ModularSensors > Modules > Supported Sensors > SDI-12 Sensors > Meter Hydros 21

Meter Hydros 21 module

Classes for the Meter Hydros 21 conductivity, temperature, and depth sensor.

Introduction

A compact 3.4 cm diameter sensor that fits into tight spaces, the HYDROS 21 is a low-cost, durable, and easy-to-use tool for monitoring EC, temperature, and depth in both groundwater and surface water.

The Hydros 21 is implemented as a sub-classes of the SDI12Sensors class. It requires a 3.5-12V power supply, which can be turned off between measurements. While contrary to the manual, they will run with power as low as 3.3V.

Sensor Datasheet

Documentation for the SDI-12 Protocol commands and responses for the Hydros 21 can be found at: http://library.metergroup.com/Manuals/13869_CTD_Web.pdf

Build flags

Sensor Constructor

MeterHydros21(char SDI12address, int8_t powerPin, int8_t dataPin, uint8_t measurementsToAverage = 1)

Construct a new Meter Hydros 21 object.

Parameters
SDI12address The SDI-12 address of the Hydros 21; can be a char, char*, or int.
powerPin

The pin on the mcu controlling power to the Hydros 21. Use -1 if it is continuously powered.

  • The Hydros 21 requires a 3.5-12V power supply, which can be turned off between measurements
dataPin The pin on the mcu connected to the data line of the SDI-12 circuit.
measurementsToAverage The number of measurements to take and average before giving a "final" result from the sensor; optional with a default value of 1.

The SDI-12 address of the sensor, the Arduino pin controlling power on/off, and the Arduino pin sending and receiving data are required for the sensor constructor. Optionally, you can include a number of distinct readings to average. The data pin must be a pin that supports pin-change interrupts.



Example Code

The Meter Hydros21 is used in the menu a la carte example.

#include <sensors/MeterHydros21.h>

const char*   hydros21SDI12address = "1";  // The SDI-12 Address of the Hydros21
const uint8_t hydros21NumberReadings = 6;  // The number of readings to average
const int8_t  hydros21Power = sensorPowerPin;  // Power pin (-1 if unconnected)
const int8_t  hydros21Data  = 7;               // The SDI12 data pin

// Create a Decagon Hydros21 sensor object
MeterHydros21 hydros21(*hydros21SDI12address, hydros21Power, hydros21Data,
                       hydros21NumberReadings);

// Create conductivity, temperature, and depth variable pointers for the
// Hydros21
Variable* hydros21Cond =
    new MeterHydros21_Cond(&hydros21, "12345678-abcd-1234-ef00-1234567890ab");
Variable* hydros21Temp =
    new MeterHydros21_Temp(&hydros21, "12345678-abcd-1234-ef00-1234567890ab");
Variable* hydros21Depth =
    new MeterHydros21_Depth(&hydros21, "12345678-abcd-1234-ef00-1234567890ab");

Classes

class MeterHydros21
The Sensor sub-class for the Meter Hydros 21 conductivity, temperature, and depth sensor.
class MeterHydros21_Cond
The Variable sub-class used for the conductivity output from a Meter Hydros 21 3-in-1 water level sensor..
class MeterHydros21_Temp
The Variable sub-class used for the temperature Output from a Meter Hydros 21 3-in-1 water level sensor..
class MeterHydros21_Depth
The Variable sub-class used for the depth output from a Meter Hydros 21 3-in-1 water level sensor..

Defines

#define HYDROS21_NUM_VARIABLES = 3
Sensor::_numReturnedValues; the Hydros 21 can report 3 values.

Sensor Timing

The sensor timing for a Meter Hydros 21

#define HYDROS21_WARM_UP_TIME_MS = 500
Sensor::_warmUpTime_ms; maximum warm-up time in SDI-12 mode: 500ms.
#define HYDROS21_STABILIZATION_TIME_MS = 0
Sensor::_stabilizationTime_ms; the Hydros 21 is stable as soon as it warms up (0ms stabilization).
#define HYDROS21_MEASUREMENT_TIME_MS = 500
Sensor::_measurementTime_ms; maximum measurement duration: 500ms.
#define HYDROS21_EXTRA_WAKE_TIME_MS = 0
Extra wake time required for an SDI-12 sensor between the "break" and the time the command is sent. The Hydros 21 requires no extra time.

