The first definition of mass, the amount of matter contained in an object, came about during the Scientific Revolution at the end of the 1700’s and has come far since then. Long before that, weight, the measure of the force exerted on an object due to the acceleration of gravity, was measured in seeds or grains of rice. The difference between mass and weight is mass is the amount of matter and weight is how the force of gravity acts upon that mass. Thanks to modern technology, we have many easier and more accurate ways to measure weight and mass. For centuries, balances have allowed us to measure mass and weigh objects and they have only gotten better through history. Precision balances can measure mass down to the milligram and sometimes further. How A Precision Balance Measures Put simply, a balance tries to equalize the force created by the object and the resistance force. In the case of a precision balance, the resistance force is created using a coil of wire wrapped around a magnetized spring. According to LabMed, magnetic force restoration is the system that allows mass to be measured in precision balances. A typical mechanism includes a coil of wire suspended by magnetization. A sensor detects the position of the coil and sends feedback to an electronic amplifier which adjusts the flow of the current allowing the coil to stay at the reference point. The machine measures the current, which is proportional to the force exerted by the object you are measuring, allowing measurement of mass. Sensitivity and movement With great precision, comes great sensitivity. The inner workings of a precision balance, listed above, are a delicate system that depends on stability and consistency to measure accurately. According to Lab Manager, changes in temperature, humidity, and air pressure all affect balances accuracy but temperature changes are by far the most serious because they occur everywhere and at all times. This is why temperature-controlled environments are crucial for not only precision balances, but for sensitive instruments of all forms. Drafts of air, flexible table surfaces, and moving or shaking floors also pose a threat to precision balances calibration. Because of this, precision balances are often kept on the lowest allowable floor of a laboratory and recommended to be placed on granite or other nonflexible tabletops. The image above is the Kibble balance located at NIST in Gaithersburg, Maryland. Why Moving and Shipping For Calibration Is A Bad Idea These machines are designed to be sensitive to the most minimal of movement. Perhaps the biggest risk in moving or shipping your precision balance for calibration is not the trip to the facility but the trip back. Do you really think putting a FRAGILE label on the package will make a difference in how it is handled in transit? If the balance is jostled too heavily in transit, it will be fixed upon arrival with the recalibration. But, in transit back to your facility, any jostling, temperature, humidity or air pressure change will undo the calibration that was just done. Calibration of precision balances in-house is the best route to take to continue with accurate and well-maintained machines. Calibration without movement Properly spaced intervals between calibration are crucial to precise and accurate results. Calibration cycles can be determined by examining historical data of each particular machine or checking with your laboratories accreditation standards. Many laboratories have specific calibration procedures to follow, ensuring repeat accuracy and abiding by accreditation standards. Following your laboratory calibration standards will allow you to successfully calibrate your machine without the risks involved with the movement. Conclusion: Do not ship your precision balance for calibration. Schedule an onsite calibration.
