Does anybody know the calibration procedure of Coal feeder load cell and what are the equipments for calibration system? I'm just newly hired as I&C Engineer and my Boss assigned me to make calibration procedure of coal feeder load cell.
To calibrate or verify the calibration and accuracy of any process weighing system requires either a portable load-cell calibration kit complete with a digital display attached or a remote hand held wireless display unit or a set of assizes (weights checked and stamped by department of commerce) weights. The weights must be able to go to at least 80% of the capacity of the installed load cell. The type of calibration and kit will depend on your application and if it is possible to remove the installed load cells or not.
Another easy and relative inexpensive way it can be done is to use water bags, because 1 liter of H2O = 1 Kg in weight so 1000 liters of H2O is equal to 1000Kg and therefore 1Ton in weight.
We sometimes use these water bags to do a quick load calibration verification check on the cranes. You might be able adopt this idea and use a similar setup by hanging the bags of the feeder at various points where the load cells are installed or just use one bag and change from load cell to load cell to make sure all of them give the same reading. This will have the benefit that you can verify the accuracy of the one load cell with the reading of another, since if all of them read the same the chances are 99,99% that they are ok, not damaged and still accurate.
Remember to take into consideration the weight of the bag itself. The total weight of the feeder on the load cells displayed originally during installation, would have been the total “Cross” weight of the system, the weight of the feeder would have been “Tared” out in order to give a zero indication with no product load on it. The coal going through the feeder is the “Net” weight and that is displayed on the weighing system display. You can do the same with the bags. The bag is the “Tara” weight and the water itself will be the “Net” weight. The weight of the bag can be “Tared’ out so that you will have a zero indication before you start filling the bag/bags. You then fill the bags with a known amount of water and get a accurate simulated weight which you then can compare with what your weight display reads. Another benefit would be that you would not have to dismantle everything and remove the load cells.
Some companies do not believe the accuracy requirements justify the expense of the kits or weights, so they just do some measurement checks on the load cell and leave it at that, so if you only want to do that on each load cell, here’s how:
The standard output of most load cells is 2mV/V. Most use a wheat stone bridge and have a max output of +/- 20mV @ 10V excitation. This means that if you apply 10V at the excitation pins, and put full weight on the load cell, it will give 2mv X 10V = 20mv output at the output pins, or if you supply the load cell with 5 V at full load you will get only a 10 mV output.
Depending on how important this accuracy is to your company, you can tell your boss he needs to buy you some load cell test rigs, weights or water bags fist if he wants you to do a accurate calibration test. For now you can only give him the mV readings as proof that the load cells are still in good working order keeping in mind that these readings is not a alternative to a calibration verification check.
