METER G3 Drain Gauge Instruction Manual

: June 9, 2024
: METER

Table of Contents

METER G3 Drain Gauge
INTRODUCTION
APPLICATIONS
ADVANTAGES
SPECIFICATIONS
G3 DRAIN GAUGE
SENSOR ERROR CODES
SENSOR METADATA VALUE
CUSTOMER SUPPORT
References
Read User Manual Online (PDF format)
Download This Manual (PDF format)

METER G3 Drain Gauge

INTRODUCTION

SENSOR DESCRIPTION
The G3 Drain Gauge is designed for long-term monitoring of soil water drainage to observe soil water movement and chemical leaching accurately and affordably. The G3 Drain Gauge also has a collection system that allows for rapid sampling of drainage waters and for constant water level, temperature, and EC monitoring using a modified HYDROS 21 sensor

APPLICATIONS

Aquifer recharge and recovery
Saltwater intrusion, desalination, and wastewater
Wetland monitoring
Groundwater contamination monitoring
Surface water monitoring

ADVANTAGES

Precision pressure transducer for water depth measurements
Accurate 4-probe EC measurement
Robust thermistor for accurate temperature measurements
Differential pressure measurement referenced to atmospheric pressure so no external pressure sensor is needed
Robust marine-grade epoxy encapsulation to resist corrosive environments
Three-wire sensor interface: power, ground, and data
Digital sensor communicates multiple measurements over a serial interface
Low-input voltage requirements
Low-power design supports battery-operated data loggers
Supports SDI-12 or DDI Serial communications protocols
Modern design optimized for low-cost sensing

PURPOSE OF THIS GUIDE

METER provides the information in this integrator guide to help G3 Drain Gauge customers establish communication between these sensors and their data acquisition equipment or field data loggers. Customers using data loggers that support SDI-12 sensor communications should consult the data logger user manual. METER sensors are fully integrated into the METER system of plug-and- play sensors, cellular-enabled data loggers, and data analysis software.

COMPATIBLE FIRMWARE VERSIONS
This guide is compatible with firmware versions 5.03 or newer for the G3 Drain Gauge.

SPECIFICATIONS

MEASUREMENT SPECIFICATIONS

Drainage

Range 0−61 mm bottom of wick

61−100 mm top of reservoir chambers

Resolution 0.2 mm

Accuracy ±1.4 mm

Water Depth

Range 0−10,000 mm

Resolution 1 mm

Accuracy ±0.25% of full scale at 20 °C

NOTE: Depth measurement accuracy assumes no abrupt temperature variations.

COMMUNICATION SPECIFICATIONS

Output

DDI Serial or

SDI-12 communications protocol

PHYSICAL SPECIFICATIONS

G3 Drain Gauge Dimensions

| Temperature

Range Resolution Accuracy

NOTE: Ice formation with the pressure transducer. temperature could drop be

Bulk Electrical Conduc

Range Resolution Accuracy

NOTE: The EC measureme standard temperature of

Data Logger Compatib

METER ZL6 data log acquisition system power and serial or

Sensor Dimensions

| ****

−40 to +60 °C

0.1 °C

±1 °C

in the G3 Drain Gauge will ruin Remove the sensor if the water

low 0 ºC (32 ºF).

tivity (EC)

0−120,000 µS/cm

1 µS/cm

±10 µS/cm or ±10%, whichever is greater

nt is corrected to a 25 °C.

ility

gers and any data capable of 4.0- to 15-VDC SDI-12 communication

---|---|---
Mass| 20.0 kg (44.0 lb) with stainless steel DCT

14.0 kg (31.0 lb) with PVC DCT

Access Tube Dimensions

20 m

40 m (maximum)

|
Outer Diameter| 11.5 cm (4.5 in)
Material| Schedule 40 PVC| |
Cable Diameter| | Connector Diameter
---|---|---
4.20 mm (0.165 in) with a

minimum jacket of 0.76 mm (0.030 in)

EQUIVALENT CIRCUIT AND CONNECTION TYPES

Refer to Figure 2 and Figure 3 to connect the G3 Drain Gauge to a data logger. Figure 2 provides a low-impedance variant of the recommended SDI-12 specification.

