Environmental Effects on High Precision Weighing Devices
There are a number of environmental factors to consider when installing a high-precision scale. The location of scale can affect its ability to produce accurate results. The below article is an excerpt from the METTLER TOLEDO Right Way to Weigh brochure. While it was written as a guide for balances, it contains a lot of great advice for the installation of high-precision bench scales and counting scales.
Location of the Balance
The precision and reproducibility of weighing results is closely associated with the location of the balance. To ensure that your balance can work under the best conditions, please observe the following guidelines:
- Stable (lab bench, lab table, or stone bench). Your weighing bench should not sag when work is carried out on it and should transfer as few vibrations as possible.
- Antimagnetic (no steel plate).
- Protected against electrostatic charges (no plastic or glass).
- Wall or floor installation. The weighing bench should be fixed either to the floor or to the wall. Mounting the bench on both places at once transfers vibrations from the wall and floor.
- Reserved for the balance.
The place of installation and the weighing bench must both be stable enough for the balance display to not change when someone leans on the table or steps up to the weighing station. Do not use soft pads underneath, such as writing mats. It is better to position the balance directly over the legs of the bench since the area is subject to the fewest vibrations.
Work room
- Vibration-free
- Free from drafts
Place the weighing bench in a corner of the room. These are the most vibration-free areas of a building. Ideally, the room should be accessed through a sliding door to reduce the influence of door movements.
Temperature
- Keep the temperature of the room as constant as possible. Weighing results are influenced by temperature! (Typical drift: 1-2 ppm/°C).
- Do not weigh near radiators or windows.
METTLER TOLEDO balances with “FACT” (fully automatic motorized self-calibration) can compensate for virtually all the remaining temperature drift. For this reason, “FACT” should always be switched on.
Atmospheric humidity
- Ideally, the relative humidity (% RH) should be between 45 and 60 %. Balances should never be operated above or below the measuring range of 20 to 80 % RH. Constant monitoring is advisable with micro balances. Changes should be corrected whenever possible.
Light
- If possible, place the balance on a window-free wall. Direct sunlight (heat) will influence the weighing result.
- Place the balance a significant distance from lighting fixtures to avoid heat radiation. This especially applies to light bulbs. Use fluorescent tubes.
Air
- Do not place the balance in the airflow of air conditioners or devices with ventilators, such as computers or large laboratory devices.
- Place the balance at a sufficient distance from any radiators. In addition to the potential temperature drift, strong currents of air could interfere with the operation of the balance.
- Do not place the balance next to a door.
- Avoid places with high traffic.
Passersby will usually create a draft at the weighing location.
Click here to read the whole brochure:
