Bulk Equipment, Sensors

CST’s belt weigher calibration at a glance

Ian Burrell, managing director of Control Systems Technology (CST), explains how the company’s belt scale electronics use a patented feature to make calibration easy.

Ian Burrell, managing director of Control Systems Technology (CST), explains how the company’s belt scale electronics use a patented feature to make calibration easy.

The calibration status of many belt weighers can be a complete mystery to the owner. There is little understanding of the numbers inside the ‘black box’, and on many of the various types of equipment installed at customer sites, there is no transparency about what’s going on inside.  

It’s just not clear what the numbers mean on most equipment, but the CST system makes all the inside calculations visible.

To assist with the task of belt weigher maintenance and to make it easier to understand, the CST system includes a patented calibration dashboard that shows the status of the calibrated sub-systems of each belt scale.

Belt scale zero: Is the zero OK and has it changed much? The belt scale zero area is a button to active the zero function, but it also tells how much the zero has moved since the last manually activated zero, in this case -0.04 per cent, zero tracking is OK, and was last completed 5/10/23. All is well with the zero.

Belt scale span: The span is the number which turns the analog to digital converter (ADC) number into engineering units, in this case kg. It’s the fundamental calibration constant for the belt weigher. Our load cells come with a certified output calibration in mV/V and we convert this to an expected ideal span number. The Belt Scale Button colour indicates agreement between the theoretical ideal span number and the actual number achieved on site with calibration masses. This ‘traffic light’ helps avoid mistakes on site.

Weigh length: This is the weight sensitive length of the weigh frame and is based on a site measurement. To avoid mistakes on site, the measure length is compared with the idler spacing and number of weigh idlers. The green ‘button’ indicates that all is well.

Tachometer: The tachometer is calibrated by finding out how many tachometer pulses there are in a measure length of conveyor belt. This is another very important calibration number. Any error in this number causes an equal error in the belt scale output. The CST system checks the tacho pulses per revolution against the tacho pulley diameter to work out a theoretical tachometer calibration number. By comparing the theoretical and the actual, we can validate the tachometer calibration. The tachometer turning radius is ‘inside’ the conveyor belt, and the screen shot above shows that the belt factor is 54 per cent, which means that the radius of turning is at about the middle of the belt, which is a valid result and so the Tachometer button is green.

Live load: Sometimes it is necessary to adjust the calibration of the belt weigher to account for belt affects and this is most often as a result of comparison with an accurate live load material test. With the CST system, full transparency. Any adjustment is visible in the live load dashboard window. There is no need to fudge weigh frame, tachometer, or weigh length calibration.

Maintenance: When was the belt weigher last checked for good alignment. This can be seen at a glance from the maintenance button area on the calibration dashboard.

CST strives to build the best possible belt weighing systems using the latest technology. 

The dashboard screen above can be viewed remotely via the internet for customers which wish to be connected. The connection is actually via a secure server and two different VPN networks to make doubly sure about security. The remote interface is the best way to provide immediate support for remote sites whether they be in the Pilbara or in South America.

With 40 years of experience in the belt weighing industry, CST is fully committed to the ongoing support of our many existing customers and is pushing forward with new innovative technology. 

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