G3 DRAIN GAUGE

SURGE CONDITIONS
Sensors have built-in circuitry that protects them against common surge conditions. Installations in lightning-prone areas, however, require special precautions, especially when sensors are connected to a well-grounded third- party logger. Read the application note Lightning surge and grounding practices on the METER website for more information.

POWER AND GROUNDING
Ensure there is sufficient power to simultaneously support the maximum sensor current drain for all the sensors on the bus. The sensor protection circuitry may be insufficient if the data logger is improperly powered or grounded. Refer to the data logger installation instructions. Improper grounding may affect the sensor output as well as sensor performance. Read the application note Lightning surge and grounding practices on the METER website for more information.

CABLES
Improperly protected cables can lead to severed cables or disconnected sensors. Cabling issues can be caused by many factors, including rodent damage, driving over sensor cables, tripping over the cable, not leaving enough cable slack during installation, or poor sensor wiring connections. To relieve strain on the connections and prevent loose cabling from being inadvertently snagged, gather and secure the cable travelling between the G3 Drain Gauge and the data acquisition device to the mounting mast in one or more places. Install cables in conduit or plastic cladding when near the ground to avoid rodent damage. Tie excess cable to the data logger mast to ensure cable weight does not cause sensor to unplug. The G3 Drain Gauge cable has an integrated vent tube to provide an atmospheric pressure reference for the depth sensor. The cable should be installed without sharp bends that would crimp this internal vent tube. Please see the G3 Drain Gauge User Manual (publications.metergroup.com/Manuals/20677_G3 Drain GaugeManual Web.pdf) for more information on sensor installation and protecting this vent.

SENSOR COMMUNICATIONS METER
digital sensors feature a serial interface with shared receive and transmit signals for communicating sensor measurements on the data wire (Figure 3). The sensor supports two different protocols: SDI-12 and DDI Serial. Each protocol has implementation advantages and challenges. Please contact Customer Support if the protocol choice for the desired application is not obvious.

SDI-12 INTRODUCTION
SDI-12 is a standards-based protocol for interfacing sensors to data loggers and data acquisition equipment. Multiple sensors with unique addresses can share a common 3-wire bus (power, ground, and data). Two-way communication between the sensor and logger is possible by sharing the data line for transmit and receive

Table 1 SDI-12 communication configuration

DDI SERIAL INTRODUCTION
The DDI Serial protocol is the method used by the METER data loggers for collecting data from the sensor. This protocol uses the data line configured to transmit data from the sensor to the receiver only (simplex). Typically, the receive side is a microprocessor UART or a general-purpose I/O pin using a bitbang method to receive data. Sensor measurements are triggered by applying power to the sensor.

INTERFACING THE SENSOR TO A COMPUTER
The serial signals and protocols supported by the sensor require some type of interface hardware to be compatible with the serial port found on most computers (or USB-to-serial adapters). There are several SDI-12 interface adapters available in the marketplace; however, METER has not tested any of these interfaces and cannot make a recommendation as to which adapters work with METER sensors. METER data loggers and and the ZSC and PROCHECK handheld devices can operate as a computer-to-sensor interface for making on-demand sensor measurements. For more information, please contact Customer Support.

METER SDI-12 IMPLEMENTATION
METER sensors use a low-impedance variant of the SDI-12 standard sensor circuit (Figure 2). During the power-up time, sensors output some sensor diagnostic information and should not be communicated with until the power-up time has passed. After the power-up time, the sensors are fully compatible with all commands listed in the SDI-12 Specification v1.3 except for the continuous measurement commands ( aR3 and aRC3 ). See page 7 for M , R , and C command implementations. Out of the factory, all METER sensors start with SDI-12 address 0 and print out the DDI Serial startup string during the power- up time. This can be interpreted by non-METER SDI-12 sensors as a pseudo-break condition followed by a random series of bits. The G3 Drain Gauge will omit the DDI Serial startup string when the SDI-12 address is nonzero or if

is set to 1. Changing the address to a nonzero address is recommended for this reason.

