Datexel balances the plant.


A mining company could not balance its through put into and out of the reduction plant. Although the flow meters, density meters and belt scales were calibrated weekly, the amount of material coming in to the plant was 15-30 % higher than the output which was a single flow meter and density meter giving mass flow.

Whilst a Datexel Engineer was visiting the plant a Technician told him of the problem and asked if he knew someone that could supply more accurate Instrumentation. As the Datexel Engineer had a lot of experience in Instrumentation he knew it was not possible for the equipment to be out of calibration that much.

Armed with a loop calibrator and a multi meter, the engineer solved the problem in less than 30 minutes. The flow meter suppliers and belt scale company had been to the plant numerous times but could not solve the problem. The plant technician was spending up to eight hours a day trying to solving the problem.


There were two problems:

Problem 1

The 4-20mA from the density meter was connected correctly in series with a mass flow calculator, an indicator and a recorder. Each time the 4-20mA was measured it was measured with the loop removed, so it was not in series with the loop. It was measured by the Datexel Engineer in series and the density meter was forced to emit 20mA. It was found that the density output dropped to below 18mA. The simple solution was to fit a DATEXEL DAT4631D splitter. The density meter fed the 4-20mA to the splitter. The splitter then provided 2 outputs, both with an impedance of 750 Ohms. To improve the integrity of the system a DAT4631D was used that also provided isolation between the input, the power supply, and the two independent outputs.

Problem 2

As the distance from the belt scale and the control room was a great distance the integration was done in the control room and not in the belt scale. As there were two separate earths being used on this loop i.e. the ground in the control room and the ground on the plant, there was a potential ground difference and a ground loop was present. A 20 mA was forced on the belt scale and only 14.5 was measured in the control room. A DAT511 was installed in the loop and it improved to 19mA. As the DAT511 is a loop powered isolatation unit is was thought the impedance of the long cable and the impedance of the integrator caused the load to be too high. The DAT511 was replaced with a 4 wire isolator DAT4135. This corrected the reading to 20mA.
All the loops had either splitters, if there was an impedance problem, and loop powered isolators if the impedance wasn’t a problem, and the plant figures balanced.

The Site Engineer and the Plant Manager were very happy as it was the first time in two years that the figures actually balanced.

The experience of the Datexel Engineer improved the running of the plant and increased the accuracy of their measurement. Saving the company many dollars in daily calibration. The company now calibrates once a month. Also the Technician did not have to buy more accurate Instrumentation.