In the packaging industry, the weighing rules are tough, and the standards are even tougher, weighing balances are like the MVPs that keep things running smoothly.
Whether you’re aiming to nail the FDA / Therapeutic Goods Administration (TGA) / Medsafe pharmaceutical requirements or staying sharp with ASTM measurement standards, picking the right balance can be the game-changer between crushing your goals or getting hit with some costly penalties.
This guide’s got everything you need – from different types of weighing balances, how they work, what they’re used for, and a rundown of the pros and cons.
Let’s break it down and get you ready to tackle types of weighing balances.
Load Cell Based Weighing Balances
A load cell-based weighing balance operates by converting weight into an electrical signal.
The weighing pan/platform of load cell weighing balances are connect to a load cell via a mounting assembly. The load cell in turn is connected to a balanced strain gauge.
When the load is placed on the weighing platform the load cell deforms under the load’s weight which changes its resistance.
This change in resistance throws the initially balanced strain gauge off balance. An off balance strain gauge produces electrical voltage whose magnitude is proportional to the weight of the load.
The voltage produced by the strain gauge is typically in the milliVolt range which is not sufficient to run the display. Therefore, an amplifier is used to increase its magnitude.
Next, an Analog-to-Digital Converter (ADC) converts the analogue voltage to digital data.
Then, a microcontroller processes this digital signal to compute the weight, and displays it on the display.
Load cell-based weighing balances are used to measure small and large weights. Ultra sensitive, high precision load cells designed for use in labs can measure weights as small as 1 milligram. These load cells also have a very high precision, typically between 1/3,000 to 1/200,000 divisions.
At the other end of the spectrum, load cells designed for heavy industrial applications, such as those used in construction or mining, can measure extremely large weights—up to thousands of tons. For example, load cells used in truck scales or large industrial cranes can measure weights in the range of 500 tons to over 1,000 tons.
Typical industrial-grade load cells have an accuracy rating of around 0.1% to 0.5% of full scale. For a 1,000-ton load cell, this would mean an accuracy range of ±1 tons to ±5 tons.
Components of Load Cells
Housing: The external casing that shields the inner components from external factors like dust and moisture.
Display: Typically LCDs (Liquid Crystal Displays). Cheaper models have LEDs (Light Emitting Diodes). Some systems use touchscreens or remote wireless displays.
Load Plate/Pan: The surface where the load is placed is typically made of aluminium or tool steel. Specialised weighing balances use stainless steel, titanium, or even Inconel®.
Feet: Adjustable supports at the bottom to level the balance on uneven surfaces.
Connection Ports: Load cells we typically see around us do not have ports. Commercial load cells have one or more of the following connection ports.
- M12 Connector
- DB9 Connector (D-subminiature)
- Binder Connector
- 6-Pin Circular Connector
- RJ45 Connector
- T24 Telemetry Connector
Keypad/Buttons: Expect to see one of the following on almost all load cell weighing balances.
- Membrane Keypads
- Mechanical Buttons
- Touch-Screen Interfaces
- Sealed Rubber Keypads
Draft Shield: A transparent cover used in precision load cell balances to prevent air currents from affecting the measurement.
Torsion Balances
Why do 52% of pharmacies use torsion balance in their practice?
Not only pharmacies, torsion balances are used in legal metrology, physics classrooms, geophysics, material analysis, and chemical laboratories.
The reason is simple—they are precise with small weights. A torsion balance measures a vertically suspended wire’s twisting force (torque). The twisting force can be gravitation, electromagnetic, or magnetic.
The unique part of a torsion balance is that its pivots resist both twisting and stretching, helping the beam return to its horizontal position once the weight is removed.
Some designs use flat ribbons or multiple wire pivots, for more accuracy and stability.
Adjustable collars secure the pivots to the beams. A knob on the collar allows for fine adjustments. Turning the knob left or right eliminates zero error.
Torsion balances have an accuracy between ±0.01% to ±0.1% and their precision typically falls within ±0.1% to ±0.5% of the measured value.
Capacitive Balance
Capacitive balances work on the principle of capacitance, which involves measuring changes in electrical charge. Capacitors used in capacitive balances have two metallic plates ( with dielectric material between the plates.
One plate of the capacitor is connected to the weighing plate via a system of levers and linkages.
When weight is placed on the balance distance between the plates reduces which increases the capacitance or the amount of charge the capacitor can hold. The electronics detect this change in capacitance, convert it into a voltage signal, and then calculate the weight based on that signal.
Capacitive balances offer precision as fine as ±0.001 g and accuracy between ±0.01% to ±0.1%, making them ideal for tasks like chemical analysis and pharmaceutical work. They are also dust and moisture-resistant.
Vibrating String Technology (VST) Balance
The principle behind a Vibrating String Technology (VST) balance is based on the physics of vibrating strings. The frequency at which a string vibrates depends on three properties – tension, length, and mass.
Tension: A tighter string vibrates faster (higher frequency), while a looser string vibrates slower (lower frequency).
Mass or load: When weight is applied, it increases the tension in the string.
