with stockpiles is that belt weighing errors add and also accumulate.

The errors from the input and output weighers will combine, even though the difference (or subtraction) of the two results is used as the stockpile figure. Worse still, this same error accumulates after the weighed material has left the stockpile.

Stockpile Errors Add And Accumulate

The error in the stockpile figure is the sum of the errors of the belt weighers used to calculate the figure. If two belt weighers are involved, each with real errors of 0.25%, then the error in the stockpile figure will be 0.5%. In terms of statistics, the random components of error (known as the variances) of the two weighers would add, but here we are speaking about a hypothetically known systemic error, and the random error component really should integrate to zero.

As material passes through the stockpile, the error we are considering remains 0.5% of the total amount of material which has passed through, it is not just 0.5% of the amount in the stockpile now. After, three million tonnes have been through a stockpile there may be theoretically 30,000 tonnes remaining. The problem is that 0.5% of three million tonnes is 15,000 tonnes. The truth is that the stockpile figure is the difference between the ‘ins’ and the ‘out’ plus or minus the sum of the errors. So the real stockpile could be anywhere between 15,000 and 45,000 tonnes.

If systematic errors can be determined, they can be adjusted to zero. The problem is that it is difficult to accurately determine the amount of coal or ore that is being moved because a reasonable proportion of it is water, and the amount of water changes over time.

Another factor in the equation is that the random errors in belt weighing don’t enter results at a high frequency, so that errors might average to zero over one day. Random errors in belt weighing are more properly called Influence Factors. Some of these have a period of one day, a week, or a year, as temperatures and seasons change.

Process Control Belt Weighers

The other major purpose of belt weighers is process control. In this role, the focus is on the indicated flow rate than in the accumulated tonnage figure.

The common belief is that a belt weigher with much lower accuracy is adequate for this role. Usually, a single idler belt weigher is chosen. However, systematic and random errors are still at work. The combined effect of these can lead to an apparent need for heavy maintenance, and errors much larger than expected.

Process Control Weighers And Accumulated Error

The process control belt weigher is at the other end of the application spectrum when compared to the ‘product reconciliation’ use. In the case of product reconciliation, final results consist of the accumulation of many measurements taken over days, weeks or even months. The result is accumulated in the totaliser. It includes all the systematic error of the belt weigher and in a sense, none of the random error. The process control application however, uses the instantaneous flow rate from the device. This output has all the random error and all the systematic error in it. As a result, and especially given the common choice of a single idler belt weigher for this role, the user has built into their process a +/-5% variability from day to day. This can hardly be helpful in controlling a process.

Belt weigher maintenance is an important issue to be considered in relation to initially inexpensive single idler belt weighers. This type of equipment is often thought to be in error (because it often is), so units are often re-calibrated. As calibration seems to change significantly, and the weigher had been in error beforehand, regular calibration is “seen” to be a beneficial routine. However, the regular calibration work is probably just moving around inside the random error of the system. The unit would be better left alone. A proper analysis of this situation would lead to the realisation that a higher quality belt weigher was a better idea, less expensive overall, and even more importantly, saves monetary losses from inaccurate weighing on an ongoing basis.

If all of the significant influence factors which bear on the ability of a belt weigher to weigh accurately through a moving conveyor belt are understood, then it becomes possible to engineer a weigh frame which has known and acceptable accuracy.

Belt width, loading, speed and belt tension, and trough angle vary widely from conveyor to conveyor. The place available to situate a belt weigher is often less than ideal, which can have a strong impact on the possibility of accurate weighing. Hence the need to adopt an ‘application engineered’ mentality rather than a merchandising approach to belt weighing.

Responsible belt weigher supply always involves an analysis of each installation. As well, the equipment which is offered will be guaranteed to work in that particular conveyor. Responsible belt weigher supply and application should always include a guarantee of the accuracy which will be achieved ‘in conveyor’.

To improve belt weigher performance, the significance of belt tension errors entering the weighing result needs to be reduced. To do this, the weigh frame needs to be longer, idler spacing greater, and the weigh frame deflection less. Chosen locations need to be where belt tension is at a minimum and has the least variability. A proper understanding of the principles alluded to in the [above diagram] becomes a powerful design tool which can be used to confidently predict belt weigher stability and performance in any situation.

With design tools based on the above principles, it is possible to guarantee performance ‘in conveyor’. As a result, instead of using industry ‘conventions’ like “four idler belt weighers are 0.25% accurate” we are able to better understand that “Different weighers are required for different conveyors to achieve the same accuracy”.

Ensuring Suitable Locations

One of the challenges for mining plant designers is to provide suitable places for accurate belt weighers.

Feed Points And Vertical Curves

The best place for a belt weigher is usually near the tail end of a conveyor, just after the feed point. Unfortunately, with the need to keep the plant compact, this is the place where a vertical curve is most likely to be needed. Vertical curves, whether concave or convex are the worst enemy of good belt weighing. The best situation for a belt weigher is on a straight piece of conveyor, with the last of the special weigh quality idler sets on the conveyor being at least 10 idler sets from the start or finish of a curve.

The problem with a concave vertical curve is that the belt often tends to lift off when the belt is empty, making it almost impossible to properly zero the weigher. Also, the belt must pass through the weighing area in a straight line; this is essential to the principle that the belt weigher should be sensitive only to forces perpendicular to the belt.

If it is not possible to avoid a curve on a conveyor which must have an accurate belt weigher, then the belt weigher will have to be located much further up the belt toward the head. Due to the fact that the belt tension is much higher (probably 100% more) than that near the feed point, a much better belt weigher will be required to achieve the same accuracy. It is quite likely that what may have required a dual idler weigh frame may now require a four idler weigh frame to achieve the same accuracy. The fact that the conveyor is more inclined at this point is of no consequence.

Long Conveyors

Long conveyors have never been a good place to locate a belt weigher. Any conveyor over about 300m long is a long conveyor and overland conveyors with lengths of 1000m or more are very long and should be avoided. No doubt it will be possible to find a belt weigher manufacturer who will say that their belt weigher will work on your long conveyor however, the belt weigher supplier will not have to live with the problems.

The two problems of long conveyors are (i)The high belt tensions involved and (ii) The fact that every test result used for calibration will usually require one complete belt revolution, this reduces the quality of maintenance and makes the calibration process very long. To zero the belt properly takes a complete belt revolution and this might be 30 minutes or more.

There are methods which can now be used to reduce the burden of having a long conveyor, these are to (i)use a special weigh frame designed for high belt tension and the other is to (ii)use special features in the belt weigher electronics to reduce the need for all calibration runs to require the circulation of the complete belt. Even when such special equipment is brought into play, it is likely that the unit will still not work as well as one on a much shorter conveyor.

At the Dalrymple Bay Coal Terminal CST have provided belt weighers for loading to ship on L5 conveyor. This belt is 8km in length and each result takes around 25 minutes. On our advice, L6 conveyor, the parallel conveyor installed in the last expansion has a much shorter belt, L6A feeding it. The belt weighers on L6A are greatly superior to those on L5 due to much lower belt tension environment and due to very quick belt revolution time.

The depth and breadth of knowledge incorporated in a product is what sets it apart from other standard products in the market place. While the end product may look or be simple, or may look similar to others competitors’ products, the real quality element comes from a very sophisticated design engineering process to ensure the product is fit for service, as well as giving excellent value over its life.

Elimination/Minimising Of Site Factors Affecting Accuracy Reliability And Repeatability

CST has a detailed and extensive knowledge of the factors that contribute to, or work against accurate weighing, in situ. Through the application of professional engineering knowledge, these problem factors can be eliminated or minimised. We do our very best to get as much detailed site information as possible from our customers, and prefer to be involved in helping determine where the weigher/weigh feeder is placed on the conveyor. In designing each weigher, our professional design engineers input detailed site information to complex engineering design processes, in order to create a weigh frame that will give the desired accuracy ‘in the field’, dealing with your site’s real world operating conditions.

