The weighing process is the heart of any manufacturing application. Whether you’re measuring level or inventory, batch weighing, or monitoring flow rates, there are several best practices that should be followed to obtain accurate results.
Which weighing method is right for you depends on your precision requirements and the characteristics of your substances. Weighing by Difference excels in contamination control and accuracy, while Direct Weighing offers speed and convenience for scenarios where precise measurement is not critical.
Weighing by weight
Weighing is the action of measuring how heavy something is, or its mass. Mass is the amount of heaviness an object has, and is defined as an object’s acceleration times gravity. Weighing is done with a scale or balance.
When weighing by weight it is important that the balance be correctly zeroed (as shown in the image above) by taring. It is also important that a clean piece of weighing paper be placed on the balance pan before adding the sample. This will prevent the sample from sticking to the weighing paper after the reading is recorded and producing an error.
Using the weighed sample, the tared and blank pieces of weighing paper can be subtracted to determine the sample’s mass. This is a method known as “weighing by difference.” This type of weighing should be used only on top loading balances and never on analytical balances since the fine sensitivity of an analytical balance can produce errors that cannot be corrected by this technique.
Weighing by volume
Weighing by volume is used for measuring liquid ingredients. It uses a digital scale and a set of measuring tools to determine the amount of an ingredient by its capacity. To weigh by volume, you must first select the unit of measurement on your scale. To do this, place a bowl on the scale and click the “tare” button. This zeroes the scale so that the contents of the bowl will not be counted in your measurement.
Besides hydrostatic weighing, double-weighing in air is another method to measure the volumes or densities of weights. This method differs from the hydrostatic one because both weights are exposed to air, and different air densities can be simulated by means of pressure control technology. This enables both volume determination and mass comparisons to be performed simultaneously. This method is also more convenient than the hydrostatic method because it does not require immersing a stainless-steel reference weight in water, which may cause corrosion or surface contamination.
Weighing by mass
It’s easy to confuse the terms weight and mass, but there is a difference. Mass is a measurement of the matter that an object contains (think “how much stuff you have”) and is measured in kilograms or grams. An object’s weight changes based on its location in relation to the gravitational force acting on it: an object will weigh less on Mars, more on Saturn, and nothing at all in space.
The easiest way to weigh by mass is with a beam balance scale, like the old-fashioned doctor-style ones with a tilting beam and sliding weight. The unknown masses are placed on the pans, and the known masses are added until the balance indicates equality. You can also calculate the mass of a substance by multiplying its volume and density. Newton’s second law of motion states that force equals mass times acceleration: F = m / a. The resulting formula is usually written as F = ma, but it’s often easier to remember the simpler equation: mass equals a force divided by its acceleration.
Weighing by difference
Weighing by difference is a method for accurately measuring mass. It involves weighing the empty container to obtain its tare weight, then adding or removing the substance to measure its final weight. The initial and final weights are then calculated to determine the chemical’s mass. This technique minimizes errors during transfers and is critical for quantitative analyses.
Unlike volume measurements, weighing by difference is not affected by the shape of the vessel or ingredients that foam, settle unevenly, or have different dielectric constants. Also, it is not susceptible to contamination issues such as bridging and rat holing.
Process weighing systems automate filling and dispensing processes to increase consistency and streamline operations. They can be integrated with a programmable logic controller to capture loss in weight data for real-time process control. HBK offers a range of process weighing technologies, including continuous level and inventory measurement, bag or drum filling and dispensing, batch blending, and silo discharge by weight or rate. These systems help reduce costs, enhance production outcomes, and ensure regulatory compliance.