SX-HEC20

SIGNUX HEC20

Soil moisture, conductivity and temperature probe

Direct-insertion probe that measures volumetric moisture, electrical conductivity and soil temperature. Plastic body sealed in epoxy resin with stainless steel rods, made to stay buried.

The sensor can be calibrated for different soil types, whether in research, irrigation, greenhouses, smart agriculture, among other fields.

Measures: Moisture · Conductivity · Temperature
Output: 4-20 mAVoltage
Protection: IP68
Operating: -40 to +85 °C

HEC20 probe on a white background: white rectangular body with cable and three steel rods

What sets it apart

Three parameters at a single point

Moisture, conductivity, and temperature measured in the same soil volume—without the need for three separate installations or boreholes.

Waterproof, IP68

Sealed in epoxy resin with stainless steel rods. Bury it and forget it: it needs no manhole or watertight box.

Low sensitivity to salinity

The moisture reading holds up in saline soils, where ordinary capacitive probes drift.

Multiple integration options

RS485 with Modbus RTU, or analogue output as 0-2 V voltage or 4-20 mA current. No intermediate platform.

Protected against installation mistakes

Reverse-polarity protection and built-in TVS/ESD suppressors, which is what fails in the field.

Calibratable for your soil

Supports soil-specific calibration when the texture strays from the factory default.

Configurations

Cable length	Connector / output	Part number
2 m	Pigtail	SX-HEC20-2M-PT
2 m	M10 connector	SX-HEC20-2M-M10
4 m	Pigtail	SX-HEC20-4M-PT
4 m	M10 connector	SX-HEC20-4M-M10

Specifications

General

Measured quantities: Moisture · Conductivity · Temperature
Family: Direct-insertion probe
Output: RS485 · 4-20 mA · Voltage
Rods: 3 pcs

Temperature

Range: -40 to +80 °C
Resolution: 0,1 °C
Accuracy: ±0,5 °C

Soil moisture

Measuring principle: FDRFrequency-domain reflectometry
Range L: 0-50 / 0-100 %Depending on the ordered configuration
Resolution: 0,03 %In the 0-50 % section
Range H: 0-100 %Depending on the ordered configuration
Resolution: ±2 %In the 0-100 % section
Accuracy: 1 %In the 0-50 % section
±3 %In the 50-100 % section

Electrical conductivity EC

Measuring principle: AC excitation
Range: 0-5000 / 0-10000 / 0-20000 µS/cmDepending on the ordered configuration
Resolution: 10 µS/cmUp to 10,000 µS/cm
50 µS/cmFrom 10,000 to 20,000 µS/cm
Accuracy: ±3 %Up to 10,000 µS/cm
±5 %From 10,000 to 20,000 µS/cm
Temperature compensation: 0-50 °C

Output and power

Output interface: RS485 Modbus RTU / 0-2 V / 4-20 mADepending on the ordered configuration
Power supply: 3,9-30 VDCRS485 or voltage output
Power supply: 12-30 VDCRequired with 4-20 mA output
Consumption: 6 mAAt 12 V DC, RS485 or voltage output
Consumption: 10 mAAt 12 V DC, 4-20 mA output
Protocol: Modbus RTUFunctions 3, 4, 6 and 16
Factory defaults: 9600 8N1, address 1Recoverable via the SET wire if lost

Construction

Protection rating: IP68
Operating temperature: -40 to +85 °C
Rods: Stainless steel
Sealing: Epoxy resin
Installation: Surface or buried
Cable length: 2 mOther lengths on request
Dimensions: 88 × 26 × 71 mm18 mm tall body and 53 mm rods, per the dimensioned drawing

Manual

1Introduction

The SX-HEC20 measures soil moisture content, electrical conductivity (EC) and temperature. It has a resin-sealed plastic body and sensing rods that can be inserted directly into the soil, offering long-term stability. The soil moisture output signal can be RS485, analogue voltage or analogue current. It can also be calibrated for specific soil types.

The sensor is suitable for scientific research, irrigation, greenhouses, smart agriculture, among other applications.

•Integrated soil moisture, electrical conductivity (EC) and temperature measurements
•Output interface: RS485, voltage and current
•Low sensitivity to salinity
•Minimal soil disturbance
•IP68 protection rating (waterproof); suitable for direct burial in soil
•High accuracy and excellent stability
•Reverse-polarity protection and built-in TVS/ESD protection

Specifications

Output Interface	Analog Voltage	Analog Current 4-20mA	RS485 Modbus
Power Supply	3.9-30 VDC	12-30 VDC	3.9-30 VDC
Consumption	6mA@12 VDC	10mA@12 VDC	6mA@12 VDC
Soil Moisture Measurement	Range:0-50%,0-100% Resolution:0-50%:0.03%,50-100%:1% Accuracy:0-50%:2%,50-100%:3%
EC Measurement	Range: 0-5000us/cm, 10000us/cm, 20000us/cm Resolution: 0-10000us/cm, 10us/cm; 10000-20000us/cm, Accuracy: 0-10000us/cm, ±3%; 10000-20000us/cm, ±5% 50us/cm EC temperature compensation: 0-50°C
Temperature Measurement	Range: -40~80°C Resolution:0.1°C Accuracy:±0.5°C
Measurement Technique	Moisture by FDR and EC by AC excitation
IP Ratings	IP68
Operating Temperature	-40~85°C
Sensor Rod	Stainless steel
Sensor Sealed	Epoxy resin
Installation	Surface or buried installation
Cable Length	2 meters or Customize
Dimension	882671mm

