A&D Weighing has shared their pro tips and solutions when dealing with microbalances. This will be a 3 part series, read on for tips 1 thru 3.
The micro balance is an extremely sensitive device. Its scale interval of 1μg (microgram) is equivalent to 1/1,000,000 of the weight of a paper clip (about 1g). Its resolution can reach as high as 1/22,000,000, as with the BM-20 microbalance.
With such high sensitivity, it should be no surprise that even the slightest disturbances caused by the set-up environment or the way the user interacts with the microbalance can significantly affect measurement stability.
Tip #1: Avoid or isolate all possible sources of vibrations even when you cannot actually feel them.
Microbalances are highly susceptible to minute vibrations, which can be caused by:
• Strong winds that sway the building (or adjacent buildings)
• High tides or waves near a seashore
• Movement of people, handcarts or forklifts, etc.
• Trains or automobiles running close by
• Distant earthquakes, etc.
• Vibrations such as those above are often indiscernible to humans but strong enough to make a microbalance unstable.
Here is a list of what you can do to minimize the effects of vibrations:
1. Install the microbalance in a corner of the room next to a wall, but not touching it.
The center of a room has weaker construction, and the floor tends to shake more easily. On the other hand, there are usually structural supports in the corners of a room which make them less likely to shake.
2. Find an area where people’s passage can be kept to a minimum.
If possible, a dead-end area with low foot traffic should be selected. Also, avoid an area near a door, whose opening and closing can cause disturbances such as vibrations and air movements.
3. Set-up the microbalance on a heavy, rigid workbench, where no activity other than weighing is to be conducted. A dedicated weighing table is best.
The bench should be separated by a few centimeters from the wall and other workbenches/tables in order to prevent vibrations being transmitted.
4. Use a passive anti-vibration table recommended by the balance manufacturer.
Note that active anti-vibration tables employing costly air suspension actually become a source of vibration themselves and are not suitable for use with microbalances.
5. Do not perform measurements after (not to mention during) earthquakes or while a low-pressure system such as a thunderstorm is passing.
There is presently no established method of stabilizing low-frequency vibrations caused by these phenomena. Further, if the building is constructed as a quake-absorbing structure, once an earthquake occurs it may take several days for the microbalance to achieve stability again.
6. Lower the weighing speed of the microbalance.
Most balances today enable you to adjust the response characteristics whereby you can trade-off speed against stability.
Finally, it is desirable that the place is far away from routes with high traffic or heavy objects moving, and on as low a floor as possible of a rigid building built on a solid foundation, preferably the ground floor.
Tip #2: Ensure that the ambient temperature is stable.
Changes in ambient temperature affect not just the measurement accuracy but also the stability of the zero point.
The movement of the zero point is not normally apparent on the display while the balance’s zero tracking is activated. However, a zero point that is drifting or fluctuating rapidly will easily affect results by seriously worsening the repeatability of a microbalance.
Here is a list of what you can do to minimize the effects of temperature variation:
1. Maintain the room temperature within a certain range. Use an air conditioner as necessary.
Daily temperature fluctuations of 4°C or less (within 10 to 30°C) and short-term fluctuations of 0.2°C/30 minutes or less are recommended.
2. At the same time, keep the microbalance away from the air conditioner vent and cover it with an external breeze break (draft shield).
While air conditioning can keep the temperature in the room at a steady level, it also generates airflow.
Further, the on/off control of the air conditioner around the set temperature can cause repeated temperature changes of about 0.5°C. Such airflows combined with minute temperature fluctuation will have a particularly destabilizing effect on a microbalance.
As a countermeasure, the microbalance should be arranged so that it is not directly hit by airflows. In addition to keeping a distance from the air conditioner, the use of a large, external breeze break that covers the entire microbalance unit has proven to be highly effective and is therefore strongly recommended. It is also a good idea to have a partition between the air conditioner and the set-up area.
3. Keep any heat generating devices (e.g. furnace, lamp, etc.) far away from the microbalance, or if possible, out of the room.
If you cannot move those devices, do not perform measurement while they are in operation.
4. Avoid installing the microbalance in areas close to external air (near windows, doors, etc.) or subject to direct sunlight.
Also, walls that have outside air on the other side often go below or above room temperature. For this reason, it is best to install the microbalance near a wall that has another room on its opposite side.
5. Set up the microbalance on a non-metal workbench of low thermal conductivity.
The workbench should be separated by a few centimeters from the wall in order to prevent heat being transmitted, not to mention vibrations.
6. Find a large room for installation and limit the number of people entering at the time of measurement.
Human body heat can easily increase the temperature of a small room.
Tip #3: Ensure that the ambient humidity is stable.
Zero-point drift is also caused by moisture slowly being accumulated on or released from the weight sensor due to a shift in humidity.
Control changes in humidity, using an air conditioner as necessary. Daily humidity fluctuations of 10% or less is recommended. To check out the selection of A&D Weighing products, visit our page here.