To the old adage “the only certain things are death and taxes” should be added “…and spiralling energy costs”. One of the most significant costs in production of most bulk solids is the amount of energy consumed to produce it. This is particularly relevant in products such as graded quarry products, black top, and processes that use dryers and heaters in the process. In quarrying where primary, secondary and tertiary crushing is used the costs can be astronomical.
The cost per unit weight, (in the case of quarries per unit tonne) must be known, as this cost has to be passed on to the customer. A significant part of this costing is how much energy was used to produce the product. In order to do this on an accurate day to day basis, measurements need to made on the plant. If the requirement for this measurement is on a real-time basis then one of the best ways to achieve this is to use belt weighers. Belt weighers produce real time and long term information about mass flow within a plant. Belt weighers can also be sited between various pieces of equipment in order to monitor individual items of interest.
Power Monitoring
The information that is produced by the weigher as well as the power monitoring system needs to be collected and correlated to the power consumption over the same measurement period. Measuring electrical power used is a fairly straightforward process, using a power meter with analogue and pulse outputs giving instantaneous power and integrated kW/hr pulses. The output from these units can also give useful information such as peak demand, phase balance and line voltages and much else.
If a relatively simple unit is employed with pulse output only, the frequency of the pulses can be translated into real-time power consumption in kWhrs. Depending on the sophistication of the unit, they are fairly cheap and easy to install. CTs are used to interface to the 3phase supply giving good galvanic isolation between the power supply and the monitoring system.
Correlating the Information
So what is the best way to correlate all the information produced by the plant transducers, and make the information easy to read and valuable for analysis of plant performance? It is important that the data from the Belt Weigher can be read in the same time frame as the information from the power monitoring system.
Data Loggers
Lodestone use multi-channel data loggers to store assess and display this information both in real time and as historical data. The data is time and date stamped. The frequency that the data is recorded is programmable. Depending on the memory size within the logger, in excess of 12 months of information can be stored and accessed. The information can be displayed in real-time on a PC and stored to disc for later analysis. The data can either be transmitted via a serial link (RS232 or USB) or downloaded from a Data Stick which can be plugged into the data logger, and removed when the information is required and plugged directly into a PC. This obviates the need for wiring and also the need for a dedicated PC connected to the system. The information collected can then easily be transferred into an Excel spread sheet or similar for further analysis. A basic spreadsheet is supplied with the data logging system.
Data Logger Flexibility
The advantage of using data loggers is that other plant transducers can be introduced into the system at very little extra cost. If you have industry standard process signals such as 4-20 mA, pulses, frequency, Thermo-couples et al, then all of these can be monitored. The data logger has essentially become a modern day equivalent to the chart recorder with the added flexibility of being able to easily manipulate the data collected on a PC.
System Accuracy
As with all measurement systems the information being produced has to be accurate and repeatable. (Rubbish in equals Rubbish out). To achieve this is not always easy. When designing a belt weigher installation on a plant, the method of calibration should always be considered carefully. The only way to properly calibrate a belt weighing system is by live load checks. That is to say by running a known amount of material over the weigher and checking the actual amount conveyed to the measured amount. This material can be either pre-weighed or post-weighed ideally over the site weighbridge. Failing this the use of a pre-calibrated front-end loader weigher can be used, but this is not always as accurate as a stamped weighbridge.
Calibration Methods
Using calibration weights, chains or material belt cuts simply isn’t good enough is the result is important to the final price calculations. One of the major reasons for using material weigh checks is that the weigher is tested under actual operating conditions. This takes into account such problems as change in belt tension, conveyor deflection under load and no load condition and belt tracking empty and full. All these variables and others can cause weighing errors. Weights and chains do not provide these effects and tests using material belt cuts have to be done with the belt stopped. A belt weigher will show different weights on the loadcell in static and dynamic conditions mainly due to the difference in belt tension. Also the ratio of material from a belt cut against the amount of material conveyed is considerably different and the resolution is too low for the results to be really useful. It can only put the weigher into roughly the correct area of calibration.
All methods other than weighed load check can only show the weigher is “about” right.
Customer Confidence
There is also another very important aspect in using weighed load checks in that it actually proves that the weigher is performing correctly. The user has to be confident that the information generated by the weigher is correct.
Frequency of Calibration
When asked about the frequency of checks, we always say as often as you can and until you are confident that the weigher is holding its calibration over a useful period of time. This then usually translates to a check maybe once every 3 months depending on the site. If the weigh area is kept free of spillage and is regularly inspected, I would expect the calibration to hold for a minimum of 3 months. Usually site personnel get a feel if the numbers produced are correct.
