Computrac Moisture Analyzers

Operation and Performance Comparison

MAX 2000, MAX 1000 Series Analyzers

     The MAX 2000 and MAX 1000 Moisture Analyzers use state-of-the-art technology to monitor and control test temperatures to assure consistent, reliable moisture results. These units use platinum RTD (resistive temperature device) to measure the temperature generated from the heater coil. This information is relayed to an advanced microprocessor, which controls and limits the heater output to reach and maintain the programmed test temperatures without overshoot.

     Factory calibration for the MAX 2000 and MAX 1000 Moisture Analyzers is performed using a proprietary calibration device that utilizes an N.I.S.T. traceable RTD positioned at the sample height to calibrate and verify temperatures in the instruments from 60 C to 275 C (225 C in the MAX 1000). Measured temperatures at the sample level are recorded into memory and internal constants are adjusted using sophisticated regression algorithms to correlate temperatures measured at the sample surface with the heater's RTD and heater coil output. Thus, the temperature displayed on the display of the instrument is the temperature as measured at the sample's height. An optional accessory for the MAX 2000, the Temperature Calibration Module, allows the user to perform the same calibration and verification on site.

     The MAX 2000 and MAX 1000 Moisture Analyzers have programmable ending criteria which permit the end-user to select the optimum test conditions for their test sample. The available programs are "predict," "rate," and (for the MAX 2000) "time." The Computrac patented "predict" ending criteria ends the test when the difference between the predicted and the actual moisture content agree within a certain value. In the automatic mode, this value is based upon the moisture content of the sample. The "rate" ending criteria ends the test when the moisture evolved from the sample in a minute's time falls below the programmed threshold. The "time" ending criteria runs a fixed time test to determine moisture content (similar to a standard oven-drying test).

The Max 2000 offers:

• Temperature calibration with an N.I.S.T. traceable RTD positioned at the sample height.
• Increased chamber size to accommodate larger samples.
• Heater element technology focuses radiation on the pan to provide greater efficiency than found in the Max 50 or MA series
• N.I.S.T. traceable calibration methods for the balance

Max 50 Series Moisture Analyzers

     The Max 50 series analyzers (Max 50, Max 20, Max 10, and the LX-10 and the LX-50) use early 1980's technology for heat control. These units use a soldered RTD and a "temperature offset" to compensate for the temperature difference measured between the RTD and the sample surface. This offset can be as much as 19 C depending upon the instrument's test temperature, programming, and the sample size. The Max-50 series units measure the resistance output from the temperature sensor based upon fixed milliampere input. Changes in resistance within the RTD circuit (such as corrosion), RTD position relative to the burner coil, electronic drift, and sample sediment on the sensor will all affect the sample's perceived testing temperature.

     The Max 50 series moisture analyzers use one of (or a combination of) three fixed ending criteria to predict the endpoint moisture value. The ending criteria designed for low moisture samples or for greatest accuracy is designated the "EC06" program. The EC06 program requires that the difference between predicted and actual moisture be less than 0.015%. It also requires successive predictions to agree within 0.0075%.

     The most commonly used ending criteria in the Max series is the "EC97" program. This program requires that the difference between predicted and actual moisture levels be less than 0.2425%. It requires successive predictions to agree within 0.12%. The "EC255" program is designed for high moisture samples or for fastest test times. This program requires that the difference between predicted and actual moisture levels be less than 0.6375%. It requires successive predictions to agree within 0.32%.

     In addition, the Max 50 series firmware "relaxes" or loosens the ending criteria as the moisture level in the sample increases. At higher moisture levels the criteria are increased by 0.01% for each 10% increase in moisture content. This enables shorter test times at higher moisture levels, without a loss in statistical precision.

     Other specialized programs exist for the Max 50 series to accommodate customers' specific testing needs and requirements. Contact Arizona Instrument Customer Service for specific information regarding these programs.

MA Series Moisture Analyzers

     The MA series moisture analyzers (MA-5A, MA-2A, MA-1A) use technology originally developed in the late 70s. These units use a semiconductor junction temperature transducer, which generates an output current proportional to temperature. Like the Max 50 series, the MA units also place the temperature sensor above the sample position. The difference between temperature at the transducer and at the sample surface was experimentally determined and programmed into the software.

     The prediction ending criteria used by all the MA series analyzers requires that the difference between predicted moisture and the actual moisture is less than 0.25%. It also requires that successive predictions agree within 0.062%. This prediction algorithm is most similar to the Max series' "EC97" ending criteria.

Computrac Comparison Chart

Testing Temperatures

     Testing parameters determined for one of the Computrac moisture analyzer models (or series) will not necessarily be identical for another model or series. Differences in the heater size and configuration, balance, electronics, microprocessors, and the temperature control circuits all combine to create different and unique requirements for different test samples. In general, the MAX 2000 (or MAX 1000) will test at temperatures slightly lower (10 to 15 C) than those used in the Max 50 series analyzers. When comparing test temperatures between the MAX-2000 (or MAX-1000) and the MA series analyzers, the newer MAX 2000 (or MAX 1000) model will typically test at a test temperature lower (10 to 30 C) than the temperature used on the older MA system.

     In order to determine the correct test temperature in any of the Computrac moisture analyzer models, products should first be tested using the primary method (such as the standard oven, vacuum oven, or Karl Fisher titration) to determine their moisture content. Next, the sample should be tested on the Computrac moisture analyzer.

     To determine the correct test temperature that produces accurate, reproducible results that correlate with the reference method, see the instrument's User's Manual. For the MAX 2000 (or MAX 1000) refer to "Determining the Proper Test Temperature" in the section titled "Performance Enhancement." For the Max 50 and MA series analyzers, this is described in the section "Determining the Proper Test Temperatures."

Summary

     The Computrac Moisture Analyzers all use the patented prediction algorithm to determine the moisture content of a product quickly and accurately without taking the sample to absolute dryness.  Over the years, Computrac has taken advantage of advances in technology and electronics, as well as customer feedback, to refine the resolution of the balance and more tightly control the test temperature to assure consistent reliable test conditions. Each generation Computrac moisture analyzer represents the latest in technology and engineering available at the time of introduction.   The MAX 2000 and MAX 1000 continued the Computrac legacy established by the innovative MA-5A series and carried on by the dependable Max 50 series analyzers to provide the most accurate, reliable moisture analysis possible to either the production floor or the research or quality control laboratory.