Figure from the manufacturer's manual, page 1

2Wiring diagram

Type	Wiring diagram
Analog Voltage Output	Red (V+): Power Supply + Black (G): Power Supply - Blue (O1): Analog Output (Can be set to VWC, EC, Temperature in factory) Brown (O2): Analog Output (Can be set to VWC, EC, Temperature in factory)

Figure from the manufacturer's manual, page 5

Analog Current Output

Red (V+): Power Supply + Black (G): Power Supply - Blue (O1): Analog Output (Can be set to VWC, EC, Temperature in factory) Brown (O2): Analog Output (Can be set to VWC, EC, Temperature in factory)

RS485 Modbus	Red (V+): Power Supply + Black (G): Power Supply - Yellow (T+): RS485+/A/T+ White (T-): RS485-/B/T- Green (SET):
	SETTING mode. When sensor power-up with the SET wire connected toPowerSupply +, then sensor using setting mode communication parameters for RS485. When sensor power-up with the SET wire connected to Power Supply–or unconnected , the sensor using communication parameters in register for RS485. Please refer to the usage below.

Figure from the manufacturer's manual, page 6

ALL RS485 communication parameters (Modbus Slave Address, baudrate, parity, databits, stopbits) are set in internal register and can be saved when power down, the factory setting is ADDRESS=1, BAUDRATE=9600bps,PARITY=NONE, DATABITS=8bits, STOPBITS=1bit; Sometimes you may FORGET the communication settings, In this case, you can connect the GREEN & RED wire together to PowerSupply+, black wire to PowerSupply-, then re-power up the sensor, then the sensor start-up with a fixed communication settings(we call it setting mode) ADDRESS=0, BAUDRATE=9600bps,PARITY=NONE, DATABITS=8bits, STOPBITS=1bit; Communicate with the sensor using this parameters and then set your desired communication parameters, then disconnect the green wire from PowerSupply+, then re-power up the sensor, and the sensor will communicate with your settings.

3Dimensions and ordering information

3.1Dimensions

Figure from the manufacturer's manual, page 7

3.2Ordering Information

Parameters	Code	Comments
Code 1: Product Series	SX-HEC20	Soil Moisture, EC, Temperature Sensor
Code 2: Measuring_Parameters	A B C	Soil Moisture, EC, Temperature (Supported Output Interface: RS485) Soil Moisture, EC (Supported Output Interface: RS485 and Analog Voltage, Analog Current) EC, Temperature (Supported Output Interface: RS485 and Analog Voltage, Analog Current)
Code 3: Moisture Range	A B	0-50% 0-100%
Code 4: EC Range	A B C	0-5000us/cm 0-10000us/cm 0-20000us/cm
Code 5: Power Supply	A B D	3.9-30 VDC (not applicable for 4-20mA output) 12-30 VDC (applicable for 4-20mA output) Customize
Code 6: Output Interface	A B C D E	Analog Voltage 0-2V Analog Current 4-20mA (Power Supply >12 VDC) RS485,Modbus-RTU RS485,Modbus-RTU & Analog Voltage 0-2V RS485,Modbus-RTU & Analog Current 4-20mA (Power Supply >12 VDC)
Code 7: Cable Length	002 XXX	2 meters XXX is required cable length(Unit: meter)

Ordering Code Example: SX-HEC20 - A B C A C 002

Product Series: SX-HEC20 Soil Moisture, EC, Temperature Sensor;

Measuring Parameters: Soil Moisture, EC, Temperature;

Moisture Range: 0-100%;

EC Range: 0-20000us/cm;

Power Supply: 3.9-30 VDC;

Output Interface: RS485, Modbus-RTU;

Cable Length: 2 meters;

4Safety, care and installation

4.1Safety and care

•The rods of the Sensor are sharp for ease insertion. Care must be taken and handling precautions followed.
•Avoid touching the rods or exposing them to other sources of static damage, particularly when powered up.
•Do not pull the sensor out of the soil by its cable.
•If you feel any resistance when inserting the sensor into soil, it is likely you have encountered a stone. Stop pushing and re-insert at a new location.

4.2Installation

•Surface installation Clear away any stones. Pre-form holes in very hard soils before insertion.
•Push the sensor into the soil until the rods are fully inserted. Ensure good soil contact.
•If you feel strong resistance when inserting the sensor, you have probably hit a stone. Stop, and re-insert at a new location.

Note: The sensor is suitable for soil surface temperature measurements.