Partnering Approach

We aim to have a close and ongoing relationship with our end user customers – we are not selling just a product, as much as a comprehensive service, from design, to installation, and ongoing service and maintenance. We stress this relationship, because we know that in this way our customers are getting what they want and need.

Best Value Over Life Of Unit

In terms of overall plant investment, the cost of weighing equipment is quite low, regardless of quality. CST has extensive experience troubleshooting mysterious problems that have led to a plant shut-down. These experiences reinforce very strongly our belief that upfront application of engineering design, to suit each and every weighing application, is the only way to ensure bankable accuracy, ongoing reliability, low maintenance, and avoidance of shut-downs.

Make, Install, Monitor

Our equipment, though very reliable, is not ‘set and forget’. We make it our business to ensure that our equipment is installed under our supervision and maintained with regular site attendance. This is how CST is aware of the practical needs and problems of the customer. This knowledge, combined with our ongoing investment in research and development of our products, keeps our technology at the forefront of the industry.

Accuracy Guarantee Underpinned By Strong Commitment To Integrity

Knowledge alone is not enough. Accurate weighing requires a philosophy based on strong ethical principles.

• Our business success is based on providing true data
• Therefore, at CST, we are committed to honesty at all times
• Our business is about providing trustworthy and reliable equipment
• Therefore, at CST we aim to be reliable and trustworthy ourselves.

Every company expresses its character in its products and services. It is only necessary to add to in depth knowledge and solid ethics, sufficient hard work and industry to produce excellent products and services. CST has a strong ethic of working hard to reward the trust of our customers with a good product and an overall good experience. We are not infallible, but we are strongly motivated by problems to maintain the relationship of trust with our customers by finding a satisfactory solution. The benefit to us is that we extend our knowledge through the solutions we find, and hence improve our products.

Electronics Designed To Highest Metrological Standards, Fully Remote Controlled

At a more concrete level, what is the essence of CST’s claim to be the manufacturer of the best and most advanced belt weighing systems? One significant factor is CST’s staff resources in electrical and mechanical engineering. From this professional knowledge base, we have been able to translate the customer’s performance need into a product which is very strong both electronically and mechanically. CST’s electronics used the full power of the microprocessor when it was first developed in 1984. It was not a microprocessor emulating a solid state design as so many of the competitive instruments were. The original electronics hardware and software design, with only minor changes became our trade certified belt weigher indicator. This meant that effectively, all of the electronics sets we were supplying were designed and were operating to the highest (OIML R50) metrological standards right from the beginning. Furthermore, our original product had the ability to be completely remotely controlled (via modem before the internet) and incorporated many advanced testing and calibration features which are unique in the industry, even after 25 years.

Strong, Stable Weigh Frames

From a mechanical standpoint, our mechanical engineering knowledge combined with our uncompromising quality approach have enabled us to create the strongest and most stable weigh frames in the market place. Our earliest customers have long enjoyed our high standard of belt weigher reliability and stay with us year after year, repeat purchasing our equipment for each new expansion, and installing our product enhancements and improvements along the way. As a result of our serious mechanical approach, our weigh frames were trade certifiable (OIML R50) right from the start, which is a reflection of the CST policy of providing only the best equipment. This policy has allowed us to build a sustainable business and relationships of trust with our customers.

Specifically Designed For Your Needs

The best and most advanced product is no use to the customer unless that is what they need. The basis of CST’s success is that we have not mass-produced a product which we think people want. Instead, we ask every customer, every time we receive an inquiry, what their precise needs are. As a result of asking many questions about each application, we specifically engineer a solution which fits the need, truly fit for purpose. While CST do have standard designs we have no standard products and we have no standard price list, every application is individually engineered, individually sized and individually priced. We listen to the customers, and use our knowledge, experience and professional skills to design the best and most advanced belt scale that exactly meets their need. That’s why CST Belt Weighers and Systems are the best and most advanced in the market.