Frequently Asked Questions
Environment Top FAQs
- Soil Moisture Sensor - ECH2O 5TE - GS3 Can your 5TE or GS3 tell me the soil salinity or the pore water EC?
Our sensors measure bulk EC, not soil salinity or pore water EC. Pore water EC can be derived from bulk EC using various models, including the Hillhorst model. This is described more in our application note about soil EC.
- SC-1 Leaf Porometer - ATMOS Why doesn’t the Leaf Porometer output transpiration like the LI-COR used to?
The SC-1 Leaf Porometer measures the vapor flux to arrive at stomatal conductance, which on the surface gives you leaf level transpiration. However, the leaf chamber of the SC-1 forces its own environment on the leaf, so the chamber steady-state transpiration will likely differ significantly from the environment steady-state transpiration. This is fine for stomatal conductance since the reading is taken within 30 seconds, but it doesn’t work for transpiration. We recommend you use independent atmospheric vapor pressure and leaf temperature measurements coupled with an estimate of leaf boundary layer conductance to calculate transpiration from the stomatal conductance measurement made with the SC-1.
- ECH2O 5TE - ECH2O 5TM - Volumetric Water Content - GENERAL - ECH2O EC-5 - ECH2O Why don’t your soil moisture sensors measure with 1% accuracy like some others spec’d?
There are two elements to the accuracy of time-domain reflectometry (TDR), frequency domain reflectometry (FDR), and capacitance sensors:
- How well the sensors measure the dielectric permittivity of the soil; and
- How well the calibration converts that measurement to water content.
Due to inherent variability in soil physical properties, it is impossible for a dielectric sensor to measure within 1% water content accuracy across a broad range of soil types, even with a perfect measurement of dielectric permittivity. Beware sensors that claim an unbelievable accuracy in all substrates.
- KSAT - LABROS How does KSAT calculate the temperature correction to obtain the saturated conductivity at the specified reference temperature?
KSAT uses the temperature dependency of the viscosity of water to recalculate the reference conductivity (at your specified reference temperature) from the measured value (at the measured operation temperature). Details are specified on page 11 in the KSAT operation manual (available as a pdf from the Help menu in the KSAT software).
- WP4C - LABROS What causes long read times in my WP4C?
Contamination of the sample chamber is the primary cause of long read times. The WP4C relies on equilibration of water vapor in the chamber with the sample. A dirty sample chamber can have samples that adsorb or desorb water vapor. This can lead to longer read times but is usually rectified by a good cleaning.
Unstable temperatures can also be a problem. Take care to provide a stable temperature environment for your WP4C and to keep your samples close to the temperature at which you intend to read them.
- SATURO - HYDROS What is the maximum measurable infiltration rate of the DualHead Infiltrometer (SATURO)?
The SATURO can measure a maximum field saturated hydraulic conductivity (Kfs) of 115 cm/hr.
- Soil Moisture Sensor - GENERAL Why doesn’t my soil moisture sensor read 100% VWC in pure water?
Testing your sensor in water can be a great quick check for basic sensor function, but it is a poor test for accuracy. The calibration of all METER soil moisture sensors is optimized for 0 – 50% volumetric water content (VWC), the usual range of soil water content.
Water will tell you if a sensor responds to a change in water content. But the reading itself will vary. Please contact firstname.lastname@example.org for recommendations to test the absolute accuracy of your sensors.
- Soil Moisture Sensor - GENERAL What does my soil moisture value in a frozen soil mean?
Volumetric water content (VWC) from a frozen soil will look much like dry soil. Your sensor will carry on merrily, but you will not see any change in water content until you start to get liquid water near the sensor again.
Food Top FAQs
- 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 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.
- The most common is that the instrument needs to be cleaned. Lack of cleaning or improper cleaning frequently causes long read times.
- 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.
- 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.
- 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.
- CONSUMABLES Can I reuse the standards or sample cups?
The standards we use are unsaturated salt solutions, which are created with high accuracy and precision. They are not reusable, however, as exposure to ambient conditions will begin to alter the standards. If they are kept in a sample cup with a lid, they can be kept for up to two hours but no longer. The sample cups are meant to be disposable. Residue left behind from the previous sample can impact your readings and introduce error. Repeat washing of the cups breaks down the coating and material can become embedded in the plastic, which can also introduce error. For consistent and accurate results, we do not recommend reusing the cups.
- FOOD Services How frequently should my instrument be sent in for service?
We recommend that instruments come in once per year for annual service and calibration. This is required if you must have a certificate on file showing instrument calibration. If the instrument is used heavily and in harsh environments, more frequent service may be needed.