Installing at depth

•Make a 45mm diameter hole, preferably at about 10° to the vertical using a auger.
•Push the sensor into the soil until rods are fully inserted. Ensure good soil contact.
•Fill and repack the hole with soil.

Alternatively

•Dig a trench, and install horizontally.

5Output signal conversion

Output Interface	Parameters Range	Conversion Formula
Analog Voltage Output 0-2V	Temperature: -40-80°C	TEMP=60.0* VOLTAGE-40. When VOLTAGE=1.0V,then TEMP=60.0* 1.0-40=20.00°C
	VWC: 0-50%	VWC=25VOLTAGE. When VOLTAGE=0.3V,then VWC=250.3=7.5%
	VWC: 0-100%	VWC =50* VOLTAGE. When VOLTAGE=0.3V,then VWC =50*0.3=15%
	EC: 0-5000us/cm	EC=2500VOLTAGE. When VOLTAGE=0.3V,then EC=25000.3=750us/cm.
	EC: 0-10000us/cm	EC =5000* VOLTAGE. When VOLTAGE=0.3V,then EC=5000*0.3=1500us/cm
	EC: 0-20000us/cm	EC =10000* VOLTAGE. When VOLTAGE=0.3V,then EC=10000*0.3=3000us/cm.
Analog Current Output 4-20mA	Temperature: -40-80°C	TEMP=7.5CURRENT-70. When CURRENT=10mA, then TEMP=7.510-70=5.00°C.
	VWC: 0-50%	VWC= 3.125 ( CURRENT -4). When CURRENT=6.4mA, then VWC= 3.125(6.4-4)=7.50%
	VWC: 0-100%	VWC = 6.25 ( CURRENT -4). When CURRENT=6.4mA, then VWC=6.25(6.4-4)=15%
	EC: 0-5000us/cm	EC = 312.50 ( CURRENT -4). When CURRENT=6.4mA, then EC= 312.50(6.4-4)=750us/cm
	EC: 0-10000us/cm	EC = 625 ( CURRENT -4). When CURRENT=6.4mA, then EC=625(6.4-4)=1500us/cm
	EC: 0-20000us/cm	EC = 1250 ( CURRENT -4). When CURRENT=6.4mA, then EC=1250(6.4-4)=3000us/cm
RS485 Modbus-RTU	Temperature: -40-80°C	TEMP=(REGISTER VALUE)/100. When REGISTERVALUE=2013, then TEMP= 2013/100=20.13°C.
	VWC for all ranges	VWC=(REGISTER VALUE)/100. When REGISTERVALUE=2013, then VWC= 2013/100=20.13%.
	EC for all ranges	EC=(REGISTER VALUE). When REGISTERVALUE=1568, then EC= 1568us/cm.
Customize	Contact support for customized sensor interface

NOTE: The unit of VOLTAGE is (V), The unit of CURRENT is (mA).

NOTE: VWC is Volumetric Water Content, EC is Electrical Conductivity.

6RS485 Modbus protocol

6.1Modbus protocol

Modbus Protocol is widely used to establish master-slave communication between intelligent devices or sensors. A MODBUS message sent from a master to a slave contains the address of the slave, the function code (e.g. 'read register’ or 'write register’), the data, and a check sum (LRC or CRC).
The sensor is RS485 interface with Modbus protocol. The default serial communication settings is slave address 1, modbus rtu, 9600bps, 8 databits and 1 stop bit. All communication settings can be changed with modbus command, and take effective after re-power up the sensor.

Following modbus function code are supported by sensor.

•Modbus Function Code 0x03 : used for reading holding register.
•Modbus Function Code 0x04 : used for reading input register.
•Modbus Function Code 0x06 : used for writing single holding register.
•Modbus Function Code 0x10: used for writing multiple holding register.

6.2Modbus registers

Parameters	Register Addr. (HEX/DEC)	Data Type	Modbus Function Code(DEC)	Range and Comments	Default Value
TEMPERATURE	0x0000/0	INT16 RO	3/4	-4000-8000 for -40.00~80.00°C	N/A
VWC-Volumetric Water Content	0x0001/1	UINT16 RO	3/4	0-10000 for 0-100%	N/A
EC-Electrical Conductivity	0x0002/2	UINT16 RO	3/4	0-20000 for 0-20000us/cm	N/A
SALINITY	0x0003/3	UINT16 RO	3/4	0-20000 for 0-20000mg/L	N/A
TDS	0x0004/4	UINT16 RO	3/4	0-20000 for 0-20000mg/L	N/A
EPSILON	0x0005/5	UINT16 RO	3/4	0-30000 for 0.00-300.00	N/A
RESERVED	0x0006/6	UINT16 RO	3/4	N/A	0
VWC_RAWAD	0x0007/7	UINT16 RO	3/4	0-4096 for 0-4096	N/A
RESERVED	0x0008/8	UINT16 RO	3/4	N/A	0
POREEC	0x0009/9	UINT16 RO	3/4	0-32000 for 0-32000us/cm	N/A

