Scale Calibration

What is scale calibration?
Calibration of a scale is a procedure in which a technician uses known weight certified by the States of Missouri, Kansas, Iowa and Nebraska Bureau of Weights and Measures, to adjust the response of a mechanical or electronic weighing system to the following tests; The indicator must show zero when there is no weight on scale. When a known weight is applied the indicator must display the exact amount of applied weight. When weight is applied or removed incrementally the scale must display weight equal to that on the scale.

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Why is calibration needed?
All scales need to be calibrated when first placed into service to insure accurate operation. Any scale will, in time, drift away from its original calibration. Wear of mechanical components, age and degree of use all contribute to calibration drift. The many require that any scale used to sell a commodity or service must be inspected and certified as to it’s accuracy.

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How often must I calibrate?
There are several factors to consider when deciding on frequency of scale calibration testing is scale operating in a hostile environment? How much is this equipment being used, one two, three shifts, only several times a week? Are there Quality Control parameters which must be maintained such as U.S. Government or ISO 9000? How long can your company afford to allow scale equipment to operate with a possible error in weight reading?

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How can I set up my equipment for regular calibration?
Ace Scale Company will assist in setting up your custom program by taking into consideration all of the above questions. It is recommended that scales be calibrated quarterly, however, many times a program is initiated that begins with a high frequency of testing and then is adjusted to the equipment needs. Ace Scale Company will perform the tests as prescribed in the calibration and test procedure statement.

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Calibration & Test Procedures

Cleaning
Display: Clean the display and note any problems (water on a non-washdown indicator, etc) on the calibration report. Items such as paint or other chemicals that cannot be removed without harsh cleaners should be left on the equipment. Platform: The scale deck should be wiped free of foreign materials and checked for obstructions. Check under and around the platform for foreign materials. Remove any items that will adversely effect weighing accuracy. Pit type scales should be checked for clearance around the pit walls and obstructions removed if necessary. An additional charge will be made for removing the scale from the pit for pit cleaning. Mechanical scales should be checked for freedom of movement in all directions. Where possible, remove the platform and clean the lever system. Ramps: Check the general structural appearance of the ramps and insure that they are securely fastened. The ramp should not move into the scale when loading or unloading.

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Inspection
Marking: All scales should be properly marked with the capacity and count by on the display panel or the serial tag. "Legal for trade" scales must be properly marked in accordance with Handbook 44 requirements. Re-mark the scale with permanent placards (marking systems which press numbers into plastic tape are not acceptable to the state Dept of Ag). Load Cells: Proper marking is required if the scale is "legal for trade". These marking plates are especially important when placing the scale in service for the first time but should remain with the load cell at all times. Signal Cable: Inspect the signal cable connecting the scale platform to the indicator for cuts and abrasions. Also, check any connectors for damage or pulled wires. Cables with splices should be brought to the owner’s attention and replacement recommended. Power Test: Visually inspect wall receptacle for physical damage and test polarity if in doubt. Look around the area to determine if any machines, which can produce line noise, are on the same circuit. Battery powered scales should be checked for proper operation on battery. Scales that have internal battery backup of memory should be unplugged for 1 minute to determine if the internal battery has sufficient charge to maintain memory.
Over Load Stops: Visually inspect the over load stops for proper clearance. Small bench scales should be loaded to capacity to determine if the stops have sufficient clearance and with capacity weights on the scale, gently push the platform to insure that the stops are engaged with very little movement required. Adjust as necessary.

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Testing
Overview: Test procedures will be adhered to, unless other test procedures are requested by the customer. All tests should be completed and the initial error properly marked before corrections are started (including cleaning). If the equipment is not operable upon arrival and the repair changed the calibration, indicate so in the initial error section ("not completed – equipment inoperable"). All errors will be indicated in divisions, not graduations. Review the instruction page for completing the Calibration Report before beginning work.

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