Digital scales are precision instruments. With proper care and handling, they will provide years of service. End users should be aware of the factors which may affect the accuracy, precision, usability, and reliability of their scales.
Unless explicitly stated, many digital scales are designed for indoor use only. They work best when operated and stored indoors with standard room temperature and relative humidity. Before first using a digital scale, it is necessary to allow it a minimum of an hour, or ideally, 12 hours, to acclimate to the local environment and to reach its optimal parameters. Maintain the local temperature and relative humidity within the human’s comfort zone. Avoid exposure of the instrument to rapid temperature changes, direct sunlight, and strong air flows. Keep a digital scale away from a field of magnetic, static electricity, or electromagnetic disturbance. Avoid using it near wireless devices, such as WiFi access points and cordless phones, or its readout may become unstable.
Tech Note
When temperatures increase, resistance in the wires increases. It can cause the voltage to drop. The scale controller may display a result different from the load cell output. Also, condensation or moisture can occasionally build up on the load cell sensor. It will affect electrical outputs and cause interference in the signals transferred from the load cell to the circuit board and the display.
Power Source
A digital scale is sensitive to power fluctuation. It must use power supplied by appropriate batteries or an AC power adapter. Always verify the electrical rating of a power adapter before connecting it to a scale. In an area experiencing lighting strikes or unstable electrical power supply, connect its power adapter to a surge protector, or only use quality batteries to power the scale. If not to use a scale for a long time, disconnect its power adapter and remove all batteries from its battery compartment.
Tech Note
The electronic components, load cell, printed circuit board assembly, and LCD panel inside a digital scale are sensitive to unstable power supply. Low battery power or faulty AC power adapter may cause display readout fluctuation and inaccuracy. If in doubt, only use a fresh set of quality batteries to power and test a scale.
Load Cell Transducer
One or more load cells and multiple attached strain gauges form the heart of a scale. They work together as the transducer to convert mechanical energy, such as tensile and compressive forces, into electrical signals. Similar to a spring element, each load cell’s elasticity suffers from daily usage over time. It is normal wear and tear.
Every load cell has its maximum capacity. If a load cell is overloaded, it will permanently deform and lose some degrees of elasticity. End users shall pay close attention to the specifications of a scale. Do not overload it, and avoid shock loading. After weighing operations, remove everything from the weighing pan. When a scale is not in use, its pan should be empty. Regular testing and re-calibration jobs are necessary to confirm the accuracy and precision of a scale.
Tech Note
A standard metal load cell is sturdy but also minimally elastic. It works as a spring element. It slightly deforms when a force is applied. It returns to its original shape when the force is released.
A strain gauge includes parallel fine wires, flexible backing, and encapsulation. Bonding multiple strain gauges to the metal surface of a load cell body can monitor its deformation. Once the load cell deforms, the strain gauges will change their shape and resistance. The alternation to resistance in the strain gauges is measurable as voltage. It is proportional to the amount of the force applied to the load cell. With proper calculation and conversion, the amount of force, such as weight, can be displayed.
Calibration
Most digital scales are factory-calibrated and ready to use in many non-critical cases. However, packages in transit, temperature changes, geographic gravity variations, altitude changes, and even daily usage may affect their calibration. End users shall regularly verify the accuracy of a scale and record the results. A scale will require re-calibration if its accuracy is beyond a preset permissible tolerance.
To re-calibrate a scale, end users may consult its user manual for procedure. Note the required calibration weights. Use appropriate calibration weights classified by a metrology standards organization such as International Organization of Legal Metrology (OIML). Avoid non-standard weights: fitness dumbbells, kettle bells, or plates.
Tech Note
OIML Calibration Weight Class Class E1: The highest accuracy class for calibrating E2 weights and lower. Class E2: Intended for calibrating F1 weights and lower. Suitable for calibrating high-precision analytical balances with a readability as low as 0.01-0.1mg. Class F1: Intended for calibrating F2 weights and lower. Suitable for calibrating high-precision top loading balances with a readability as low as 1-10mg. Class F2: Intended for calibrating M1 weights and lower. Suitable for calibrating moderate precision analytical balances and use in high-value commercial transactions such as precious metals and stones. Class M1, M2, M3: Economical weights for general laboratory, industrial, business, technical, and educational uses.
Case and Weigh Pan
Impact-resistant Acrylonitrile Butadiene Styrene (ABS) case and stainless steel weigh pan protect a digital scale’s internal electronic components under normal use conditions. However, excessive trauma and careless behavior in handling a scale will damage it.
Protect a digital scale from dropping, shocking, and other abuses. To avoid shock loading, carefully place items centrally on the weighing pan. Keep the load balanced and centered. Preserve its finish by wiping only with a slightly dampened soft cloth. Do not use solvents, harsh chemicals, abrasive and corrosive cleaning agents.
LCD Display
Backlit 7-segment LCD is a standard technology for enhancing the contrast of a scale’s display. When powered by batteries, the display will turn off automatically after approximately 5 minutes of inactivity to save some battery life. When some applications require a scale turned on for a longer period of time, use a compatible AC-DC adapter to power it without triggering its auto-sleep function. Beware of its DC output rating before connecting an AC adapter to a scale. Note that some backlit LCD panels are not for 24/7/365 continuous operation. When not to us a scale for a while, such as overnight, it is better to turn it off to prolong its service life and save some energy for the planet.