SOILTYPE	0x0020/32	UINT16 R/W	3/6/16	0-5 0:Mineral 1:Sand 2:Clay 3:Organic 4:User Defined Curve 5:Soilless(Rockwool, etc)	0:Mineral
TEMPUNIT	0x0021/33	UINT16 R/W	3/6/16	0:°C 1:°F	0
ECTEMPCOFF	0x0022/34	UINT16 R/W	3/6/16	0-100 for 0.0%-10.0%	20(2%)
SALINITYCOFF	0x0023/35	UINT16 R/W	3/6/16	0-100 for 0.00-1.00	55(0.55)
TDSCOFF	0x0024/36	UINT16 R/W	3/6/16	0-100 for 0.00-1.00	50(0.5)
MEASURE METHOD	0x0025/37	UINT16 R/W	3/6/16	0: Continuous Meas. 1: Request Meas.	1
EPSILON OFFSET	0x0026/38	UINT16 R/W	3/6/16	Epsilon Value when Substrate VWC is 0% 0-200 for 0-20.00	58(5.8)

SLAVEADDRESS	0x0200/512	UINT16 R/W	3/6/16	0-255	1
BAUDRATE	0x0201/513	UINT16 R/W	3/6/16	0-6 0:1200bps 1:2400bps 2:4800bps 3:9600bps 4:19200bps 5:38400bps	3:9600bps
PROTOCOL	0x0202/514	UINT16 R/W	3/6/16	0-1 0:Modbus RTU 1:Modbus ASCii	0:Modbus RTU
PARITY	0x0203/515	UINT16 R/W	3/6/16	0-2 0:None 1:Even 2:Odd	0:None Parity
DATABITS	0x0204/516	UINT16 R/W	3/6/16	1 1:8 databits	1:8 databits
STOPBITS	0x0205/517	UINT16 R/W	3/6/16	0-1 0:1 stopbit 1:2 stopbits	0:1 stopbit
RESPONSE DELAY	0x0206/518	UINT16 R/W	3/6/16	0-255 for 0-2550 milliseconds	0
ACTIVEOUTPUT INTERVAL	0x0207/519	UINT16 R/W	3/6/16	0-255 for 0-255 seconds	0

4-byte floating point WITH THE LOW WORD FIRST (CDAB order). The manufacturer calls these «FLOAT», but measured on a real unit they are NOT standard IEEE 754: for that, use the 0x1100 block below.

Parameters	Register Addr. (HEX/DEC)	Data Type	Modbus Function Code(DEC)	Range and Comments	Default Value
TEMPERATURE FLOAT	0x1000/4096	FLOAT RO	3/4	-40.00-80.00 (°C)	N/A
VWC_FLOAT	0x1002/4098	FLOAT RO	3/4	0.00-100.00 (%)	N/A
EC_FLOAT	0x1004/4100	FLOAT RO	3/4	0-20000 (us/cm)	N/A
SALINITY FLOAT	0x1006/4102	FLOAT RO	3/4	0-20000(mg/L)	N/A
TDS_FLOAT	0x1008/4104	FLOAT RO	3/4	0-20000(mg/L)	N/A
EPSILON FLOAT	0x100A/4106	FLOAT RO	3/4	0.00-300.00	N/A
RESERVED FLOAT	0x100C/4108	FLOAT RO	3/4	RESERVED	0
VWC_RAWAD FLOAT	0x100E/4110	FLOAT RO	3/4	0.00-4096.00	N/A
RESERVED FLOAT	0x1010/4112	FLOAT RO	3/4	RESERVED	0
POREEC FLOAT	0x1012/4114	FLOAT RO	3/4	0-32000 (us/cm)	N/A
RESERVED FLOAT	0x1014/4116	FLOAT RO	3/4	RESERVED	0
RESERVED FLOAT	0x1016/4118	FLOAT RO	3/4	RESERVED	0
RESERVED FLOAT	0x1018/4120	FLOAT RO	3/4	RESERVED	0
RESERVED FLOAT	0x101A/4122	FLOAT RO	3/4	RESERVED	0
RESERVED FLOAT	0x101C/4124	FLOAT RO	3/4	RESERVED	0
RESERVED FLOAT	0x101E/4126	FLOAT RO	3/4	RESERVED	0

4-byte floating point in STANDARD IEEE 754 (ABCD order). The manufacturer calls these «FLOAT INVERSE», but these are the ones a PLC or a gateway expects. Measured on a real unit.

Parameters	Register Addr. (HEX/DEC)	Data Type	Modbus Function Code(DEC)	Range and Comments	Default Value
TEMPERATURE FLOAT_INVERSE	0x1100/4352	FLOAT_INVERSE RO	3/4	-40.00-80.00 (°C)	N/A
VWC_FLOAT_INVERSE	0x1102/4354	FLOAT_INVERSE RO	3/4	0.00-100.00 (%)	N/A
EC_FLOAT_INVERSE	0x1104/4356	FLOAT_INVERSE RO	3/4	0-20000 (us/cm)	N/A
SALINITY FLOAT_INVERSE	0x1106/4358	FLOAT_INVERSE RO	3/4	0-20000(mg/L)	N/A
TDS_FLOAT_INVERSE	0x1108/4360	FLOAT_INVERSE RO	3/4	0-20000(mg/L)	N/A
EPSILON FLOAT_INVERSE	0x110A/4362	FLOAT_INVERSE RO	3/4	0.00-300.00	N/A
RESERVED FLOAT_INVERSE	0x110C/4364	FLOAT_INVERSE RO	3/4	RESERVED	0
VWC_RAWAD FLOAT_INVERSE	0x110E/4366	FLOAT_INVERSE RO	3/4	0.00-4096.00	N/A
RESERVED FLOAT_INVERSE	0x1110/4368	FLOAT_INVERSE RO	3/4	RESERVED	0
POREEC FLOAT_INVERSE	0x1112/4370	FLOAT_INVERSE RO	3/4	0-32000 (us/cm)	N/A
RESERVED FLOAT_INVERSE	0x1114/4372	FLOAT_INVERSE RO	3/4	RESERVED	0
RESERVED FLOAT_INVERSE	0x1116/4374	FLOAT_INVERSE RO	3/4	RESERVED	0
RESERVED FLOAT_INVERSE	0x1118/4376	FLOAT_INVERSE RO	3/4	RESERVED	0
RESERVED FLOAT_INVERSE	0x111A/4378	FLOAT_INVERSE RO	3/4	RESERVED	0
RESERVED FLOAT_INVERSE	0x111C/4380	FLOAT_INVERSE RO	3/4	RESERVED	0
RESERVED FLOAT_INVERSE	0x111E/4382	FLOAT_INVERSE RO	3/4	RESERVED	0

The following registers' value are the same with register 0x0000-0x0009, just the re-order of those register.

Parameters	Register Addr. (HEX/DEC)	Data Type	Modbus Function Code(DEC)	Range and Comments	Default Value
TEMPRATURE	0x1200/4608	INT16 RO	3/4	-4000-8000 for -40.00~80.00°C	N/A
VWC	0x1201/4609	UINT16 RO	3/4	0-10000 for 0-100%	N/A
EC	0x1202/4610	UINT16 RO	3/4	0-20000 for 0-20000us/cm	N/A
POREEC	0x1203/4611	UINT16 RO	3/4	0-32000 for 0-32000us/cm	N/A
EPSILON	0x1204/4612	UINT16 RO	3/4	0-30000 for 0.00~300.00	N/A
SALINITY	0x1205/4613	UINT16 RO	3/4	0-20000 for 0-20000mg/L	N/A
TDS	0x1206/4614	UINT16 RO	3/4	0-20000 for 0-20000mg/L	N/A
RESERVED	0x1207/4615	UINT16 RO	3/4	N/A	0
VWC_RAWAD	0x1208/4616	UINT16 RO	3/4	0-4096 for 0-4096	N/A
RESERVED	0x1209/4617	UINT16 RO	3/4	N/A	0

UINT16:16 bit unsigned integer
INT16:16bit signed integer
RO: Register is Read Only
R/W: Register is Read/Write
HEX: Hexadecimal (data with 0x/0X prefix)
DEC: Decimal
FLOAT: If IEEE754 little-endian byte order is [A,B,C,D], the FLOAT format is [B,A,D,C]
FLOAT_INVERSE: If IEEE754 little-endian byte order is [A,B,C,D], the FLOAT_INVERSE format is [D,C,B,A]

6.3Detailed description of Modbus registers

TEMPERATURE — Temperature Value
Data Range	-4000-8000 For -40.00~80.00(°C)	Default: N/A
Parameter Storage	N/A

Note: Temperature value (Binary complement).
Example: When REGISTER = 0x0702 (HEX format), then
VALUE=(0x07*256+0x02)/100=17.94°C. When REGISTER=FF05H (HEX format), then
VALUE=((0xFF*256+0x05)-0xFFFF-0x01)/100 =(0xFF05-0xFFFF-0x01)/100=-2.51°C.

TEMPERATURE_FLOAT — Temperature Value, FLOAT Format TEMPERATURE_FLOAT_INVERSE — Temperature Value, FLOAT_INVERSE Format
Data Range	-40.00-80.00	Default: N/A
Parameter Storage	N/A

VWC — Volmetric Water Content
Data Range	0-10000 For 0-100%	Default: N/A
Parameter Storage	N/A

Note: Volmetric Water Content value.
Example: When REGISTER = 0x0702 (HEX format), then VALUE=(0x07*256+0x02)/100=17.94%

VWC_FLOAT — Volmetric Water Content, FLOAT Format VWC_FLOAT_INVERSE — Volmetric Water Content, FLOAT_INVERSE Format
Data Range	0.00-100.00 (%)	Default: N/A
Parameter Storage	N/A

Note: Volmetric Water Content value.

EC — Electrical Conductivity
Data Range	0-20000 For 0-20000 (us/cm)	Default: N/A
Parameter Storage	N/A

Note: Electrical Conductivity.
Example: When REGISTER = 0x0702 (HEX format), then VALUE=(0x07*256+0x02)=1794us/cm

EC_FLOAT — Electrical Conductivity, FLOAT Format EC_FLOAT_INVERSE — Electrical Conductivity, FLOAT_INVERSE Format
Data Range	0-20000 (us/cm)	Default: N/A
Parameter Storage	N/A

Note: Electrical Conductivity.

SALINITY — Salinity
Data Range	0-20000 For 0-20000 (mg/L)	Default: N/A
Parameter Storage	N/A

Note: Salinity
Example: When REGISTER = 0x0702 (HEX format), then VALUE=(0x07*256+0x02)=1794mg/L.
Salinity is derived by EC, SALINITY=EC*SALINITYCOFF, in which SALINITYCOFF is a coefficient, please refer to SALINITYCOFF.

SALINITY_FLOAT — Salinity, FLOAT Format SALINITY_FLOAT_INVERSE — Salinity, FLOAT_INVERSE Format
Data Range	0-20000 (mg/L)	Default: N/A
Parameter Storage	N/A

Note: Salinity

TDS — Total Dissolved Solid
Data Range	0-20000 For 0-20000 (mg/L)	Default: N/A
Parameter Storage	N/A

Note: Total Dissolved Solid
Example: When REGISTER = 0x0702 (HEX format), then VALUE=(0x07*256+0x02)=1794mg/L.
TDS is derived by EC, TDS=EC*TDSCOFF, in which TDSCOFF is a coefficient, please refer to TDSCOFF.

TDS_FLOAT — Total Dissolved Solid, FLOAT Format TDS_FLOAT_INVERSE — Total Dissolved Solid, FLOAT_INVERSE Format
Data Range	0-20000 (mg/L)	Default: N/A
Parameter Storage	N/A

Note: Total Dissolved Solid

EPSILON — Epsilon
Data Range	0-30000 for 0.00-300.00	Default: N/A
Parameter Storage	N/A

Note: Epsilon
Example: When REGISTER = 0x0702 (HEX format), then VALUE=(0x07*256+0x02)/100=17.94.
VWC is derived by EPSILON, VWC is a function of EPSILON. This value is always used for self calibration usage.

EPSILON_FLOAT — Epsilon, FLOAT Format EPSILON_FLOAT_INVERSE — Epsilon, FLOAT_INVERSE Format
Data Range	0.00-300.00	Default: N/A
Parameter Storage	N/A

Note: Epsilon

VWC_RAWAD — VWC Raw AD
Data Range	0-4096 for 0-4096	Default: N/A
Parameter Storage	N/A

Note: Water Content Raw AD value

VWC_RAWAD_FLOAT — VWC Raw AD, FLOAT Format VWC_RAWAD_FLOAT_INVERSE — VWC Raw AD, FLOAT_INVERSE Format
Data Range	0-4096.00	Default: N/A
Parameter Storage	N/A

Note: Water Content Raw AD value

POREEC_RAWAD — Pore EC
Data Range	0-32000 (us/cm)	Default: N/A
Parameter Storage	N/A

Note: Pore EC

POREEC_FLOAT — Pore EC, FLOAT Format POREEC_FLOAT_INVERSE — Pore EC, FLOAT_INVERSE Format
Data Range	0-32000 (us/cm)	Default: N/A
Parameter Storage	N/A

Note: Pore EC

SOILTYPE — Soil Type
Data Range	0-5 0:Mineral 1:Sand 2:Clay 3:Organic 4:User Defined Curve 5:Soilless(Rockwool, etc)	Default: 0:Mineral
Parameter Storage	YES

Note: Soil Type.

TEMPUNIT — Temperature Unit
Data Range	0:°C 1:°F	Default: 0
Parameter Storage	YES

Note: Temperature Unit.

ECTEMPCOFF — EC Temperature Compensation Coefficient
Data Range	0-100 for 0.0%-10.0%	Default: 20(2%)
Parameter Storage	YES

Note: EC Temperature Compensation Coefficient

SALINITYCOFF — Salinity Coefficient
Data Range	0-100 for 0.00-1.00	Default: 55(0.55)
Parameter Storage	YES

Note: Salinity Coefficient.

TDSCOFF — TDS Coefficient
Data Range	0-100 for 0.00-1.00	Default: 50(0.50)
Parameter Storage	YES

Note: TDS Coefficient.

MEASUREMETHOD — Measure Method
Data Range	0: Continuous 1: Request	Default: 1
Parameter Storage	YES

Note: In Continuous mode, the sensor always convert the VWC, EC and Temperature and update the internal data and ready for reading. In Request mode, the sensor convert the VWC, EC and Temperature data by receiving the data request command from master device.

EPSILON_OFFSET — Epsilon Offset
Data Range	0-200 for 0-20.00	Default: 58(5.8)
Parameter Storage	YES

Note: Epsilon Value when Substrate VWC is 0%

SLAVEADDRESS — Serial Comm Slave Address
Data Range	0-255	Default: 1
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.