	Table 2 aM! command sequence
Command	Response
aM!	atttn
aD0!	a+±+

NOTE: The measurement and corresponding data commands are intended to be used back to back. After a measurement command is processed by the sensor, a service request a is sent from the sensor signaling the measurement is ready. Either wait until ttt seconds have passed or wait until the service request is received before sending the data commands. See the SDI-12 Specifications v1.3

SENSOR BUS CONSIDERATIONS
SDI-12 sensor buses require regular checking, sensor upkeep, and sensor troubleshooting. If one sensor goes down, that may take down the whole bus even if the remaining sensors are functioning normally. Power cycling the SDI-12 bus when a sensor is failing is acceptable, but METER does not recommend scheduling power cycling events on an SDI-12 bus more than once or twice per day. Many factors influence the effectiveness of the bus configuration. Visit metergroup.com for articles and virtual seminars containing more information.

	Table 3 aC! measurement command sequence
Command	Response
aC!	atttnn
aD0!	a±±+

NOTE: Please see the SDI-12 Specifications v1.3 document for more information.

SENSOR ERROR CODES

The G3 Drain Gauge has four error codes:

9999 is output in place of the measured value if the sensor detects that the measurement function has been compromised and the subsequent measurement values have no meaning.
9992 is output in place of the measured value if the sensor detects corrupt or lost calibrations.
991 is output in place of the measured value if the sensor detects insufficient voltage to perform the measurement.
9990 is output in place of the measured valve if the sensor measurement is out of range.

SDI-12 TIMING
All SDI-12 commands and responses must adhere to the format in Figure 4 on the data line. Both the command and response are preceded by an address and terminated by a carriage return and line feed combination ( ) and follow the timing shown in Figure 5.

	Table 4 aV! measurement command sequence
Command	Response
aV!	atttnn
aD0!	a±

COMMON SDI-12 COMMANDS
This section includes tables of common SDI-12 commands that are often used in an SDI-12 system and the corresponding responses from METER sensors.

Table 5 G3 Drain Gauge aXO! measurement command sequence

Command| Response
aXO!| a+
aXO !| aOK
NOTE: Command uses capital O| as in Oscar (not zero).

IDENTIFICATION COMMAND ( aI! )
The Identification command can be used to obtain a variety of detailed information about the connected sensor. An example of the command and response is shown in Example 1, where the command is in bold and the response follows the command.

	Table 6 G3 Drain Gauge aXR3! measurement command sequence
Command	Response
aXR3!	a

CHANGE ADDRESS COMMAND ( aAB! )
The Change Address command is used to change the sensor address to a new address. All other commands support the wildcard character as the target sensor address except for this command. All METER sensors have a default address of 0 (zero) out of the factory. Supported addresses are alphanumeric (i.e., a – z , A – Z , and 0 – 9 ). An example output from a METER sensor is shown in Example 2, where the command is in bold and the response follows the command. METER G3 Drain Gauge 5

	Table 7 G3 Drain Gauge aR0! measurement command sequence
Command	Response
aR0!	a±±+

NOTE: This command does not adhere to the SDI-12 response timing. See METER SDI-12 Implementation for more information.

ADDRESS QUERY COMMAND
(?!) While disconnected from a bus, the Address Query command can be used to determine which sensors are currently being communicated with. Sending this command over a bus will cause a bus contention where all the sensors will respond simultaneously and corrupt the data line. This command is helpful when trying to isolate a failed sensor. Example 3 shows an example of the command and response, where the command is in bold and the response follows the command. The question mark ( ? ) is a wildcard character that can be used in place of the address with any command except the Change Address command METER
G3 Drain Gauge 6

	Table 8 G3 Drain Gauge aR3! measurement command sequence
Command	Response
aR3!	a

NOTE: This command does not adhere to the SDI-12 response format or timing. See METER SDI-12 Implementation for more information. The values in this command are space delimited. As such, a + sign is not assigned between values and a – sign is only present if the value

COMMAND IMPLEMENTATION The following tables list the relevant Measurement ( M ), Continuous ( R ), and Concurrent ( C ) commands and subsequent Data ( D ) commands, when necessary. METER G3 Drain Gauge 7

PARAMETERS
Table 9 lists the parameters, unit measurement, and a description of the parameters returned in command responses for G3 Drain Gauge.

