Modbus-RTU RS485 Soil Moisture Sensor – What’s that?!

In a previous article – Soil Moisture Sensor – Getting Started with Arduino, we explained that there are two kinds of soil moisture sensor, i.e. resistive and capacitive. We also introduced Grove and some of the Grove soil moisture sensors. 

However, there is another kind of soil moisture sensor with MODBUS-RTU RS485 capabilities! They are known for their reliability, with many citing them as industrial-grade! In this article, we will be explaining what is RS485, Modbus, and these soil moisture advantages. We will also show you the different applications and some recommended products! Let’s get started!

Here at Seeed, we have four different RS485 Soil Moisture Sensors, all of which works flawlessly. All four of them are able to measure soil moisture as well as temperature as well! Two of them are also able to measure electric conductivity. Here are the different sensors:

Industrial Soil Moisture & Temperature Sensor MODBUS-RTU RS485, 0-2V Analog Voltage (S-Soil MT-02A)

This measure works by measuring the dielectric constant of the soil, to stably measure the soil volumetric water content. It works regardless of any soil types. The accuracy of its measurements conforms to the current international standard for soil moisture measurement!

This sensor is able to measure soil temperature as well, with high precision and sensitivity. It transmits the results of its measurements via MODBUS-RTU RS485. 

Industrial Soil Moisture & Temperature Sensor MODBUS-RTU RS485, 0-2V Analog Voltage (S-Soil MT-02B), with waterproof aviation connector

This soil moisture connector works similarly to the aforementioned one. The difference lies in this one coming with a waterproof aviation connector instead of hook-up wires. The waterproof aviation connector provides easy deployment as there is no need to use screws to connect the cable to the data logger. It can be used with SenseCAP Sensor Hub 4G Data Logger with a plug-and-play configuration with ease!

Industrial Soil Moisture & Temperature & EC Sensor MODBUS-RTU RS485 (S-Soil MTEC-02A)

This sensor is able to measure soil moisture, soil temperature, as well as soil electrical conductivity. Soil electric conductivity is the salinity of the soil, also known as the level of salts in the soil. 

It also works by measuring the dielectric constant of the soil, to stably measure the soil volumetric water content. It also transmits the results of its measurements via MODBUS-RTU RS485. 

Industrial Soil Moisture & Temperature & EC Sensor MODBUS-RTU RS485 (S-Soil MTEC-02B), with waterproof aviation connector

Similarly, the only difference this sensor has with the previously mentioned sensor is that this sensor also has a waterproof aviation connector instead of hook-up wires for easier connectivity. 

SenseCAP Sensor Hub 4G Data Logger

The SenseCAP Sensor Hub is able to connect up to 32 RS-485 sensors! Because the SenseCAP Sensor Hub is compatible with standard MODBUS-RTU RS485 connections, it may be used with virtually any industrial-grade sensor to transfer data to the cloud. It is extremely ideal for long-term remote environmental monitoring in outdoor application scenarios, as it is IP66 certified, waterproof, and dustproof. The data collected is sent to the cloud vis 4G/3G/2G.

Know your crops with a Soil Moisture Sensor!

Before we carry on any further, we need to understand what is a Soil Moisture Sensor. Like its name suggests, a soil moisture sensor is used to measure and obtain data on the amount of moisture in the soil. Having just the right amount of water for your agriculture is crucial, and it is impossible to visually observe and measure moisture levels in the soil with our naked eyes. A soil moisture sensor will make you care for your agriculture like a pro!

What is RS485?

Ref: Windmill

In short, RS485 is a standard defining the electrical characteristics of serial lines for use in serial communications systems. It is essentially a form of serial communication

Compared to serial communication, USB and ethernet are significantly more complex and expensive. Serial communication also has a deterministic behaviour to avoid collisions of data packets, making it more reliable for a linkage system with many devices.

There are many standards in serial communication and RS485, also known as TIA-485 (-A) or EIA-485, is just one of them. It is known for being able to be used effectively over long distances and in electrically noisy environments. Due to this and it being able to transmit data over long distances, the RS485 is used commonly as a protocol for POS, industrial and telecom.

