SDI-12 Quick Start Guide
Professional FW Version 6.0
HydraProbe SDI-12 Professional FW
SDI-12 communication protocol allows compatible devices to communicate with each other. More information about SDI-12 can be found at http://www.sdi-12.org. 4.1, 4.0, 3.0, 2.8 and 2.7 firmware versions have a different array of commands. Contact Stevens Water for more information.
Model Numbers
| Version Part # Suffix | |
| 2 | Professional, w/25 ft. cable |
| 4 | Professional, w/50 ft. cable |
| 6 | Professional, w/100 ft. cable |
Power
| Power Requirements | 9 to 16 VDC (12VDC Ideal) |
| Power Consumption | <1 mA Idle, 10 mA for 2s Active |
Wiring
| Red Wire | + Power Input |
| Black Wire | Ground |
| Blue Wire | SDI-12 Data Signal |
Addressing
The first character of any command or response on SDI-12 is the sensor address. A lowercase ‘a’ is used to represent the address. Each SDI-12 sensor must have its own unique address. The default address is “0”.
Use SDI-12 “Transparent Mode” to issue commands.
| SDI-12 Command | Response | Description |
| aAb! | b | Change Sensor Address a – Sensor Address b – New Sensor Address |
Identification
A request for identification will return the sensor address, part number, firmware version, sensor version, calibration, and serial number.
| SDI-12 Command | Response | Description |
| aI! | a12STEVENSWnnnnnv.vvvcSNxxxxxxxx | Send Identification a – Sensor address 12 – SDI-12 protocol version STEVENSW – Manufacturer nnnnn – Part number v.vvv – Firmware version c – Calibration xxxxxxxxx – Serial number |
Measurements
| SDI-12 Command | Response | Description |
| am! | attn. | Request Measurement a – Sensor address ttt – seconds (000 – 999) until the measurement is ready n – number of data fields (1-9) in the measurement |
| aD0! | a<F><I><G> | Send Measurement Readings F – Soil Moisture I – Bulk EC (Temp Corrected) G – Temperature (C) |
| aD1! | a<H><J><L> | Send Measurement Readings H – Temperature (F) J – Bulk EC L – Real Dielectric Permittivity |
| aD2! | a<M><K><O> | Send Measurement Readings M – Imaginary Dielectric Permittivity K – Pore Water EC O – Dielectric Loss Tangent |
| aM1! | attn. | Request Measurement tat – seconds (000 – 999) until the measurement is ready n – number of data fields (1-9) in the measurement |
| aD0! | a<L><M><N> | Send Measurement Readings L – Real Dielectric Permittivity M – Imaginary Dielectric Permittivity N – Imaginary Dielectric Permittivity (Temperature Corrected) |
| aD1! | a<O><P> | Send Measurement Readings O – Dielectric Loss Tangent P – Diode Temperature |
The following tables list the values and units:
| Selector Order | Parameter | Unit |
| F | Soil Moisture | Water fraction by Volume (wave) |
| G | Soil Temperature | Celsius (C) |
| H | Soil Temperature | Fahrenheit (F) |
| I | Bulk EC (Temperature Corrected) |
Siemens/Meter (S/m) |
| J | Bulk EC | Siemens/Meter (S/m) |
| K | Pore Water EC | Siemens/Meter (S/m) |
| L | Real Dielectric Permittivity | – |
| M | Imaginary Dielectric Permittivity | – |
| N | Imaginary Dielectric Permittivity (Temperature corrected) |
– |
| O | Dielectric Loss Tangent | – |
| P | Diode Temperature | Celsius (C) |
| SDI-12 Measurement Sets | |||||||||
| Command | P1 | P2 | P3 | P4 | P5 | P6 | P7 | P8 | P9 |
| aM! and aC! | F | I | G | H | J | L | M | K | O |
| aM1! and aC1! | L | M | N | O | P | ||||
Pore Water Offset
| SDI-12 Command | Response | Description |
| aXR_PWOS! | a<Current Offset> | Read Pore Water Offset |
| aXW_PWOS_<New Offset>! | a<New Offset> | Write Pore Water Offset |
| aXD_PWOS! | a+3.4 | Reset Pore Water Offset to default 3.4 |
Calibration
The following extended command will change the coefficients in one of two general formulas that translate the real dielectric permittivity to soil moisture. In many cases, the HydraProbe will not need to be recalibrated. The default General calibration has been heavily reviewed and will provide reasonable accuracy for most applications. If you need to change the calibration or if a custom calibration is required, we recommend referring to the HydraProbe user manual for more information.
| SDI-12 Command | Response | Description |
| aXR_SOIL! | a<G/O/R/C/K> | Get Current soil type G – General O – Organic R – Rockwool C – Custom 1 K – Custom 2 |
| aXR_SOIL_<New Soil Type>! | a<G/O/R/C/K> | Write New Soil Type G – General O –Organic R – Rock Wool C – Custom 1 K – Custom 2 |
| aXR_COEFA! | a<A> | Read coefficient A |
| aXR_COEFA! | a<B> | Read coefficient B |
| aXR_COEFA! | a<C> | Read coefficient C |
| aXR_COEFA! | a<D> | Read coefficient D |
| aXR_COEFA! | a<E> | Read coefficient E |
| aXR_COEFF! | a<F> | Read coefficient F |
| aXR_COEFF! | a<A><B><C><D><E><F> | Read all coefficients |
| aXW_COEFA_<A>! | a<A> | Write coefficient A |
| aXW_COEFA_<B>! | a<B> | Write coefficient B |
| aXW_COEFA_<C>! | a<C> | Write coefficient C |
| aXW_COEFA_<D>! | a<D> | Write coefficient D |
| aXW_COEFA_<E>! | a<E> | Write coefficient E |
| aXR_COEFF_<F>! | a<F> | Write coefficient F |
| aXR_COEFF! | a<A><B><C><D><E><F> | Reset all coefficient to default |
Accuracy and Ranges
| Parameter | |
| Soil moisture for inorganic mineral soils | Accuracy*: +/- 0.01 WFV for most soils ( m3,m-3) +/- <0.03 for fine textured soil (typical) Range: From Complete Dry to Full Saturation (0% to 100% of saturation) |
| Bulk EC | Accuracy: +/- 2.0% or 0.02 S/m Whichever is greater Range: 0 to 1.0 S/m |
| Temperature | Accuracy: +/- 0.3 °C Range: -40 to 75 °C |
| Inter-Sensor Variability | +/- 0.012 WFV (Typical) |
| Pore Water EC | Hillforts Equation, depends on soil conditions |
*Accuracy of soil moisture depends on the soil and is highly variable.
Documents / Resources
 |
STEVENS HydraProbe SDI-12 Professional FW [pdf] User Guide HydraProbe, HydraProbe SDI-12 Professional FW, HydraProbe Professional FW, SDI-12, SDI-12 Professional FW, Professional FW |
