Research-Grade Substrate Moisture and Temperature Sensor

APAS T1

APAS T1 is a research-grade  substrate moisture sensor with a large volume of influence. The APAS T1 is designed and optimized for measurements in soilless media (e.g. rockwool, coco coir), and can also measure accurately in the soil. The sensor  goes through a multiple-stage tuning to minimize sensor-to-sensor variability and provides temperature-compensated readings (when combined with DurUntash readout devices) to maximize overall measurement accuracy. The APAS T1 can be easily interfaced with the Raspberry Pi using DurUntash sensor adapters. The APAS T1 can be used for monitoring water content and irrigation scheduling, as well as performance evaluation of irrigation systems in outdoor and controlled environment agriculture.

Features

  • Measures in soil; optimized for moisture measurements in soilless media (rockwool, coco, etc)

  • Optimized design; much lower sensitivity to air gaps due to installation compared to other sensor brands

  • Temperature measurements and temperature-compensated moisture readings (when combined w/ DurUntash readout devices and data acquisition equipment)

  • Large volume of influence (~800 ml); better indicator of root zone moisture

  • Reduced cable and EMI noise; snap-on ferrite core on the cable 

  • Sensor-specific calibration coefficients stored in sensor memory

  • Ruggedized design; electronics protected by epoxy fill

  • Ideal for IoT applications; 64-bit digital ID and low power consumption

  • 20-MHz measurement frequency minimizes sensitivity to substrate texture and salinity

  • Compatible with Arduino; easily interfaced with Raspberry Pi

  • Dedicated 4-channel data logger, dedicated reader and configuration software

DurUntash Lab APAS T1 rockwool substrate & soil moisture temperature sensor

Designed by Scientists

They say "necessity is the mother of invention". We needed a reliable and affordable moisture sensor that we could use in our research at university or recommend to farmers. Over the years, we had tried too many soil moisture sensors that horribly failed us. So this time, we decided to develop our own sensor. We took the advantage of our academic experience and expertise in agriculture, irrigation water management, soil science and electronics, and designed a sensor to meet the needs of our research group and the agricultural community. ​You can learn more about the history of the APAS T1 here.

Calibration

​​Sensor-Specific. Every APAS T1 sensor has non-volatile memory, which allows for storing sensor-specific calibration coefficients. This stage adds to the flexibility of sensor application, removes sensor-to-sensor variability, and allows for individual sensor calibration for specific substrate, soil or condition. Every time that a sensor is read, these sensor-specific calibration coefficients are automatically applied to moisture readings. Only research-grade APAS T1 sensors go through this stage.   

Medium-Specific. We have carried out a variety of experiments in both soil (e.g. clay, silt, sand) and soilless (e.g. rockwool, coco coir) media. This stage is called medium-specific calibration and its goal is to ensure the APAS T1 sensor measures water content with the highest accuracy in any given medium. In the process, we have also taken this into account that sensor installation type can affect the readings. The calibration coefficients are embedded into the firmware of all DurUntash Lab readout devices, and automatically applied to sensor readings. 

Accurately Measures in Soil, Rockwool and Coco Coir

Very often, we get this question that what growing media your APAS T1 moisture sensor can accurately measure in. The answer is in almost “all media types” including soil and soilless media, as long as the sensor is installed correctly. The APAS T1 comes with the plus of being already optimized for soilless media in terms of size, shape, electronics and calibration. The soilless media that are supported include rockwool blocks, coco coir, rockwool mini cubes, and basically any medium that falls into the definition of soillessThe only thing that is different across different media is the installation procedure. Each medium requires its own method. You can read more about different media and how it may affect the sensor installation in this blog post.

APAS T1 soil moisture sensor for soilless media, rockwool, coco

Optimized for Less Sensitivity to Air Gaps

The greatest feature of the APAS T1 is that it is much less sensitive to air gaps in the soil/substrate when compared with most sensor brands. This is because we have optimized the size and shape of the APAS T1 (Related article: "Why Size and Shape of a Soil Moisture Sensor Matter: Sensitivity to Air Gaps"). The sensor has a large probe surface area that maximizes contact with the substrate. A smaller sensor (for example sensors with prongs made of short steel rods) would be more sensitive to even small air gaps, because most of the sensor surface might not touch the soil or substrate. Some sensor manufacturers claim that they have solved the problem of air gaps by increasing the sensor's volume of influence, but this is a false claim. Numerical analysis by scientists have shown that 90% of the TDR sensor measurement area only extends to about 0.01 m from the probe surface, meaning that moisture sensors are extremely sensitive to air gaps. If there is an air gap, most of the electromagnetic wave (no matter how powerful) is reflected from the air-soil interface and will not penetrate the substrate. The problem with air gaps is more pronounced if you are using a small sensor to monitor coco coir moisture, because coco coir tends to expand and shrink as a result of absorbing or losing water. 

