Ultra-Microbalances

Ultra micro balance definition: An ultra micro balance is a highly precise weighing instrument offering seven decimal place readability (0.1 µg). Ultra micro balances are ideal for determining the weight of exceptionally small quantities of substances, often in the microgram weighing range. The highly sensitive weighing cell in an ultra micro balance enables samples as small as 30 µg to be weighed with extreme accuracy.

Watch our video of preparing samples with an XPR ultra-microbalance:

Applications that involve weighing very small samples with a high level of accuracy typically demand the use of an ultra microbalance. When weighing on an ultra microbalance only the tiniest quantities are needed . This is particularly important not only when substances are rare or expensive but also when they are toxic or have potent physiological effects. This is safer for the user of the ultra microbalance as well as more economical. Indeed, the savings made from using micro samples can soon pay for the ultra microbalance itself. Ultra microbalances are used in a variety of applications, including quality assurance and product testing. Common ultra microbalance applications include determination of particulate matter in emissions testing (filter weighing), ashing or incineration, measurement of coatings, and checking spillage quantities.

Visit our applications library page to learn more about weighing with an ultra microbalance.

Our ultra micro balance application videos can also be viewed here

There are some key factors to consider when the selecting the right ultra micro balance to suit your particular application:

1. What is the smallest amount you need to weigh?
2. What is the maximum amount you want to weigh?
3. How accurately do you want to weigh it? (What is the acceptable process tolerance?)
4. What are the negative consequences of an incorrect weighing result? (What is the process risk?)

Furthermore, understanding uncertainty is important to ensuring accurate results and avoiding errors. Every weight measurement on an ultra micro balance, and in fact on any balance, has a degree of uncertainty. At the lower end of the weighing range on ultra-micro balances, the uncertainty is almost entirely due to repeatability. It should be noted that it is repeatability that defines the accuracy of a weighing instrument and not readability. Readability is the smallest difference in weight that can be determined on your ultra micro balance. The actual smallest amount that you can weigh on your ultra micro balance is known as the balance's minimum weight. Below the minimum weight value, the uncertainty is too large for weighing results to be trusted. The minimum weight of your ultra micro balance is also dependent on your process tolerances and the process risk.

METTLR TOLEDO offers a free GWP^™ Recommendation service to ensure you select the right ultra micro balance according to your individual application and accuracy requirements. Ask your local representative for more details.

When weighing on ultra-microbalances, it is important to always wear gloves. Touching tools, containers and samples with your bare hands can transfer oils and dirt, which can affect weighing results. It is recommended that you use micro tweezers to transfer items to and from the weighing chamber on your ultra micro balance. To start a weighing task on your ultra micro balance, first press zero. Open the draft shield door, and gently place your weighing container on the weighing pan. Close the draft shield door and wait for the reading on the display to stabilize. Now press tare. Once you have dosed your sample, close the draft shield, and wait again for the reading to stabilize. You should avoid touching the balance or the weighing bench during the stabilization period because ultra-microbalances are highly sensitive to movement. Repeat the dosing procedure until you have reached the target weight, then record the net weight as shown on the balance display. Clean your ultra micro balance and the surrounding workspace after each use as well all the tools and equipment you used.

Watch our video, which explains how to weigh on an ultra-microbalance:

XPR ultra micro balances have built-in infrared sensors that enable you to open and close the door with just the wave of a hand, helping to speed up weighing processes and minimize vibrations.

Ultra micro balances have an exceptionally sensitive weighing cell. As such, any interaction from the user or the slightest disturbance in the environment can affect the measurement stability. All sources of vibration should therefore be avoided. The weighing performance of ultra micro balances can also be affected by air currents, dust, and temperature fluctuations. Ultra-micro balances should therefore be installed where the humidity and ambient temperature are maintained at a constant level. Installing an ultra micro balance close to windows, doors, vents, or in busy areas should be avoided.

Ideally, your ultra micro balance should be set up on a dedicated weighing table optimized for microbalance use in a low-traffic area, free from drafts. When first switching on your ultra micro balance, it is recommended that you wait for at least a few hours before using it to allow for temperature stabilization.

Temperature differentials within the weighing chamber can set up convection flows, which negatively impact weighing results. This occurs when the sample or the container is not at the same temperature as the weighing chamber. To mitigate this, use tweezers to handle samples and containers to prevent heat transfer from your hands, and allow samples, containers and tools to acclimatize to room temperature before use.

Our free micro-weighing guide has useful tips and tricks to help you get the most out of your ultra micro balance.

Particularly if you are using your ultra microbalance in microbiological and pharmaceutical environments, many of the substances you may work with could be toxic and pose a risk to personal health. When working with toxic and potent substances you should always wear appropriate personal protection equipment. Safety procedures should be in place not only to protect personnel but also to ensure samples do not become contaminated or cause other samples, your ultra microbalance, or the surroundings to become contaminated.

This video shows how METTLER TOLEDO'S ultra microbalances support safe weighing.

Our free white paper contains further information on how to stay safe when weighing hazardous substances.

XPR ultra microbalances incorporate METTLER TOLEDO's proFACT technology, which ensures ongoing weighing accuracy. proFACT automatically makes an adjustment to the balance whenever there is a change in the ambient temperature.

The calibration process serves as an assessment of the performance of your ultra microbalance. Ultra microbalance calibration should only be undertaken by an authorized calibration service technician.

As part of the ultra microbalance calibration service, the technician will usually make any necessary adjustments and determine its minimum weight. At the end of the calibration service, all test results will be documented in the calibration certificate to confirm that your ultra microbalance is working as expected. The calibration certificate is a necessary part of proving results traceability.

In the intervals between calibrations, routine testing by the user is essential in order to provide an early warning of any potential drift in the performance of your ultra microbalance, which could lead to weighing results that do not meet your accuracy requirements.

METTLER TOLEDO's Good Weighing Practice™ (GWP™) is a global scientific standard for the secure selection, calibration and operation of weighing equipment. Our GWP™ Verification service defines a performance verification schedule specific to your ultra microbalance and your applications. This includes calibration frequency, testing frequency, testing methods and test weights, all detailed in audit-proof documentation.

To learn more about why calibrating your ultra microbalance is so important, explore our calibration FAQs.

Ultra-micro balances are highly sensitive instruments capable of weighing down to a few micrograms. Therefore, the location of ultra-micro balances should be optimized to avoid external influences. Common influences include:

• Vibration: Ultra-micro balances should be located away from any vibrations, such as from mechanical equipment. In addition, ultra-micro balances should only be placed on a solid and stable weighing table.
• Drafts: Away from doors, air conditioning units, and busy aisles is the best location to place ultra-micro balances.
• Temperature fluctuations: Avoid placing ultra-micro balances near windows or heat sources.

Example measurement error of ultra-micro balances depending on their location in a lab: