Why Cheap Soil Moisture Sensors Fail (And How to Choose One That Lasts)

A while ago, a customer reached out to us about the frustrating unreliability of inexpensive capacitive soil moisture sensors. They'd experienced the common issue of those "5 for $10" sensors from online marketplaces failing, attributing it to "moisture penetration of the PCBs." This customer's experience is far from unique. Many people encounter similar problems, often misattributing the failures to the PCB material itself absorbing moisture.

The rise of online marketplaces has undeniably transformed our shopping habits, offering convenience and affordability. However, when it comes to specialized equipment like research-grade sensors, these platforms often fall short. Is a marketplace known for low prices and fast delivery the right place to source precision instruments?

The answer, unfortunately, is often no.

But let's shift focus. I want to discuss how we design and manufacture our sensors, such as the APAS T1 soil moisture sensor, to withstand harsh environmental conditions. Our sensors are built to be robust, capable of being buried, exposed to the elements, or even submerged in water without compromising their functionality.

APAS T1 soil moisture sensor (originally developed by DurUntash Lab, LLC, San Diego, CA)

While moisture can indeed damage electronic circuitry, the culprit isn't typically moisture seeping into the PCB material itself. Instead, the problems arise from corrosion of electrical junctions, damage to components, and short-circuits, especially when impurities like salts are present due to their high electrical conductivity.

Using PCBs as soil moisture sensor electrodes is a standard practice, but proper protection of the circuitry is crucial. The most common method, "injection molding" of plastic or rubber, has limitations. While it offers initial protection, these sensors often have a short lifespan, typically one to two years in the field. They also struggle to withstand the mechanical stress of installation and regular use.

At our company, we prioritize durability. The electronic components of our APAS T1 sensors are protected by a rugged, electronic-grade epoxy that resists moisture, humidity, corrosion, fungus, and static discharge.

Here's how we ensure the longevity of the APAS T1 soil moisture sensor:

• The APAS T1 measures soil water content using a 4-layer PCB sensor blade. The electrodes are embedded within the middle layers, completely shielded from moisture and soil electrical conductivity (EC). This design also eliminates concerns about surface scratches.

  
  

• The electronic components are first encased in a sturdy plastic cover and then fully encapsulated in our durable, electronic-grade epoxy. This creates a robust sensor head that withstands harsh environmental conditions.

  
  

The longevity of our sensors is remarkable. APAS T1 predecessors manufactured over a decade ago remain fully functional. While this extreme durability might raise environmental concerns, it's undoubtedly a significant benefit for our customers.