BAUDRATE — Serial Comm Baudrate
Data Range	0-5 0:1200bps 1:2400bps 2:4800bps 3:9600bps 4:19200bps 5:38400bps	Default: 3
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.

PROTOCOL — Serial Comm Protocol
Data Range	0-1 0:Modbus RTU 1:Modbus ASCii	Default: 0
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.

PARITY — Serial Comm Parity
Data Range	0-2 0:NONE 1:EVEN 2:ODD	Default: 0
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.

DATABITS — Serial Comm Databits
Data Range	1:8 databits	Default: 1
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.

STOPBITS — Serial Comm Stopbits
Data Range	0-1 0:1 stopbit 1:2 stopbits	Default: 0
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.

RESPONSEDELAY — Serial Comm Response Delay
Data Range	0-255 for 0-2550 milliseconds, 0 for disabled	Default: 0
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.
Note: Sensor will delay a period before response to master request command.
Example: When set to 5 and receive a request from master device, then sensor will delay 5*10ms=50ms, then response to master.

ACTIVEOUTPUTINTERVAL — Serial Comm Active Output Interval time
Data Range	0-255 for 0-255 seconds, 0 for disabled
Parameter Storage	YES

Note: Please re-power on the sensor to take effective after set.
Note: Sensor will output the data actively without any master request command.
Note: Only ONE sensor should be on RS485 network, or there will be data collision and corrupt the data on line.
Note: Refer to SETTING mode to exit the Active Output Mode.
Example: When set to 5 then sensor will output the data every 5 seconds without any master request command.

6.4Modbus function codes

For description below, data started with 0X/0x means that it's in HEX format.

6.4.1Function Code 3 Protocol Example

Master Request:AA 03 RRRR NNNN CCCC |||

AA	1 byte	Slave Address, 0-255
0x03	1 byte	Function Code 3
RRRR	2 byte	Starting Register Addr
NNNN	2 byte	Quantity of Register to read
CCCC	2 byte	CRC CHECKSUM

Slave Response:AA 03 MM VV0 VV1 VV2 VV3... CCCC |||

AA	1 byte	Slave Address, 0-255
0x03	1 byte	Function Code 3
MM	1 byte	Register Data Byte Count
VV0,VV1	2 byte	Register Value (High8bits first)
VV2,VV3	2 byte	Register Value (High8bits first)
...	...	...
CCCC	2 byte	CRC CHECKSUM

Example: Read register 0x0200-0x0201, that is slave address and baudrate.

Master Request:01 03 0200 0002 C5B3 |||

Slave Addr.	1 byte	0x01
Function Code	1 byte	0x03
Starting Register Addr.	2 byte	0x0200
Quantity of Register to read	2 byte	0x0002
Checksum	2 byte	0xC5B3

Slave Response:01 03 04 00 01 00 03 EB F2 |||

Slave Addr.	1 byte	0x01
Function Code	1 byte	0x03
Register Data Byte Count	1 byte	0x04
Register Value: Address	2 byte	0x00 (HIGH 8 Bits) 0x01 (LOW 8 Bits)
Register Value: Baudrate	2 byte	0x00 (HIGH 8 Bits) 0x03 (LOW 8 Bits)
Checksum	2 byte	0xEB F2

6.4.2Function code 4 – protocol example

Master Request:AA 04 RRRR NNNN CCCC |||

Master Request:AA 04 RRRR NNNN CCCC
AA	1 byte	Slave Address, 0-255
0x04	1 byte	Function Code 4
RRRR	2 byte	Starting Register Addr
NNNN	2 byte	Quantity of Register to read
CCCC	2 byte	CRC CHECKSUM

Slave Response:AA 04 MM VV0 VV1 VV2 VV3... CCCC |||

Slave Response:AA 04 MM VV0 VV1 VV2 VV3... CCCC
AA	1 byte	Slave Address, 0-255
0x04	1 byte	Function Code 4
MM	1 byte	Register Data Byte Count
VV0,VV1	2 byte	Register Value (High8bits first)
VV2,VV3	2 byte	Register Value (High8bits first)
...	...	...
CCCC	2 byte	CRC CHECKSUM

Example: Read register 0x0000-0x0002, that is temperature, soil moisture, and EC.
Slave Addr.	1 byte	0x01
Function Code	1 byte	0x04
Starting Register Addr.	2 byte	0x0000
Quantity of Register to read	2 byte	0x0003
Checksum	2 byte	0xB00B

Master Request:01 04 0000 0003 B00B |||

Slave Addr.	1 byte	0x01
Function Code	1 byte	0x04
Starting Register Addr.	2 byte	0x0000
Quantity of Register to read	2 byte	0x0003
Checksum	2 byte	0xB00B