Site Surveys
It is important that in a critical application, a site survey is carried out in order to establish whether the conveyor in question is suitable for a belt weigher. The person doing the survey should have an in-depth knowledge of weighing system applications and should be able to advise his potential customer what if any modifications need to be made in order to achieve the accuracy and repeatability required.
Accuracy Statements
To give accuracy statement of say ±0.5% without giving a length of time that the equipment will hold this accuracy is meaningless. Most belt weighers will give a good result at the time of testing. The real test is how long will the system hold this accuracy. It should be one of the first questions asked when purchasing a belt weigher. The only way to assess this is to inspect the site and calculate from information accrued what weigh length is required to give a short, medium or long term accuracy.
The conveyor conditions are crucial for good belt weighing. Some are listed below:
• The conveyor should be rigid in the weigh area. There is no way round the word “rigid”. Any structural deflection in the weigh area can cause weighing errors.
• Ideally the belt tension should be controlled by a Gravity Tension Unit ( GTU ) or other device that keeps the tension as constant as possible.
• The belt weigher should be sited at the non-driven end of the conveyor. This would normally be the tail end. This part of the conveyor tends to have the least change in tension. It should be far enough away from the feed point so that the material has settled before it reaches the weighing area.
• The conveyor should be as full as possible. ( Volumetric Utilisation )
• The troughing angle should be as small as is practical. The steeper the troughing angle the stiffer the conveyor.
• The conveyor speed should be as low as possible. The longer the weigher has to measure the product on the conveyor the better the measurement will be. Higher belt speeds demand longer weigh lengths if a reasonable weighing accuracy is to be maintained. This is known as material resident time in the weigh area. There are a number of other factors that govern the weigh length. My last article “The Black Art of Belt Weighing” dealt with these problems (see https://forum.bulk-online.com/showth...p?postid=23543).
Long Term Calibration
Another method that we have employed successfully when we cannot run a weighed check is to use long term calibration. This involves the user keeping records of both the belt weigher throughput and the weighbridge totals. Over a period of weeks and months the two can be correlated and a calibration figure calculated.
Belt Zero
One of the major indicators of the performance of a belt weigher is the belt zero. When the belt is running empty, the rate reading should be showing a negative and positive reading as the weight of the belt changes along its length. The belt zero should be checked each day as this is usually a major source of inaccuracy. A belt zero measures the weight of the belt over a pre-determined number of revolutions and calculates the average zero. This value then becomes the “zero” value. We have often been asked if this process could be done automatically. The answer is yes, but we don’t recommend it. A belt weigher can never be a “Fit and Forget” device as there are too many variables that can effect it performance.
Auto Zero Tracking
The LodeMaster belt weigher has an Auto Zero Tracking (AZT) option built into the system. When this function is selected the system monitors the amount of material flowing over the weigh area. When this amount of material drops below a predetermined amount, the AZT function begins to operate. This is known as the Dead Band. This is the point when integration ceases and is software programmable by the user. The system then allows the belt to travel for a number of revolutions and if during this time the system stays within the Dead Band, an automatic Belt Zero routine is instigated. This is similar to the manual zero routine selected via the keypad. If during the AZT routine the system remains within the Dead Band then at the end of the period a new Zero is stored by the system. If the Zero passes out side the Dead Band then the AZT routine is aborted. This process will continue until material is flowing on the belt. The disadvantage of using AZT is that if there is a trickle of material on the belt or a there is a build up of material on the weigh bridge which then falls off, weighing errors can be introduced and the zero can elevate beyond the prescribed limits. If this occurs, the AZT is then cancelled an alarm is shown. This alarm then usually means a phone call to the vendor in order to establish if the weigher is still functioning correctly. It is far better to perform a manual zero with someone observing what is taking place.
Plant Tuning
Once it has been established that the transducers are performing accurately and repeatably, then the information generated in real time can be invaluable. Just a small change in feed rate to various pieces of plant can be monitored to assess if the change increases or decreases the plant efficiency. Similarly a more efficient gearbox may be added to a system and the results can be read in real time. The possibilities are endless. The combination of Belt Weighers and other plant transducers produce a very powerful management tool. “To measure is to know”.