In a VST balance, the string is set to vibrate at a known frequency.
When weight is placed on the weighing pan, the string stretches, which increases the tension in the string. As the tension increases, the string vibrates at a higher frequency. The heavier the object, the more the string stretches, causing a greater increase in tension and a corresponding rise in vibration frequency. This change in frequency is then measured to determine the weight of the object.
VST balances offer accuracy between ±0.001% and ±0.01%, with precision that can detect changes as small as ±0.0001 g. They’re commonly used in research labs, material science, and high-precision industrial processes.
Beam Balances
A beam balance measures weight by comparing it to known weights. It has a horizontal beam balanced at a central pivot with trays on each end.
The idea is simple: place the object on one tray and known weights on the other. The beam will tilt towards the heavier side. When the beam levels out, the object’s weight equals the combined weight on the opposite side.
A variation is the triple beam balance, which uses three beams with sliding weights. Each beam has different increments—usually 1 gram, 10 grams, and 100 grams.
To use it, the object is placed on the pan and weights are moved along the beams until the balance is level.
The total weight is the sum of the positions of the weights. This design gives precise measurements.
Triple beam balances are commonly used in labs, commercial establishments, and factories.
Quartz Crystal Microbalance (QCM)
A Quartz Crystal Microbalance (QCM) measures minute weight changes by utilising a quartz crystal that vibrates at a precise frequency when subjected to an electric current. When material is deposited onto the crystal’s surface, the additional weight causes a decrease in its vibration frequency. The balance detects this frequency shift and accurately calculates the weight of the added material.
This method boasts an exceptional accuracy, typically within ±0.001% to ±0.01%, and offers precision capable of detecting mass changes as small as ±0.1 nanograms. Due to its sensitivity, QCM is employed for analysing small quantities of material in chemical analysis, thin film deposition monitoring, and biosensing applications, with the final measurement conveniently displayed for easy interpretation.
Piezoelectric Balance
A Piezoelectric Balance uses piezoelectric crystals to measure weight. Piezoelectric crystal that generates an electric charge when pressed – a phenomenon known as piezoelectricity.
This crystal converts mechanical energy from the applied pressure into electrical energy. When weight is placed on the balance, it presses on the crystal, producing a charge proportional to the force applied.
Piezoelectric balances have an accuracy of ±0.003% to ±0.2% and can detect changes as small as a few micrograms. They are used in labs for tasks like pharmaceutical research, material science, and chemical analysis.
Spring Balance
A spring balance measures weight using a spring fixed at one end with a hook on the other. When an object is hung from the hook, gravity stretches the spring, and the amount of stretch corresponds to the object’s weight.
This balance works on the principle of Hooke’s Law, which states that the stretch of a spring is proportional to the applied force, as long as the spring’s elastic limit is not exceeded.
The scale on the balance is typically calibrated in Newtons or grams, so as the spring stretches, the pointer moves along marked units, showing the weight. Spring balances are often used in classrooms.
Accuracy ranges from ±1% to ±2%, and precision can vary between ±1% and ±5%, depending on the device’s quality. Environmental factors like temperature, humidity, and wear can also affect performance.
Electromagnetic Force Restoration (EFR)
An Electromagnetic Force Restoration (EFR) balance measures weight by using a magnet and coil system. When an object is placed on the pan, it exerts a force. The balance counteracts this force by generating an equal electromagnetic force. The balance measures the electric current required to maintain this equilibrium and converts it into the object’s weight, which is displayed.
EFR balances are capable of resolutions as fine as 0.1 micrograms (µg) and can measure weights from micrograms to 120 kilograms. They provide repeatability within ±0.01 mg, ensuring consistent measurements. To maintain accuracy in difficult environments, features like Active Vibration Compensation (AVC), temperature compensation, and anti-static measures are used.
Conclusion
Weighing balances are essential tools in various industries and scientific fields, each type offering unique advantages and specific applications. The right choice of balance enhances efficiency, accuracy, and reliability in measurement tasks, driving better quality control and operational efficiency.
FAQs
Why is regular calibration important for weighing balances?
Regular calibration ensures that the weighing balance maintains its accuracy and precision over time. Environmental factors, wear and tear, and usage can affect the balance’s performance. Calibration adjusts the balance to correct any deviations, ensuring reliable measurements.
Can equal arm balances be used for precise scientific research?
Equal arm balances are generally not suitable for highly precise scientific research due to their limited accuracy. They are more commonly used in educational settings and for basic weight measurements where extreme precision is not required.
How does a microbalance differ from other types of balances?
Microbalances are designed for the highest precision in measuring extremely small masses, often down to micrograms. They feature ultra-sensitive sensors, advanced calibration systems, and protective enclosures to ensure accurate measurements, making them ideal for advanced scientific research, nanotechnology, and biochemistry.
What factors should be considered when choosing a weighing balance for a laboratory?
When choosing a weighing balance for a laboratory, consider the required accuracy and precision, capacity, environmental conditions, frequency of use, and specific applications. Additional features like digital displays, calibration mechanisms, and protective enclosures may also be important depending on the intended use.