Slave Response:01 04 06 08 90 0E 93 02 4E D2 57 |||

Slave Response:01 04 06 08 90 0E 93 02 4E D2 57
Slave Addr.	1 byte	0x01
Function Code	1 byte	0x04
Register Data Byte Count	1 byte	0x06
Register Value: Temperature	2 byte	0x08 90
Register Value: Soil Moisture	2 byte	0x0E 93
Register Value: EC	2 byte	0x02 4E
Checksum	2 byte	0xD2 57

Temperature = (0x08*256+0x90)/100 = 2192/100 = 21.92 °C Soil Moisture = (0x0E*256+0x93)/100 = 3731/100 = 37.31% EC = 0x02*256+0x4E = 2*256+78 = 590 us/cm

6.4.3Function code 6 – protocol example

Master Request:AA 06 RRRR VVVV CCCC |||

Master Request:AA 06 RRRR VVVV CCCC
AA	1 byte	Slave Address, 0-255
0x06	1 byte	Function Code 6
RRRR	2 byte	Register Addr (High8bits first)
VVVV	2 byte	Register Value (High8bits first)
CCCC	2 byte	CRC CHECKSUM

Slave Response:AA 06 RRRR VVVV CCCC |||

Slave Response:AA 06 RRRR VVVV CCCC
AA	1 byte	Slave Address, 0-255
0x06	1 byte	Function Code 6
RRRR	2 byte	Register Addr (High8bits first)
VVVV	2 byte	Register Value (High8bits first)
CCCC	2 byte	CRC CHECKSUM

Example: Write Register 0x0021, that is set temperature unit to °F.
Slave Addr.	1 byte	0x01
Function Code	1 byte	0x06
Register Addr.	2 byte	0x0021 (High8bits first)
Register Value	2 byte	0x0001 (High8bits first)
Checksum	2 byte	0x1800

Master Request:01 06 0021 0001 1800 |||

Slave Addr.	1 byte	0x01
Function Code	1 byte	0x06
Register Addr.	2 byte	0x0021 (High8bits first)
Register Value	2 byte	0x0001 (High8bits first)
Checksum	2 byte	0x1800

Response:01 06 0021 0001 1800 |||

Response:01 06 0021 0001 1800
Slave Addr.	1 byte	0x01
Function Code	1 byte	0x06
Register Addr.	2 byte	0x0021 (High8bits first)
Register Value	2 byte	0x0001 (High8bits first)
Checksum	2 byte	0x1800

6.4.4Function code 16 – protocol example

Master Request:AA 10 RRRR NNNN MM VVVV1 VVVV2 ...CCCC |||

Master Request:AA 10 RRRR NNNN MM VVVV1 VVVV2 ...CCCC
AA	1 byte	Slave Address, 0-255
0x10	1 byte	Function Code 0x10
RRRR	2 byte	Starting Register Addr
NNNN	2 byte	Quantity of Register to write
MM	1 byte	Register Data Byte Count
VVVV1	2 byte	Register Value (High8bits first)
VVVV2	2 byte	Register Value (High8bits first)
...	...	...
CCCC	2 byte	CRC CHECKSUM

Slave Response:AA 10 RRRR NNNN CCCC |||

Slave Response:AA 10 RRRR NNNN CCCC
AA	1 byte	Slave Address, 0-255
0x10	1 byte	Function Code 0x10
RRRR	2 byte	Starting Register Addr
NNNN	2 byte	Quantity of Register to write
CCCC	2 byte	CRC CHECKSUM

Example: Write Register 0x0200-0x0201, that is set slave address to 1, and baudrate to 19200bps.
Slave Addr.	1 byte	0x01
Function Code 0x10	1 byte	0x10 (HEX)
Starting Register Addr	2 byte	0x0200 (High8bits first)
Quantity of Register to write	2 byte	0x0002 (High8bits first)
Register Data Byte Count	1 byte	0x04
Register Value: Slave Address	2 byte	0x0001
Register Value: Baudrate	2 byte	0x0004
Checksum	2 byte	0xBACC

Master Request:01 10 0200 0002 04 0001 0004 BACC |||

Slave Addr.	1 byte	0x01
Function Code 0x10	1 byte	0x10 (HEX)
Starting Register Addr	2 byte	0x0200 (High8bits first)
Quantity of Register to write	2 byte	0x0002 (High8bits first)
Register Data Byte Count	1 byte	0x04
Register Value: Slave Address	2 byte	0x0001
Register Value: Baudrate	2 byte	0x0004
Checksum	2 byte	0xBACC

Slave Response:01 10 0200 0002 4070 |||

Slave Response:01 10 0200 0002 4070
Slave Addr.	1 byte	0x01
Function Code 0x10	1 byte	0x10
Starting Register Addr	2 byte	0x0200 (High8bits first)
Quantity of Register to write	2 byte	0x0002 (High8bits first)
Checksum	2 byte	0x4070

Gallery

HEC20 probe inserted in soil among green leaves, its white body and three steel rods in view — Installed in the ground

Dimensioned drawing of the HEC20: body 88 by 26 by 18 millimetres and rods 53 millimetres — Dimensions in millimetres

Documentation

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