Conductivity

The conductivity variable from a Meter Hydros 21

  • Range is 0 – 120 mS/cm (bulk)
  • Accuracy is ±0.01mS/cm or ±10% (whichever is greater)

MeterHydros21_Cond(MeterHydros21* parentSense, const char* uuid = "", const char* varCode = HYDROS21_COND_DEFAULT_CODE) explicit

Construct a new MeterHydros21_Cond object.

Parameters
parentSense The parent MeterHydros21 providing the result values.
uuid A universally unique identifier (UUID or GUID) for the variable; optional with the default value of an empty string.
varCode A short code to help identify the variable in files; optional with a default value of "Hydros21cond".

#define HYDROS21_COND_RESOLUTION = 1
Decimals places in string representation; conductivity should have 1.

0 are reported, adding extra digit to resolution to allow the proper number of significant figures for averaging - resolution is 0.001 mS/cm = 1 µS/cm

#define HYDROS21_COND_VAR_NUM = 2
Sensor variable number; conductivity is stored in sensorValues[2].
#define HYDROS21_COND_VAR_NAME = "specificConductance"
Variable name in ODM2 controlled vocabulary; "specificConductance".
#define HYDROS21_COND_UNIT_NAME = "microsiemenPerCentimeter"
Variable unit name in ODM2 controlled vocabulary; "microsiemenPerCentimeter" (µS/cm)
#define HYDROS21_COND_DEFAULT_CODE = "Hydros21cond"
Default variable short code; "Hydros21cond".

Temperature

The temperature variable from a Meter Hydros 21

  • Range is -11°C to +49°C
  • Accuracy is ±1°C

MeterHydros21_Temp(MeterHydros21* parentSense, const char* uuid = "", const char* varCode = HYDROS21_TEMP_DEFAULT_CODE) explicit

Construct a new MeterHydros21_Temp object.

Parameters
parentSense The parent MeterHydros21 providing the result values.
uuid A universally unique identifier (UUID or GUID) for the variable; optional with the default value of an empty string.
varCode A short code to help identify the variable in files; optional with a default value of "Hydros21temp".

#define HYDROS21_TEMP_RESOLUTION = 2
Decimals places in string representation; temperature should have 2.

1 is reported, adding extra digit to resolution to allow the proper number of significant figures for averaging - resolution is 0.1°C

#define HYDROS21_TEMP_VAR_NUM = 1
Sensor variable number; temperature is stored in sensorValues[1].
#define HYDROS21_TEMP_VAR_NAME = "temperature"
Variable name in ODM2 controlled vocabulary; "temperature".
#define HYDROS21_TEMP_UNIT_NAME = "degreeCelsius"
Variable unit name in ODM2 controlled vocabulary; "degreeCelsius" (°C)
#define HYDROS21_TEMP_DEFAULT_CODE = "Hydros21temp"
Default variable short code; "Hydros21temp".

Water Depth

The water depth variable from a Meter Hydros 21

  • Range is 0 to 5 m or 0 to 10 m, depending on model
  • Accuracy is ±0.05% of full scale

MeterHydros21_Depth(MeterHydros21* parentSense, const char* uuid = "", const char* varCode = HYDROS21_DEPTH_DEFAULT_CODE) explicit

Construct a new MeterHydros21_Depth object.

Parameters
parentSense The parent MeterHydros21 providing the result values.
uuid A universally unique identifier (UUID or GUID) for the variable; optional with the default value of an empty string.
varCode A short code to help identify the variable in files; optional with a default value of "Hydros21depth".

#define HYDROS21_DEPTH_RESOLUTION = 1
Decimals places in string representation; depth should have 1.

0 are reported, adding extra digit to resolution to allow the proper number of significant figures for averaging - resolution is 2 mm

#define HYDROS21_DEPTH_VAR_NUM = 0
Sensor variable number; depth is stored in sensorValues[0].
#define HYDROS21_DEPTH_VAR_NAME = "waterDepth"
Variable name in ODM2 controlled vocabulary; "waterDepth".
#define HYDROS21_DEPTH_UNIT_NAME = "millimeter"
Variable unit name in ODM2 controlled vocabulary; "millimeter".
#define HYDROS21_DEPTH_DEFAULT_CODE = "Hydros21depth"
Default variable short code; "Hydros21depth".