Temperature-Compensated Moisture Readings

Substrate temperature (Ts) is a useful parameter in monitoring crop growth. It is also a key factor contributing to the inaccuracy of water content measurements by almost all commercial soil moisture sensors (Related article: "Why Soil Temperature Fluctuations Result in Inaccurate Soil Moisture Measurements?"), because Ts changes moisture sensor readings. This can cause moisture readings to Go Up when the substrate/soil is actually drying out and vice versa. It is worth knowing that sensor temperature sensitivity also affects the calibration process and contribute even more to the inaccuracy.

 

We have added an accurate temperature sensor to our design. The effect of Ts on the electronics is minimized in the circuit design. In addition, we have developed a transparent two-stage temperature compensation algorithm based on multiple regression analysis that takes both temperature and moisture readings and compensates water content readings for fluctuations that are caused by temperature change. The algorithm resides on the dedicated reader or data logger, and the whole process is worry-free, real-time and automatic. The algorithm is transparent, and the user has full control over it. The parameters can be adjusted, enabled/disabled to suit specific soil, substrate or condition.

Sensor Varieties

The research-grade APAS T1 sensor comes in two different varieties: 1) standard tip, and 2) sharp tip. The two sensor varieties share the same hardware. Both varieties of the APAS T1 come pre-programmed with sensor-specific calibration coefficients, and with a ferrite core (EMI noise suppressor) on their cable. In addition, the latest revision of the research-grade APAS T1 has a  sharper tip for easier installation in rockwool cubes. These features make the research-grade sensor great for both scientific research and irrigation scheduling, and allow it to work smoothly with DurUntash Lab data acquisition systems. 

DurUntash Lab APAS T1 substrate & soil moisture temperature sensor

Great for IoT Applications

A measurement time of 10 ms, low-power requirements (<15 mA @ 3.3 V), and a 64-bit digital ID stored in its on-board ROM make the APAS T1 an excellent choice for Internet of Things applications. In applications, where small battery is the only source of power, and hundreds of sensors may operate on the same network, our APAS T1 can save you a lot of headaches.

Large Volume of Influence

The APAS T1 has a large volume of influence to sensor size compared to other sensors in the market, which results in higher accuracy.  The sensor blade is only 8.5 cm, while it delivers an impressive 800 mL volume of influence. The volume of influence of most sensors in the market does not exceed 200 mL (typical). 

APAS T1 soil mooisture sensor large volume of influnce

Ruggedized Design

The circuitry of the APAS T1 is protected by a durable epoxy fill guaranteeing a long-lasting sensor that can be used over and over again for years to come. We have also added a strain relief connector to the design to make sure the cable internal wires do not break easily. To reduce wear and tear, unlike the common design approach in the market, the sensor cable connects to the side of the sensor rather than bottom. 

APAS T1 Soil Moisture Sensor Eposy Resin Injection

Dedicated Reader, Data Logger and Graphical User Interface

To give the user the best experience, we have developed a graphical user interface (SHUSHAN CVI), which can be used for both sensor readings and real-time datalogging and monitoring. The sensor output signal is compatible with most commercial data loggers, but we recommend our SHINAK 4P 4-channel sensor node (series) that is available in standalone and wireless models. You can also take sensor readings using our ISHTAR 1P-BLE Bluetooth-enabled sensor node. If you are interested in electronics and DIY, we also have open-source sensor readers that you can build at home.

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Datalogger
ISHTAR 1P-BLE

Optional Cable Length

The APAS T1 is available in three cable length options: 1.8 m (6 ft), 3.0 m (9.8 ft) and 4.5 m (14.8 ft). The cable length can also be easily extended using standard 1.8-m, 3-m, and 4.5-m extension adapter cables available from third-party sellers. Please read the APAS T1 user manual for more information.

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Applications

Moisture and temperature are recognized as important variables that influence plant productivity in both agricultural and natural ecosystems. Continuous monitoring of soil/substrate moisture is very important in different areas of science and engineering such as hydrology, soil science, geotechnical, ecology, meteorology, agronomy and controlled environment agriculture. Accurate soil moisture measurements are necessary tools in precision irrigation and water management. Substrate temperature is also a useful parameter in monitoring crop growth and can also be used for correcting moisture measurements. Soil moisture measurements can be used by farmers and researchers to determine water deficit and to specify the amount of water needed by plants.

California Proposition 65 Warning

This product may contain chemicals, which are known to the State of California to cause cancer, birth defects or other reproductive harm. Please go to the proposition 65 warnings website for more information.