Frequently Asked Questions

Frequently Asked Questions


  • CONSUMABLES - AQUALAB Are METER products safe?

    What is Prop 65?

    In 1986, California voters approved an initiative to help them make informed decisions about the products they buy. That initiative became known as Proposition 65. Proposition 65 requires the state of California to publish a list of chemicals known to cause cancer/ reproductive harm. You can learn more about Prop 65 here.  

    Why do METER products have a Prop 65 warning?

    METER is required by California law to post a warning on any product that might be sold in California if it contains or might contain one of the more than 900 chemicals known to the state of California to cause cancer and/or reproductive harm. Because consumers learn about our products from our website, we are required to post these warnings on the product web pages as well. California residents are used to seeing these notifications on many products, including household items, electrical wires, electronics, jewelry, dishes, flashlights, cosmetics, skincare products, and much more. People who live outside the state of California may be surprised and alarmed by these notifications. It is important to know that nearly all electronic products require the notification label even though the chemicals involved may only be potentially harmful when eaten in large quantities.  

    Are METER products safe?

    A Prop 65 warning does not necessarily mean a product is in violation of any product safety standards or requirements. Because METER sources manufacturing materials from other suppliers, we provide the warning in order to acknowledge that METER products may contain one or more of the chemicals listed. However, it’s likely that those chemicals are in such small amounts that they fall into the no-significant-risk category. To be safe and compliant, we have elected to label all product web pages and packaging with this warning.

    What types of chemicals are on the list?

    You can find a list of Prop 65 chemicals here.


  • AQUALAB TDL Are tunable diode laser (TDL) sensors affected by pressure fluctuations? Do results need to be normalized against daily atmospheric pressure?

    The TDL measures water vapor concentration by scanning a single spectral water vapor absorption line at 1854 nm. The absorption line is not really a “line”, it has width and a “bell” shape described by a Lorenzian function (similar to a Gaussian, but broader). As with all spectral lines, increases in ambient pressure decrease peak height and increase peak width. This is known as pressure broadening. The peak area, however, is fairly insensitive to pressure variations.

    METER’s AQUALAB TDL measures peak area, and is therefore insensitive to pressure variation. There remains, however, enough sensitivity to require compensation. A built in barometer sensor measures atmospheric pressure and compensates for day to day atmospheric pressure fluctuations. Larger changes, which would occur if the instrument were installed at a new location with substantially different elevation from where it was calibrated, may require an adjustment in the calibration. This is easily done using METER calibration standards.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB How can I minimize moisture migration in hygroscopic products during sampling?

    The best approach is to put the water activity instrument and the sample into controlled humidity conditions. Use a glove box, or get the sample inside the chamber as quickly as possible to prevent water uptake from the environment. With an instrument that maintains the seal in the chamber, it’s possible to perform consecutive readings. But if the instrument requires pulling out the sample to take a new reading, the water activity will continually change as the sample takes up more and more moisture.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB Is the whole tablet measurement of value?

    It depends if the tablet is non-coated or coated. If the coating material can absorb water, there is a critical water activity where the coating material will begin to break down. Thus, if monitoring that aspect of the product, then reading the water activity of a whole tablet would be important.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB Would you recommend breaking up a tablet with a mortar and pestle?

    A mortar and pestle is a valuable tool for sample preparation because it breaks things apart without being too excessive. You can achieve the same effect with a coffee grinder or food processor, but use only a couple of quick pulses. Process just enough to break the sample apart without grinding it.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB When testing finished pharmaceutical products such as tablets, should you test the entire tablet? Or should the tablets be crushed or ground?

    If the tablet has no coating, there won’t be a significant difference in water activity whether crushing it or reading it whole. If the tablet is coated, crush it to expose the interior. Don’t grind it. Otherwise, the water activity meter is only testing how effective the coating material is.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB How do you read water activity in large, dense products, such as brazil nuts?

    Break large products into pieces. This will keep read times shorter. This will also make sure you are measuring the water activity of the center of the product, not just the exterior.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB Does freezing a product increase its water activity?

    It depends on the freezing process. If the product is not frozen correctly and cells begin to rupture, the water activity may change. Remember to thaw a frozen sample before testing, as water activity can’t be read in a frozen state.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB Does temperature change the water activity of a material?

    There’s no good way to predict which types of products are sensitive to temperature, but reading a product at a series of different temperatures will show which products are sensitive. Meat products tend to be fairly stable, however some powdered compounds and sugars are more affected by temperature changes.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB What would be the best way to prepare an oily meat product for testing?

    An oily product requires longer read times. Breaking a product into smaller pieces will help, but don’t grind it. Grinding will tear apart the tissue structure and affect water activity. Slice it or pull off pieces to put into a sample cup.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB How long can samples be stored in Whirl-pak bags before water activity is affected?

    Samples can typically be stored whole in a Whirl-pak bag for half a day without a significant impact on water activity. If you grind the sample, however, you can cause substantial changes in water activity within five to ten minutes. For longer term storage, to store ground samples, or to send a sample to another lab, use a parafilmed sample cup with a screw top cap or a foil pouch.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB My product is coated with fat. Will that affect the water activity reading?

    All coatings impact water activity readings because they act as barriers to water molecules moving out of a product matrix and into the vapor phase. If your product has any kind of a coating around it, you need to break the sample apart before measuring.

  • AQUALAB TDL - AQUALAB Are there any sample limitations for the TDL?

    The TDL was designed specifically for use with volatile materials. We have tested alcohol, propylene glycol, acetone, gasoline, and other organic solvents without interference. The only samples you should be cautious with are those considered to be highly corrosive as they may damage the block coating or laser housing.

