Trial and Error Method

TM 5-3895-374-24-1 Calibration with Weights Note You must set the following Parameters before initially adjusting the Dead Load or Span. [11] [SELECT] Set Load Cell Full Scale Output. This parameter represents the output of the load cell, in millivolts, at maximum scale capacity This entry acts as a coarse span or span range adjustment for the indicator matching it with the working range of the load cell. This value must be set accurately to achieve the rated performance from the indicator. You may use one of two methods for determining the value of this parameter - the formula or the trial and error method Formula: The formula for determining the output of the load cell is as follows: Amount of Load Cell Used Rated Millivolt Output Load Cell Capacity of Load Cell at Capacity e.g. Using a 1,000 lb. Load Cell of 3 mv/v range and estimating you are using 40% of the cell capacity, you would obtain the formula 400 Lbs. 1000 Lbs. X 3 x 9= 10.8 Round this off the nearest integer number, i.e. 11, and enter this value, e.g. press [1] [1] (ENTER]. Note: Only integer numbers from 8 to 35 may be entered for this value. Trial and Error Method In this method you will try various values for this parameter and see what the resultant scale readings are 1. First make sure that the scale and load cells are wired up correctly. Then press the (WEIGHTS/COUNTS) key. The flashing ’[’ in the leftmost display digit will be replaced by a flashing ’A’ and a number should appear. The indicator is now in the Counts mode. Make sure the scale is clear of weight and note the value of this number. This number represents the internal raw counts. If a number does not appear and the display shows ’uuuuuu’ check the Troubleshooting Section VI. For example Scale clear of weight - internal raw counts are 3431 2. Apply a known weight on the scale that represents a fraction of scale capacity and note the change in the reading. For example Scale capacity is 5,000 lbs. Apply 1,000 lbs. (1/5 of capacity) - internal raw counts are 11223. Change in reading is 11223 - 3431 = 7782 The indicator has 60,000 internal raw counts available and, for maximum performance, you want the internal raw counts to be between 50.000 and 60,000 at scale capacity Therefore, at 1/5th capacity (above example), the change in the internal raw counts should be between 10,000 and 12,000 counts. Checking the current value for Parameter 11: [11] [SELECT] --> displayed value = ’14’ You must change this value until the above procedure gives you a change in internal raw counts of between 10,000 and 12,000 counts. In this example you must decrease the value of Parameter 11. Note: Decrease Parameter 11 to increase the change in counts. Increase Parameter 11 to decrease the change in counts. For example: Press [11] [SELECT] --> displayed value = ’14’ Change to ’12’, press [1] [2] (ENTER). (page 3-64) X X