Why Do Laboratories Weigh… Air? The Impact of the Environment on Measurement Results
In a laboratory, the weighing result depends not only on the sample and the balance’s specifications. Environmental conditions also play a role: temperature, pressure, humidity and even CO₂ concentration. When performing very precise measurements, the influence of these factors can no longer be ignored.
Why Does Air Matter?
A sample placed on the weighing pan is surrounded by air, which exerts a buoyant force on it. The magnitude of this force depends, amongst other things, on the density of the air, which varies with temperature, pressure and humidity. Therefore, two measurements of the same sample taken under different conditions may yield slightly different results. The greater the measurement accuracy, the more significant these differences become.
Temperature
Changes in temperature affect both the density of the air and the sample itself, as well as the balance components. A warm or cold sample may also cause convective air movements, which make it difficult to stabilise the reading.
Pressure
Higher pressure means greater air density and, consequently, greater buoyancy. In high-precision measurements, the effect of atmospheric pressure may therefore need to be taken into account.
Humidity and CO₂
Water vapour and carbon dioxide alter the composition and density of the air. In typical measurements, their effect is negligible, but in high-precision metrology, these parameters may also be significant.
How Can Environmental Influences Be Minimised?
A stable temperature, no draughts, proper sample preparation and regular monitoring of environmental conditions are essential for accurate weighing. It is also important to use a suitably selected balance and its functions that support control of the measurement process.
RADWAG Balances – Accuracy Which Takes the Environment Into Account
The smaller the sample mass and the greater the required accuracy, the more important the conditions under which the measurement is performed. That is why RADWAG’s range includes instruments designed for various levels of accuracy – from the 5Y series ultra-microbalances and microbalances, through the 5Y series analytical balances, to the AS X7 analytical balances.
The 5Y series ultra-microbalances and 5Y series microbalances are designed for the most demanding measurements, where even the slightest changes in mass are significant. With such high sensitivity, environmental influences – including air movement, temperature and pressure changes – become particularly significant. The design and features of these balances are intended to facilitate stable, repeatable results even when measurement requirements are exceptionally high.
The 5Y series analytical balances meet the needs of laboratories where high accuracy and thorough control of the weighing process are required. These are solutions for day-to-day research and analytical work, where it is not only the resolution of the balance itself that matters, but also the ability to monitor the conditions under which the measurement is performed.
The AS X7 analytical balances, on the other hand, combine high accuracy, excellent repeatability and design features that minimise the influence of the environment. The series includes models with a readability of 0.01 mg, as well as models with larger weighing ranges. The spacious weighing chamber minimises the impact of air movement on the result, whilst the stable aluminium base ensures the stability of the measuring system.
The AS X7 balances can also be integrated with the THBR 2.0 System – Ambient Conditions Monitoring, which allows for the monitoring of environmental parameters relevant to the weighing process. The balance can therefore not only display the result, but also provide information about the conditions under which that result was obtained.
This is particularly important for the most demanding measurements. The greater the accuracy of the balance, the more difficult it is to consider the measurement result in isolation from the environment. Temperature, humidity, pressure and air properties become part of the entire measurement process, and a suitably selected balance helps to control this process.
