NBL-S-THR TDR Soil Moisture and Temperature Sensor

The NiuBoL NBL-S-THR is a TDR soil moisture and temperature sensor designed for continuous measurement of soil water content and soil temperature in agriculture, irrigation, greenhouses, landscaping, environmental monitoring and agricultural IoT systems.

The sensor uses TDR (Time Domain Reflectometry) technology to measure soil moisture. An electromagnetic pulse is transmitted through the probe, and the sensor analyzes the propagation response related to the apparent dielectric constant of the surrounding soil. Because soil dielectric properties change significantly with water content, this response can be converted into a soil moisture value.

The NBL-S-THR measures two parameters: soil moisture and soil temperature. It does not provide separate soil EC, salinity, pH or NPK measurement channels.

Depending on the selected version, output options include RS485 Modbus RTU, 4–20 mA and 0–5 V, allowing the sensor to connect to data loggers, PLCs, RTUs, irrigation controllers and IoT gateways.

NBL-S-THR Technical Specifications

What Does the NBL-S-THR Measure?

The NBL-S-THR provides two independent soil measurements from one probe.

Soil Moisture

Soil moisture indicates the amount of water present in the soil around the probe. Continuous soil moisture monitoring helps growers and irrigation systems understand whether the root zone is becoming too dry or remains sufficiently wet.

The NBL-S-THR provides a soil moisture output range of 0–100% with 0.1% resolution.

Soil Temperature

Soil temperature influences seed germination, root activity, microbial processes and plant development. The NBL-S-THR measures soil temperature from -50 to 100°C with 0.1°C resolution.

What the NBL-S-THR Does Not Measure

The NBL-S-THR is specifically designed for soil moisture and temperature monitoring. It should not be confused with multi-parameter soil sensors.

If soil EC is also required, select a soil temperature, moisture and conductivity sensor such as the NBL-S-TMC. If several parameters are required at one monitoring point, a multi-parameter soil sensor may be more suitable.

How Does a TDR Soil Moisture Sensor Work?

The NBL-S-THR uses TDR (Time Domain Reflectometry) technology to measure soil moisture.

The probe transmits an electromagnetic pulse through the sensing structure and measures the propagation response in the surrounding soil. This response is related to the soil's apparent dielectric constant.

Water has a much higher dielectric constant than dry soil and air. As the amount of water in the soil changes, the apparent dielectric properties around the probe also change. The sensor electronics analyze this response and convert it into a soil moisture percentage.

Because TDR measurement is based on electromagnetic and dielectric characteristics rather than a consumable chemical sensing element, it is suitable for repeated measurements and long-term buried soil monitoring.

Why Use a TDR Soil Moisture Sensor?

TDR soil moisture sensing is widely used in agricultural and environmental monitoring because soil water content can be measured electrically without repeatedly collecting soil samples.

Main advantages of the NBL-S-THR include:

• Continuous soil moisture monitoring

• Integrated soil temperature measurement

• Suitable for buried field installation

• No consumable soil-moisture sensing element

• RS485 Modbus integration

• Optional 4–20 mA and 0–5 V outputs

• IP68 sealed probe

• Suitable for automated irrigation and IoT monitoring

NBL-S-THR Product Structure

The NBL-S-THR uses a sealed sensor body with stainless-steel soil probes for direct insertion or buried installation.

The IP68 sensor body allows the probe to operate in wet soil environments. Cable joints and external connectors should still be protected from mechanical damage, standing water at unsealed connections and rodents.

RS485 Modbus Communication

The RS485 version of the NBL-S-THR supports Modbus RTU and can connect to compatible PLCs, RTUs, data loggers and agricultural IoT gateways.

NBL-S-THR Modbus Registers

The RS485 version provides soil temperature and soil moisture data through Modbus registers.

For example, if the returned soil moisture register contains decimal value 272:

272 ÷ 10 = 27.2% soil moisture

4–20 mA and 0–5 V Output Options

For controllers or data-acquisition systems that do not use Modbus, analog-output versions are also available.

4–20 mA Soil Moisture Output

Soil Moisture (%) = (I - 4) ÷ 16 × 100

4–20 mA Soil Temperature Output

Temperature (°C) = (I - 4) ÷ 16 × 150 - 50

0–5 V Soil Moisture Output

Soil Moisture (%) = V ÷ 5 × 100

0–5 V Soil Temperature Output

Temperature (°C) = V ÷ 5 × 150 - 50

Note: Use the conversion formula corresponding to the actual sensor output version ordered.

How to Install the TDR Soil Moisture Sensor

Quick Field Measurement

Select a representative measurement location and avoid stones, large roots or other hard objects that can interfere with probe insertion.

Insert the probes fully into the soil and maintain close contact between the soil and the sensing rods. Avoid repeatedly moving the sensor from side to side because this can create air gaps around the probes.

Long-Term Buried Installation

For continuous monitoring, dig to the required measurement depth and insert the probe horizontally into an undisturbed soil wall.

Backfill the installation area carefully and maintain close contact between the sensor probes and the surrounding soil.

Where Should a Soil Moisture Sensor Be Installed?

The correct installation depth depends on crop root depth, soil profile and the objective of the monitoring system. There is no single installation depth suitable for every agricultural project.

Common strategies include:

• Installing one sensor in the main active root zone

• Using multiple depths for deep-rooted crops

• Installing several monitoring points across large or variable fields

• Placing sensors near representative irrigation zones

• Avoiding locations that are unusually wet or dry compared with the surrounding field

A single soil moisture sensor represents conditions mainly around its installation point. Larger fields may therefore require multiple sensors.

