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Load Cell Calibration for Universal Testing Machines
Calibration Support across the USA and North America
Galdabini's universal testing machine load cells can be verified by any professional load cell calibrator. The calibration process involves using a secondary reference standard load cell, often called the "master". Master load cells are 10x more precise and are available from popular load cell manufacturer's such as Interface Force in the US and HBM of Germany.
All Galdabini load cells are calibrated in Galdabini's accredited calibration laboratory at their HQ near Milan, Italy. The image to the right shows Galdabini's 100 ton dead-weight force calibration system, one of the largest in the world. Dead-weight calibration systems are certified by governmental institutions such as NIST and are required for calibrating reference standard load cells.
How to Verify the Load Cell Calibration on a Universal Testing Machine
Most ISO/IEC 17025 based calibration sessions only require verification of the calibration of the load cell. This service must be done on-site and is most economically performed through a local calibrator. Modern load cells will maintain their calibration unless they are damaged due to overloading, extensive use, moisture, or electromagnetic interference.
The master load cell is rigidly mounted between the crosshead and the base of the machine using adapters. The setup is slightly different when calibrating in either tensile or compression as can be seen in the below pictures. UGC offers all adapters and platens necessary for the calibration process. If the machine is suspected to be out of alignment, a universal joint or cardan adapter is used. The master load cell is connected to a digital readout so that the operator can compare the force measurement of the machine's load cell to the master.
The machine is set to calibration mode where the crosshead position is controlled via a closed feedback loop from the load cell. This is often called load control vs. the usual position control. The machine is then set at varying intervals within the load cell range. For instance, a 10kN load cell may be tested at 500N, 1kN, 2kN, 5kN, and 10kN. Usually 10 points is most common. The master's readout is then compared to the machine's load cell to check for the amount of deviation. If the deviation is out of spec, the internal values of the load cell must be re-calibrated using either a shunt or direct force calibration.
Shunt Calibration vs. Direct Force Calibration
If the load cell is deemed to be out of spec, it needs to be re-calibrated. Load cells can be calibrated in two ways. The first is a shunt calibration which requires sending an electrical voltage of known value to the load cell's strain gauges. Modern load cells contain 4 strain gauges in a Wheatstone Bridge configuration. Shunt calibration can be thought of as a sort of electrical reset. The value of the electrical signal is specified on the load cell's original documentation from the manufacturer. Shunt calibration is a relatively quick process and can be done on-site. The electrical signal for the shunt calibration is sent from a small, usually handheld, electrical device that the calibration technician will have.
If the shunt calibration does not work, usually due to damage to the load cell, a direct force calibration must be performed. Direct force calibration requires sending the load cell back to an accredited calibration facility. For US based machines, Universal Grip recommends sending the load cell to Interface Force in Scottsdale AZ. For more information on load cell repair and re-calibration, please click here. Interface can repair and re-calibrate Galdabini load cells and load cells from most any manufacturer. Turn around time is usually 5-7 business days with a rush option available.
List of Calibrators by Region - Ask us for a reference
New England (MA, CT, ME, NH, RI, VT)
Mid-Atlantic (DE, NJ, NY, PA)
East North Central (IL, IN, MI, OH, WI)
West North Central (IA, KS, MN, MO, NE, ND, SD)
South Atlantic (FL, GA, MD, NC, SC, VA, DC, WV)
East South Central (AL, KY, MS, TN)
West South Central (AK, LA, OK, TX)
Mountain West (AZ, CO, ID, MT, NV, NM, UT, WY)
West Coast (CA, OR, WA)
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