Although shunt calibration is certainly not a replacement for standard force calibration, there may be times that it can be a convenient method of calibrating strain gauge load cells. Obviously, strain gauge load cells are passive, and causing an intentional imbalance in the “bridge circuit” would be an effective method of checking system gain or span. The electrical imbalance that is generated would mimic the “bridge imbalance” and then the system gain can be adjusted afterward.
While most load cells are strain gauge, there are five different types of load cells available for testing and measurement. Hydraulic load cells can function under extremely cold testing conditions, down to -75 degrees Fahrenheit. Diaphragm, spool, and ring type load cells are also used in addition to hydraulic and strain gauge load cells.
In general, the conversion of force for testing and recalibration purposes is a process that comprises two stages: the force affects — “deforms” — strain gauge load cells, and then the load cells measure that strain in terms of ohms, or electrical resistance. Strain gauge load cells have been widely used for more than four decades, but load cells are generally classified by several criteria.
Load cell output may be electric, pneumatic, or hydraulic, and detect weight either by compression or tension. If the detection mechanism relies upon compression, then the output will measure the force pushing inward along an axis. Shear load cells detect weight through tension, or the force pushing outward or pulling apart, also along an axis.
As non-invasive load measuring and scanning products continue to evolve, the integration of load cell testing and measurement services into existing technology remains an important part of any manufacturing or quality control process. Load cells can actually work in a range of temperatures from -400 degrees Fahrenheit to more than 450 degrees Fahrenheit. Load cells are routinely integrated into systems with measurement services designed to test weight: they are non-invasive, offer accurate load measurement metrics, and can test accurately between 0.03% and 1%, assuming proper installation and calibration.
Industry standards do require recalibration to be performed every two years or less, and if there is heavy wear and strain on the equipment — more than 1% — measurement services and recalibration must occur more frequently. Accurate data is something that is absolutely necessary, and although shunt calibration may just be used occasionally, it will never replace standardized calibration routines.