SM.3 Soil moisture, temperature and conductivity sensor

Manufacturer: Nesa
Category: Meteorology – Climatology, SENSORS, Humidity Sensors, Floor

The NESA SM.3 integrates soil temperature, conductivity, and moisture measurements into a single instrument. It uses the FDR (Frequency Domain Reflectometry 70MHz) system to measure the soil's dielectric constant and, consequently, the volume of soil moisture content; for temperature, it uses a PT100 resistance temperature detector.

Measurement range: 0–100% VWC humidity, -40°C to +70°C temperature, and 0–20 mS/cm conductivity, with AISI 316L stainless steel electrodes, resistant to fertilizer corrosion, and IP68 rated. Conductivity measurement is only available with Modbus output (SM.3-C). References: SM.3-A (0–2Vdc), SM.3-B (4–20mA), and SM.3-C (RS485/Modbus). Compliant with WMO and CE standards.

Key points

Measurement range 0÷100% VWC (humidity), -40°C ÷ +70°C (temperature) and 0 – 20 mS/cm (conductivity, only with Modbus output)
Accuracy ± 3% (0-50%) in humidity, ± 0.2°C in temperature and ± 2% FS in conductivity
Response time < 1 s
Measurement area: 7 cm radius around the probe
Outputs 0÷2Vdc, 4÷20mA or RS485/Modbus
12÷24Vdc, maximum consumption 12mA ÷ 60mA
IP68, operating temperature -30 ÷ +70°C, ABS, 316L stainless steel tips, 71 x 45 x 16mm

Technical Frequently Asked Questions

What does the SM.3 measure?

This instrument integrates soil moisture (0–100% VWC), temperature (-40°C to +70°C), and conductivity (0–20 mS/cm) measurements. Moisture is measured using the FDR (Frequency Domain Reflectometry 70MHz) system, and temperature is measured with a PT100 sensor.

What outputs does the SM.3 offer?

SM.3-A with 0-2Vdc output, SM.3-B with 4-20mA output, and SM.3-C with RS485/Modbus output. All three include a 3m cable and calibration report. Conductivity measurement is only available with the Modbus output (SM.3-C).

What is the operating temperature?

-30 ÷ +70°C, with IP68 protection rating.

How do I order it?

Sensor (SM.3), output (A, B or C) and accessories (CS05, CS10 or CSxx cable of length xx m). Manufacturer's example: SM.3 A 10.

Properties

Feature	Specification
Measurement and operating principle
Measured magnitude	Soil moisture (VWC), temperature and conductivity (EC)
Measurement principle	FDR (Frequency Domain Reflectometry 70MHz)
Temperature sensor	PT100 thermistor
Temperature control	Automatic system
Measurement range, humidity (VWC)	0÷100% VWC
Accuracy, humidity (VWC)	± 3% (0-50%) ±0.03 m³/m³
Resolution (m³/m³), humidity (VWC)	<0.002 m³/m³
Measurement range, temperature	-40°C ÷ +70°C
Accuracy, temperature	± 0.2°C
Resolution, temperature	<0.05°C
Measurement range, conductivity (EC)	0 – 20 mS/cm
Accuracy, conductivity (EC)	± 2% FS
Resolution, conductivity (EC)	<0.001mS/cm
Availability of conductivity (EC)	Only with Modbus output (SM.3-C)
Response time	< 1 s
Area of measurement	7 cm radius around the probe
Calibration	It comes with a calibration report
Exit signals
Exit sign	0÷2Vdc (SM.3-A); 4÷20mA (SM.3-B); RS485/Modbus (SM.3-C)
Power supply, environment, and mechanical data
Feeding	12÷24Vdc
Maximum consumption	12mA ÷ 60mA
Operating temperature	-30 to +70°C
Degree of protection	IP68
Building material	ABS
Probe tips	316L Stainless Steel
Dimensions	71 x 45 x 16mm (tips Ø4 x 55mm; see drawing)
Cable length	3 m
Standard	WMO
Regulatory compliance	EC

Reference	Configuration
SM.3-ASM3A	Output: 0–2Vdc; Supply: 0–100% VWC, -40–+70°C; with 3m cable calibration report
SM.3-BSM3B	Output: 4÷20mA · Supply: 0÷100% VWC, -40 ÷ +70°C; with 3m cable calibration report
SM.3-CSM3C	Output: RS485/Modbus · Supply: 0÷100% VWC, -40 ÷ +70°C, 0÷20ms; with 3m cable calibration report