RS485 is used in many computer and automation systems. Some of the examples are robotics, base stations, motor drives, video surveillance and also home appliances. In computer systems, RS485 is used for data transmission between the controller and a disk drive. Commercial aircraft cabins also use RS485 for low-speed data communications. 

RS485 can be seen as a mean to implement these soil moisture sensors to be used in automation systems. 

Find out more in our previous article – All about RS485 – How RS485 Works and How to Implement RS485 into Industrial Control Systems?

What is Modbus-RTU?

Modbus is the world’s most popular automation protocol in the market. Developed by Modicon, Modbus enables different devices from different manufacturers to be integrated into the main system. Most Modbus implementations use RS485 due to the allowance of longer distances, higher speeds and multiple devices on a single network.

Ref: Open4Tech

Modbus devices communicate using a Master-Slave technique where only one device (the Master) can initiate transactions (AKA queries). The other devices (the slaves) respond by giving the requested data to the master, or by taking the action requested in the query. This whole system allows manufacturing facilities to control their devices remotely and also set up automation.

Read more about it in one of our previous articles – All about RS485 – How RS485 Works and How to Implement RS485 into Industrial Control Systems?

Modbus-RTU RS485 Implementation into Soil Moisture Sensors

In the case of a Soil Moisture sensor, the sensor will be the slave in the Modbus system. With this implementation, these soil moisture sensors will be able to integrate into a Modbus system seamlessly. It will allow these soil moisture sensors to send their data collected reliably.

Wiring Diagram

Ref: Windmill

These RS485 Soil Moisture Sensors works via a 2 Wire Half Duplex System. The TX refers to the transmitted signal, and RX refers to the received signal. In the soil moisture sensor wiring diagram, the TX and RX signals share a single pair of RS485 A and B wire, limiting it to half-duplex transmission. However, it is adequate as the sensor only needs to transmit data. 

Advantages – What puts these sensors in a superior position?

There are several benefits to choosing these RS485 soil moisture sensors as opposed to other soil moisture sensors.

First, the RS485 sensors measure the dielectric constant of the soil to determine the soil moisture. This way of measuring brings several advantages by itself. It allows for excellent accuracy. It also has a long life span – being able to last for an estimated 20 years! It can be used in every kind of soils as well such as compost, landfills and soil columns.

Next, the RS485 sensors can measure temperature and some even electric conductivity as well. This will minimise the need to have multiple sensors to measure different data, which reduces the number of sensors around the agricultures. This then reduces the amount of disturbance for the agricultures.

Moving on, the RS485 implementation will allow these RS485 Soil moisture sensors to easily integrate into most automation systems. Modbus-RTU RS485 is well-known for use in many automation data systems. These RS485 soil moisture sensors will be compatible with most of them. 

Applications of RS485 Soil Moisture Sensors

These RS485 soil moisture sensors are mostly used in professional agricultural systems where every condition matters significantly. It is also used in scientific experiments with plants and environment monitoring scenarios.

Water-saving Irrigation

Source: 123RF

Being able to gauge how much water content is in the soil will take away the chances of accidental over-watering of the agriculture. Therefore, these sensors are used in many water-saving irrigation agriculture systems. With its guaranteed long life-spans and reliability, it is a much desirable choice in these systems. 

Automated Greenhouse

Source: OnRobot

The main aim of an automated greenhouse is to minimise the human care needed for the plant by automating the different processes required for the plants to grow. Monitoring of the greenhouse environment will be required for the other systems to be able to provide the appropriate amount of water, light or oxygen needed. The RS485 soil moisture will be ideal for it to integrate with the rest of the automation systems.

Horticulture and Pomology

Source: Geosciences LibreTexts

These RS485 soil moisture sensors are used in many scientific experiments with regard to horticulture and the study of pomology. These scientific experiments requires extreme precision in the data that the RS485 soil moisture sensor is able to offer. 

Summary

The Modbus-RTU RS485 Soil Moisture Sensors are a great choice if it fits your criteria. Its reliability and ease of use will ensure that you will not regret choosing it!

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