For more information on Lodestone Electronics Ltd., please visit:
Belt Weighers and Energy Monitoring
Belt Weighers and Energy Monitoring
by
Jon Scarrott CEng MIET
Managing Director
Lodestone Electronics Ltd
To the old adage “the only certain things are death and taxes” should be added “…and spiralling energy costs”. One of the most significant costs in production of most bulk solids is the amount of energy consumed to produce it. This is particularly relevant in products such as graded quarry products, black top, and processes that use dryers and heaters in the process. In quarrying where primary, secondary and tertiary crushing is used the costs can be astronomical.
The cost per unit weight, (in the case of quarries per unit tonne) must be known, as this cost has to be passed on to the customer. A significant part of this costing is how much energy was used to produce the product. In order to do this on an accurate day to day basis, measurements need to made on the plant. If the requirement for this measurement is on a real-time basis then one of the best ways to achieve this is to use belt weighers. Belt weighers produce real time and long term information about mass flow within a plant. Belt weighers can also be sited between various pieces of equipment in order to monitor individual items of interest.
Power Monitoring
The information that is produced by the weigher as well as the power monitoring system needs to be collected and correlated to the power consumption over the same measurement period. Measuring electrical power used is a fairly straightforward process, using a power meter with analogue and pulse outputs giving instantaneous power and integrated kW/hr pulses. The output from these units can also give useful information such as peak demand, phase balance and line voltages and much else.
If a relatively simple unit is employed with pulse output only, the frequency of the pulses can be translated into real-time power consumption in kWhrs. Depending on the sophistication of the unit, they are fairly cheap and easy to install. CTs are used to interface to the 3phase supply giving good galvanic isolation between the power supply and the monitoring system.
Correlating the Information
So what is the best way to correlate all the information produced by the plant transducers, and make the information easy to read and valuable for analysis of plant performance? It is important that the data from the Belt Weigher can be read in the same time frame as the information from the power monitoring system.
Data Loggers
Lodestone use multi-channel data loggers to store assess and display this information both in real time and as historical data. The data is time and date stamped. The frequency that the data is recorded is programmable. Depending on the memory size within the logger, in excess of 12 months of information can be stored and accessed. The information can be displayed in real-time on a PC and stored to disc for later analysis. The data can either be transmitted via a serial link (RS232 or USB) or downloaded from a Data Stick which can be plugged into the data logger, and removed when the information is required and plugged directly into a PC. This obviates the need for wiring and also the need for a dedicated PC connected to the system. The information collected can then easily be transferred into an Excel spread sheet or similar for further analysis. A basic spreadsheet is supplied with the data logging system.
Data Logger Flexibility
The advantage of using data loggers is that other plant transducers can be introduced into the system at very little extra cost. If you have industry standard process signals such as 4-20 mA, pulses, frequency, Thermo-couples et al, then all of these can be monitored. The data logger has essentially become a modern day equivalent to the chart recorder with the added flexibility of being able to easily manipulate the data collected on a PC.
System Accuracy
As with all measurement systems the information being produced has to be accurate and repeatable. (Rubbish in equals Rubbish out). To achieve this is not always easy. When designing a belt weigher installation on a plant, the method of calibration should always be considered carefully. The only way to properly calibrate a belt weighing system is by live load checks. That is to say by running a known amount of material over the weigher and checking the actual amount conveyed to the measured amount. This material can be either pre-weighed or post-weighed ideally over the site weighbridge. Failing this the use of a pre-calibrated front-end loader weigher can be used, but this is not always as accurate as a stamped weighbridge.
Calibration Methods
Using calibration weights, chains or material belt cuts simply isn’t good enough is the result is important to the final price calculations. One of the major reasons for using material weigh checks is that the weigher is tested under actual operating conditions. This takes into account such problems as change in belt tension, conveyor deflection under load and no load condition and belt tracking empty and full. All these variables and others can cause weighing errors. Weights and chains do not provide these effects and tests using material belt cuts have to be done with the belt stopped. A belt weigher will show different weights on the loadcell in static and dynamic conditions mainly due to the difference in belt tension. Also the ratio of material from a belt cut against the amount of material conveyed is considerably different and the resolution is too low for the results to be really useful. It can only put the weigher into roughly the correct area of calibration.
All methods other than weighed load check can only show the weigher is “about” right.
Customer Confidence
There is also another very important aspect in using weighed load checks in that it actually proves that the weigher is performing correctly. The user has to be confident that the information generated by the weigher is correct.