    Cleaning immediately after running corrosive samples is highly recommended to prevent corrosion of your instrument. You can run samples in liquid or solid form as long as the samples fit into our sample cup.

  • AQUALAB TDL - AQUALAB Do I need a new multipoint calibration for each temperature?

    Yes. The calibration using the laser is temperature dependent. The instrument comes factory calibrated for 25°C. If you wish to run at other temperatures, a multipoint calibration must be done at that temperature before you can proceed.

  • AQUALAB TDL - AQUALAB Why won’t my instrument verify within your specifications?

    If the TDL is not verifying, the first thing that should be done is to clean the chamber. If cleaning does not resolve the issue, try performing a multipoint calibration. If the multipoint calibration is not holding from day to day, please contact your METER Food Support team for further assistance.

  • AQUALAB 4TE - AQUALAB 4TEV I am getting a contaminated mirror error. What do I do?

    If you see an error message stating “Contaminated Mirror,” it is indicating that the mirror surface is contaminated. Clean the instrument following the recommended steps and re-run the sample to determine if this resolved the problem. If the error message continues to pop up on a certain sample, there may be volatile materials that are interfering with the chilled mirror sensor. If you have questions regarding the sample and how to determine if that is the cause, contact your METER Food Support team for additional support.

  • AQUALAB 4TEV - AQUALAB Do I need to clean the white filter in my TEV instrument?

    The white Teflon filter in the TEV models should never be cleaned with cleaning solution, IPA, or water. When cleaning, work around this filter and do not get it wet. If the filter is cleaned, it should be replaced with a new filter. The filter should also be replaced periodically as part of your standard maintenance. If you run a high volume of products containing volatiles, the filter should be replaced more frequently. Every month or every three months are common intervals.

  • AQUALAB 4TEV - AQUALAB How do I know what sensor to use on the TEV model?

    The TEV model contains two sensors: the chilled mirror dew point sensor and a capacitance sensor. The sensor can be selected in the configuration menu. The dew point sensor is the most accurate at ± 0.003 and should be used for all materials not containing volatiles. If the product contains volatile material, the capacitance sensor should be selected as those products will interfere with the mirror. The capacitance sensor has ± 0.015 accuracy (less than that of the dew point sensor) and should only be used for products containing volatiles.

  • AQUALAB 4TE - AQUALAB 4TEV The instrument will not read the standards correctly. What should I do?

    If the standards read out of specification during a routine verification, follow the instructions in the manual and clean the instrument. Ninety-eight percent of all out-of-spec readings can be resolved with proper cleaning. If after two thorough cleanings, the instrument is still out, a linear offset can be performed.

    The linear offset should only be performed when both standards are out of spec by a similar amount. If the standards are out by varying degrees, try resetting to factory default in the calibration menu and starting over. If that fails to correct the problem, contact customer support for further assistance.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB How often should I run the verification standards?

    This will depend on the frequency of use and the environment the instrument is operating in. If the instrument is being used daily, we recommend a daily verification prior to running samples. If the instrument is used sporadically, verifications on the day of use are sufficient. In manufacturing environments that are dusty or greasy, involve samples that are messy, or running multiple shifts per day, the verification may need to be done each shift. This is particularly important if water activity is part of a release specification.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB What standards should I use to verify?

    You should always select two standards that bracket your product range. A two-point verification is necessary to evaluate the factory calibration and ensure the slope is correct.

    To ensure the instrument is reading correctly across your product range, and to satisfy audit requirements, select two standards that bracket or are closest to your working range for routine verification. We offer seven standards that cover a broad range of water activity values.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB Why do I get long read times?

    Long read times could be caused by a number of factors. The four most common causes are listed below.

    1. The most common is that the instrument needs to be cleaned. Lack of cleaning or improper cleaning frequently causes long read times.
    2. Sample type: High fat, viscous and low water emitting samples all take longer to equilibrate in the chamber. This is sample dependent and long read times are necessary to give accurate, fully equilibrated results.
    3. Volatile ingredients such as alcohols, propylene glycol, and acetic acid can interfere with the chilled mirror sensor and cause unstable readings and extended read times.
    4. A damaged or bent fan blade in the chamber. If the fan is damaged and not working correctly, the removal of boundary layer moisture on the mirror surface is delayed, extending the read times.


  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB What is the accuracy of readings in the low emitter sensor setting?

    An instrument with a low emitting mode allows the user to manually make trade-offs between speed and accuracy. To investigate the low emitting mode, take a reading of the product in the standard read mode, and record the water activity value and read time. Then, in the low emitting mode, take a reading of the sample at the best accuracy setting and record the read time. Continue adjusting the accuracy level and recording readings and times. The goal is to remain close to the original water activity value, while saving read time. This will determine what accuracy setting is best for a particular product.

  • AQUALAB 4TE - AQUALAB 4TEV - AQUALAB TDL - AQUALAB What percent propylene glycol or ethanol is allowable in a formulation before it causes problems in dew point (chilled mirror) instruments?

    Volatile components in different sample matrices are dependent upon the sample. If using propylene glycol in one product, there may be a noticeable impact on chilled mirror readings at 0.5%. In a completely different product, it might be 2-3%. Generally, propylene glycol will be the most problematic component. For concerns about whether or not a concentration in a product is enough to be a problem, feel free to contact our support department. They will perform tests that show whether the volatiles in a product are impacting the chilled mirror method. If so, using the TDL sensor (which is unaffected by volatiles) should solve the problem.