Loss on Drying (LOD) Moisture Balance analysis is based on drying a sample and comparing the difference in weight before and after drying.
Determining the specs, and finding the cost of the best LOD Moisture Balance for your application can be frustrating, confusing and time consuming. There are more than 20 manufacturers of LOD moisture instruments. Most have more than one model available. To make the evaluation even more complicated, the prices for these instruments range from just below $1,000 to over $15,000. Many of these prices are not widely published.
In this exploration, we want to provide a guide to understanding the range of choice and cost among these many LOD Moisture instruments.
We'll address the following questions:
- What are the key specifications to consider?
- What are the important performance aspects?
- How are costs related to these factors?
The Electronic Balance
The common element in all LOD Moisture Analyzers is an electronic balance. This performs the measurement of before and after drying weights. It is the foundation of the LOD method.
Balance specifications are readily available in the manufacturers' brochures and data sheets. The important specifications are linked to:
- Balance Capacity
- Balanced Sensitivity
- Balance Repeatability
Of the three, sensitivity and repeatability are the most important.
Weight ranges of moisture balances vary from as low as 12 grams to as high as 200 grams.
Most loss on drying applications use sample weights below 10 grams. Thus, balance capacity is not a critical consideration.
Sensitivity, or resolution, of a balance is the smallest increment of weight change that can be detected. It is a way of defining the precision of a LOD moisture measurement.
Based on balance sensitivity, three clear groups of moisture analyzers can be identified.
The first group includes balances with a sensitivity of 0.01 grams. These are sometimes referred to as "two place balances", and are on the low end of the cost scale. Two place balances normally provide readouts between 0.1% to 0.5% moisture depending on the specific model.
The next category are instruments with sensitivity and resolution of 0.001 grams. These analyzers use a three place balance. The moisture readability of three place instruments ranges from 0.1% to 0.05%, depending upon the repeatability of the balance. The largest percentage of LOD balances are found in this category.
Moisture analyzers that use analytical balances with sensitivity/resolution or 0.0001 grams represent the highest cost category. Most of these four place instruments show test results to a precision of .001% moisture. These instruments are designed for precise and usually very low moisture requirements.
A starting point in the selection process is to determine the level of precision needed for your product. This involves defining the balance resolution/sensitivity and repeatability needed. This information can be found in manufacturer’s specifications under “Balance Resolution and Balance Repeatability”.
The repeatability of balance can be viewed as the smallest increment of weight that will repeat from test to test.
This specification affects the reliability of the last digit of the balance readout, both for weight and for moisture %. This characteristic is normally stated in grams or milligrams.
The impact of differences in repeatability can be seen in this example:
Consider a comparison of two three place balances using a 5 gram test sample. The first model has a repeatability of +/-.005 grams and the second has a repeatability of +/-.001 grams. The first model would provide a result within 0.2% of the moisture. The second would provide a result within 0.04% of the moisture. In some applications this is a significant difference.
Application and Features
After selecting the category of analyzer that will provide the desired precision, the next aspects to define are where the analyzer will be located and how it will be operated.
- Will it be used in a pristine laboratory environment or on a plant floor?
- Will the operators of the instrument be trained laboratory personnel or people assigned to testing as a collateral function?
If the location of the analyzer is not in a laboratory setting or if the operators are not trained in test equipment practices, the more rugged models are better choices.
With the moisture balance type, defined, relevant subsidiary functions need to be evaluated. These include the number of test methods that can be stored, complexity of testing profiles such as temperature ramping, and automatic shut-down algorithms. There is a wide variety of these options among the three place moisture analyzers.
The full range of costs across the many moisture balance models is not published. However, we have endeavored to get reasonably valid estimates for each category. The range between high and low is affected by the characteristics of ruggedness, operational repeatability, uptime and operating features.
The range of costs shown here represents the high and low prices we found for moisture analyzers in each balance category:
|Expected Price Range
|Two Place Balances
|<$1,000 to $ 2,500
|Three Place Balances
|$3,500 to $ 5,000
|Four Place Balances
|$5,500 to $12,000
Special Category Microwave Heating Technology: Microwave instruments are used for quick readings and for samples needing special drying processes. The instruments generally use four place balances and cost in excess of $15,000.
These prices were collected, where available, from listings on the internet, from quotations obtained from manufacturers, and estimates developed in conversations that CSC personnel had with users of other moisture analyzers.
The overriding considerations in the cost of moisture balances is the sensitivity and repeatability of the electronic balance used. Secondarily, the ability to withstand less than pristine conditions and operator abuse is a strong cost factor. When the first two cost influencers are defined, subsidiary functions have little effect on cost.
As with most things related to measurement instrumentation, confusion arises because of the always present opening answer to most questions:
We hope we have helped get at much of the “it depends” answer to the question to “What Does A Moisture Balance Cost?”
If you found this article useful, please share it with associates involved with measuring moisture.
As befuddled as ever,
P.S. Did you know that you can subscribe to these exposés, rants, raves and ramblings? All you have to do is enter your email address into the box just to the right of the title.
P.P.S. Take a look at one of the Tough Moisture Balances. Click in the Box.