What is Semi-Micro Weighing

There are lots of abbreviations, acronyms and unique names within the weighing industry.  Often there are lots of alternatives that mean the same thing.  Today I will discuss Semi-Micro weighing; what it is, what it is for and what we offer at OHAUS. 

The term ‘Semi-Micro’ covers a range of balances that sit between Analytical Balances (that have a readability of 0.0001g) and Micro Balances (that have a readability of 1µg).  A Semi-Micro balance has a readability of 0.00001g / 10ug.  Because of this it is also commonly called a 5 Place Balance (as it weighs to 5 places of a gram). Below are some of the categories and names used for laboratory balances.

• Micro Balance – 6 place balance – 1ug / 0.000001g readability
• Semi Micro Balance – 5 place balance – 10ug / 0.00001g readability
• Analytical Balance – 4 place balance – 0.1mg / 0.0001g readability
• Precision Balance – 3 place balance – 1mg / 0.001g readability (often also includes readability 1g>1mg)

Semi-Micro Balances are used for a range of applications, and because of this, there are a range of balances available to meet the technical and cost requirements of the operator. 

Laboratory Environmental Factors for Semi-Micro weighing

Due to the nature of such accuracy, when using a Semi-Micro balance, it is paramount that environmental factors are minimized (such as airflow and vibration). However, more so than Analytical and Precision weighing, even the smallest of external factors can dramatically increase the uncertainty of the results. Even when the external environment seems stable, one element that can really start to affect Semi-Micro weighing results is the effect of static electricity. Insulating materials like plastics (e.g. plastic weigh vessels), tend to accumulate static electricity when the ambient relative humidity (RH) falls below 45%. This can lead to measurement errors of several milligrams and significantly impact weighing results. In some cases, powdery substances that carry a static charge may cling to the walls of test tubes, rendering accurate measurement and cleanup problematic. There are a number of options to reduce the risk of static charges affecting your weighing results. Such as the OHAUS ION-100A Ionizer. This standalone device eliminates static charges by using two polarity electrodes that continuously generate positive and negative ions. These ions are attracted to ions of the opposite polarity, neutralizing the sample within a charged environment.

Semi-Micro Weighing in Academic Research Laboratories

Semi-Micro weighing is used in many research laboratories within academia.  This includes anything from weighing biological assays in molecular biology, to measuring trace elements of pollutants in environmental samples such as soil, water and air.  Using equipment that offers reliable results is essential within these research laboratories, not only for the credibility of students and their research, but for the laboratory and its funding.  The research itself is often trailblazing research that can develop and shape industries, taking projects in new directions and creating the basis for entire new sectors.  Because of these reasons we cannot underestimate the importance of choosing the right balance.  That said, funding is often more limited than established industries, therefore a lower cost, but ultimately very reliable semi micro balance is required. 

OHAUS offer the Pioneer Semi-Micro balance. Simple to use, with no complex features and a highly accurate loadcell offer reliable results at an affordable cost.

Semi-Micro Weighing in Test Laboratories

Within established laboratories Semi-Micro balances are also used for a wide range of applications, such as weighing filter papers within the automobile industry when testing emissions, or for advanced research in polymer development to weigh catalysts and additives during the synthesis of polymers.  In these types of industries, again the reliability of results is crucially important, but additional considerations may also be required.  Features such as user management to control which operator can perform which function, or consolidated batch report printing, to reduce the risk of error when recording multiple results.

For these environments we recommend the newly launched OHAUS Adventurer Semi-Micro balance.  Simple setup, accurate results and a 3-level user management setup, prebuilt into the operating system, make this the perfect Semi-Micro balance for many laboratory requirements. 

Semi-Micro weighing in the Pharmaceutical Industry:

The pharmaceutical industry, along with other highly regulated industries have very specific legal and regulatory requirements that need to be considered with using a Semi-Micro balance.  For example, the FDAs (U.S. Food and Drug Association) regulation: 21 CRF part 11, has requirements to ensure the reliability and integrity of the results from a balance.  These include additional security measures to restrict access to operators, an audit trail to show which operator performed which function, exportable electronic records and the ability to transmit the data elsewhere to be recorded.  Whilst the regulation also considers the entire laboratory system, and the way the quality system is being administered, so it is not possible to have a single balance that is in itself compliant, the pharmaceutical industry requires their Semi-Micro balances to ensure that compliance is made as easy as possible.  Because of this we have created and adapted the OHAUS Explorer balance to reduce the risk of non-compliance. 

The OHAUS Explorer Semi-Micro balances comes with strict 4 level user management system, that includes the ability to offer an auditor access to the audit trail (including operator log in details, weight readings and setting changes).  The Explorer also has the ability to quickly adapt to laboratory software, with in-built communication and command protocols, this allows the balance to be connected into a 21 CFR Part 11 complaint environment.  In addition to compliance the Explorer comes equipped with built in applications suited to the pharmaceutical industry, such as fill weight variation, that compares the weight of tablets and capsules within a batch, to ensure uniformity and consistency.  Using the fill weight variation application can reduce the time taken to perform standard operations, but more importantly it can reduce the risk of inaccuracies and errors when calculating the tolerances of the variation in pharmaceutical production.  Infrared sensors can be used to perform touch free operations such as controlling the powered draft shield doors, or the integrated Ionizer, reducing contaminants in high-risk areas. The Explorer also uses our most advanced Magnetic Force Restoration (MFR) loadcell, manufactured and finely tuned from a single block of metal, to ensure highly accurate weighing results.

In summary, Semi-Micro weighing is used in many industries, and therefore requires a range of balance options that cover features, regulatory compliance and cost.  For more information on the OHAUS range of balances, how to use them and for operator training please contact the OHAUS sales team.

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