		Table 9 Parameter Descriptions
Parameter	Unit	Description
±	—	Positive or negative sign denoting sign of the next value
a	—	SDI-12 address
n	—	Number of measurements (fixed width of 1)
nn	—	Number of measurements with leading zero if necessary (fixed width of

ttt| s| Maximum time measurement will take (fixed width of 3) | —| Tab character **Table** **9** **Parameter Descriptions (continued)** --- **Parameter**| **Unit**| **Description** | —| Carriage return character | —| Line feed character | µS/cm| Electrical conductivity | mm| Depth—Values will typically range from 0 to 4,000 mm | °C| Temperature | —| ASCII character denoting the sensor type For G3 Drain Gauge, the character is e | —| Auxilliary sensor information See Table 10 | —| 0: DDI Serialunsuppressed

1: DDI Serialsuppressed

| —| METER 6-bit CRC | —| METER serial checksum

SENSOR METADATA VALUE

The sensor metadata value contains information to help alert users to sensor- identified conditions that may compromise optimal sensor operation. The output of the aV! aD0! sequence will output a integer value. This integer represents a binary bitfield, with each individual bit representing an error flag. Table 10 lists the possible error flags that can be set by the G3 Drain Gauge. If multiple error flags are set, the sensor metadata integer value will be the sum of the individual values. To decode an integer value not explicitly in Table 10, find the largest error flag value that will fit in the integer value and accept that error as being present. Then, subtract that error flag value from the integer value and repeat the process on the remainder until the result is zero. For example, a sensor metadata integer value of 129 is the sum of the individual error flag values 128 + 1 , so this sensor has corrupt firmware and experienced temperatures below freezing.. METER G3 Drain Gauge
8

Table 10 Error Flag Values and Issue Resolution

DDI SERIAL COMMUNICATION
The DDI Serial communications protocol is ideal for systems that have dedicated serial signaling lines for each sensor or use a multiplexer to handle multiple sensors. The serial communications are compatible with many TTL serial implementations that support active-high logic levels using 0.0–3.6 V signal levels. When the sensor is first powered, it automatically makes measurements of the integrated transducers then outputs a response over the data line. Systems using this protocol control the sensor excitation to initiate data transfers from the sensor. This protocol is subject to change as METER improves and expands the line of digital sensors and data loggers. The HYDROS 21 will omit the DDI Serial message when the SDI-12 address is nonzero or suppressed with the aXO1! command. METER recommends suppressing the DDI Serial message when this signaling causes negative issues for a sensor measurement device. NOTE: Out of the factory, all METER sensors start with SDI-12 address 0 and print out the startup string when power cycled. METER G3
Drain Gauge 10

DDI SERIAL TIMING
Table 11 lists the DDI Serial communication configuration.

Table 11 DDI Serial communication configuration

At power up, the sensor will pull the data line high within 100 ms to indicate that the sensor is taking a reading (Figure 6). When the reading is complete, the sensor begins sending the serial signal out the data line adhering to the format shown in Figure 7. Once the data is transmitted, the sensor goes into SDI-12 communication mode. To get another serial signal, the sensor must be power cycled.

DDI SERIAL RESPONSE
Table 12 details the DDI Serial response.

Table 12 G3 Drain Gauge DDI Serial response

COMMAND| RESPONSE
NA|

**NOTE: There is no actual command. The response is returned automatically upon power up. The values in this command are space delimited.** **As such, a + sign is not assigned between values and a – sign is only present if the value is negative.**

DDI SERIAL CHECKSUM
These checksums are used in the continuous commands R3 , and XR3 , as well as the DDI Serial response. The legacy checksum is deprecated in favor of the CRC6 check character and may be ignored. The legacy checksum is computed using the characters after the sensor address (when used with the R3 or XR3 command) and includes the sensor identification character.

G3 Drain Gauge example input is 146 21.9 1034 0eYg and the resulting checksum output is Y .

G3 Drain Gauge CRC6 checksum example input is 146 21.9 1034 0eYg and the resulting checksum output is g .

CUSTOMER SUPPORT

NORTH AMERICA
Customer service representatives are available for questions, problems, or feedback Monday through Friday, 7:00 am to 5:00 pm Pacific time.

Email: support.environment@metergroup.com
sales.europe@metergroup.com
Phone: +1.509.332.5600
Fax: +1.509.332.5158
Website: metergroup.com

EUROPE
Customer service representatives are available for questions, problems, or feedback Monday through Friday, 8:00 to 17:00 Central European time.