Frequency of Calibration
When asked about the frequency of checks, we always say as often as you can and until you are confident that the weigher is holding its calibration over a useful period of time. This then usually translates to a check maybe once every 3 months depending on the site. If the weigh area is kept free of spillage and is regularly inspected, I would expect the calibration to hold for a minimum of 3 months. Usually site personnel get a feel if the numbers produced are correct.
Site Surveys
It is important that in a critical application, a site survey is carried out in order to establish whether the conveyor in question is suitable for a belt weigher. The person doing the survey should have an in-depth knowledge of weighing system applications and should be able to advise his potential customer what if any modifications need to be made in order to achieve the accuracy and repeatability required.
Accuracy Statements
To give accuracy statement of say ±0.5% without giving a length of time that the equipment will hold this accuracy is meaningless. Most belt weighers will give a good result at the time of testing. The real test is how long will the system hold this accuracy. It should be one of the first questions asked when purchasing a belt weigher. The only way to assess this is to inspect the site and calculate from information accrued what weigh length is required to give a short, medium or long term accuracy.
The conveyor conditions are crucial for good belt weighing. Some are listed below:
• The conveyor should be rigid in the weigh area. There is no way round the word “rigid”. Any structural deflection in the weigh area can cause weighing errors.
• Ideally the belt tension should be controlled by a Gravity Tension Unit ( GTU ) or other device that keeps the tension as constant as possible.
• The belt weigher should be sited at the non-driven end of the conveyor. This would normally be the tail end. This part of the conveyor tends to have the least change in tension. It should be far enough away from the feed point so that the material has settled before it reaches the weighing area.
• The conveyor should be as full as possible. ( Volumetric Utilisation )
• The troughing angle should be as small as is practical. The steeper the troughing angle the stiffer the conveyor.
• The conveyor speed should be as low as possible. The longer the weigher has to measure the product on the conveyor the better the measurement will be. Higher belt speeds demand longer weigh lengths if a reasonable weighing accuracy is to be maintained. This is known as material resident time in the weigh area. There are a number of other factors that govern the weigh length. My last article “The Black Art of Belt Weighing” dealt with these problems (see https://forum.bulk-online.com/showth...p?postid=23543).
Long Term Calibration
Another method that we have employed successfully when we cannot run a weighed check is to use long term calibration. This involves the user keeping records of both the belt weigher throughput and the weighbridge totals. Over a period of weeks and months the two can be correlated and a calibration figure calculated.
Belt Zero
One of the major indicators of the performance of a belt weigher is the belt zero. When the belt is running empty, the rate reading should be showing a negative and positive reading as the weight of the belt changes along its length. The belt zero should be checked each day as this is usually a major source of inaccuracy. A belt zero measures the weight of the belt over a pre-determined number of revolutions and calculates the average zero. This value then becomes the “zero” value. We have often been asked if this process could be done automatically. The answer is yes, but we don’t recommend it. A belt weigher can never be a “Fit and Forget” device as there are too many variables that can effect it performance.
Auto Zero Tracking
The LodeMaster belt weigher has an Auto Zero Tracking (AZT) option built into the system. When this function is selected the system monitors the amount of material flowing over the weigh area. When this amount of material drops below a predetermined amount, the AZT function begins to operate. This is known as the Dead Band. This is the point when integration ceases and is software programmable by the user. The system then allows the belt to travel for a number of revolutions and if during this time the system stays within the Dead Band, an automatic Belt Zero routine is instigated. This is similar to the manual zero routine selected via the keypad. If during the AZT routine the system remains within the Dead Band then at the end of the period a new Zero is stored by the system. If the Zero passes out side the Dead Band then the AZT routine is aborted. This process will continue until material is flowing on the belt. The disadvantage of using AZT is that if there is a trickle of material on the belt or a there is a build up of material on the weigh bridge which then falls off, weighing errors can be introduced and the zero can elevate beyond the prescribed limits. If this occurs, the AZT is then cancelled an alarm is shown. This alarm then usually means a phone call to the vendor in order to establish if the weigher is still functioning correctly. It is far better to perform a manual zero with someone observing what is taking place.
Plant Tuning
Once it has been established that the transducers are performing accurately and repeatably, then the information generated in real time can be invaluable. Just a small change in feed rate to various pieces of plant can be monitored to assess if the change increases or decreases the plant efficiency. Similarly a more efficient gearbox may be added to a system and the results can be read in real time. The possibilities are endless. The combination of Belt Weighers and other plant transducers produce a very powerful management tool. “To measure is to know”.
For more information on Lodestone Electronics Ltd., please visit:
https://edir.bulk-online.com/profile...lectronics.htm ■