TDR Soil Moisture Sensor for Irrigation

One of the main applications of the NBL-S-THR is automatic or data-assisted irrigation management.

A basic control architecture can be:

NBL-S-THR → RS485 → Irrigation Controller / PLC → Valve or Pump

For remote IoT monitoring:

TDR Soil Sensor → RS485 → Data Logger → 4G / LoRaWAN / Ethernet → MQTT / HTTP → Cloud or Private Server

The soil moisture reading can be used as one input for irrigation control. However, a single universal moisture threshold should not be applied to every project.

Irrigation thresholds should consider:

• Crop type

• Growth stage

• Root depth

• Soil texture

• Field capacity

• Irrigation method

• Sensor installation depth

• Number of monitoring points

Multiple TDR Soil Sensors on One RS485 Network

Multiple RS485 NBL-S-THR sensors can share one communication bus when each sensor has a unique Modbus address.

• Assign a unique device address to every sensor.

• Use twisted-pair cable for RS485 A/B communication.

• Prefer daisy-chain wiring where practical.

• Use a suitable 12–24 V DC power supply.

• Calculate voltage drop for longer power cables.

• Use appropriate termination where required.

• Record the address, field location and installation depth of each sensor.

For larger farms, a clear naming convention such as Field A – Zone 2 – 30 cm makes later data analysis and maintenance easier.

Factors That Affect TDR Soil Moisture Readings

Measurement quality depends on both the sensor and the soil environment.

Applications of the NBL-S-THR

• Precision irrigation

• Drip irrigation

• Smart agriculture

• Greenhouses

• Vegetable production

• Fruit orchards

• Grassland and pasture monitoring

• Landscaping and parks

• Forestry

• Soil research

• Environmental monitoring

• Agricultural IoT projects

When Should You Choose NBL-S-THR?

The NBL-S-THR is suitable when:

• You need TDR soil moisture measurement.

• You also need soil temperature from the same probe.

• You need an IP68 sensor for long-term field installation.

• You need RS485 Modbus integration with a PLC or data logger.

• You require 4–20 mA or 0–5 V instead of RS485.

• You want to integrate soil moisture into an irrigation or IoT system.

• You do not require EC, pH, salinity or NPK from the same probe.

NBL-S-THR vs Other Soil Sensors

Common Installation Mistakes

• Installing the sensor beside a large stone

• Leaving air gaps around the probe

• Repeatedly moving the sensor after insertion

• Using one monitoring point to represent a highly variable field

• Installing all sensors at the same depth when several root-zone depths need to be monitored

• Placing the sensor directly beside a drip emitter without considering whether the position represents the intended root zone

• Ignoring long-distance DC voltage drop

• Using duplicate Modbus addresses

• Failing to record the installation location and depth

TDR Soil Moisture Sensor FAQ

Q1. What does the NBL-S-THR measure?

A1. It measures soil moisture and soil temperature.

Q2. Is the NBL-S-THR a TDR soil moisture sensor?

A2. Yes. The NBL-S-THR uses TDR (Time Domain Reflectometry) technology. It transmits an electromagnetic pulse through the sensing probe and analyzes the soil's dielectric response to determine soil moisture.

Q3. Does the NBL-S-THR measure soil EC?

A3. No. The NBL-S-THR does not provide an EC measurement channel. If EC is required, select a suitable EC or multi-parameter soil sensor.

Q4. What is the soil moisture measurement range?

A4. The specified soil moisture range is 0–100% with 0.1% resolution.

Q5. What is the soil moisture accuracy?

A5. The specified moisture accuracy is ±3% under the manufacturer's test conditions.

Q6. Does the sensor support RS485 Modbus?

A6. Yes. The RS485 version supports Modbus RTU communication and can connect to compatible PLCs, RTUs and data loggers.

Q7. Are 4–20 mA and 0–5 V versions available?

A7. Yes. RS485, 4–20 mA and 0–5 V output versions are available. Confirm the required interface when ordering.

Q8. Can the sensor remain buried for long-term monitoring?

A8. Yes. The IP68 probe can be installed for continuous soil monitoring when installed correctly and good soil contact is maintained.

Q9. Can several NBL-S-THR sensors connect to one data logger?

A9. Yes. Multiple RS485 sensors can share one communication bus when each sensor has a unique Modbus address and the wiring and power supply are designed correctly.

Q10. Can the sensor control irrigation automatically?

A10. The sensor provides soil moisture and temperature data. A PLC, irrigation controller or IoT platform can use the moisture reading as one input for irrigation control.

Q11. What soil moisture threshold should be used for irrigation?

A11. There is no universal threshold. The appropriate value depends on crop type, growth stage, soil texture, rooting depth, irrigation method and management strategy.

Q12. Can NBL-S-THR data be sent to our own server?

A12. Yes. The RS485 sensor can connect to a suitable data logger or IoT gateway, which can transmit the data through MQTT, HTTP or TCP depending on the selected system.

NBL-S-THR Datasheet

NBL-S-THR-Soil-temperature-and-moisture-sensors-Instruction-Manual-V4.0.pdf

Request an NBL-S-THR Quotation

For quotation and system selection, provide the required quantity, output type, cable length, installation depth, number of monitoring points and whether the sensors need to connect to a PLC, irrigation controller, data logger, LoRaWAN node or 4G gateway.

For larger irrigation or agricultural IoT projects, also provide the approximate distance between monitoring points, available power supply, required sampling interval and whether data must be sent to a cloud platform or private server.

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