Xylem H-312-22 User Manual

Model

H-312 and H-312-22

Submersible Pressure Sensor

With SDI-12 Output

Owner's Manual

Version 1.1

75 West 100 South, Logan, Utah 84321 Phone: [phone] Fax: [phone] Web: http://www.waterlog.com E-mail: [e-mail]

D E S I G N A N A L Y S I S A S S O C I A T E S , I N C .

75 West 100 South, Logan, Utah 84321 Phone: [phone] Fax: [phone] Web: http://www.waterlog.com E-mail: [e-mail]

D E S I G N A N A L Y S I S A S S O C I A T E S , I N C .

User Agreement/

W

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1. NATURE OF THE PRODUCT

This agreement accompanies a pressure measuring system comprising firmware, circuitry and other
electronic equipment in an enclosed housing, and packaged together with written instructional materials.
The packaged electronic circuitry and instructional materials herein are collectively referred to as the
“PRODUCT.” The PRODUCT is made available from DESIGN ANALYSIS ASSOCIATES, INC., of
75 West 100 South, Logan, Utah 84321 (hereinafter referred to as “DESIGN ANALYSIS”), and contains
information and embodies technology that is confidential and proprietary to DESIGN ANALYSIS, and the
availability and use of the PRODUCT is extended to you, the USER, solely on the basis of the terms of
agreement which follow.

2. ACKNOWLEDGMENTS BY USER

Opening the package which encloses the accompanying PRODUCT indicates your acceptance of the terms
and conditions of this agreement and constitutes an acknowledgment by you of the confidential and
proprietary nature of the rights of DESIGN ANALYSIS in the PRODUCT.

3. DUTIES OF YOU, THE USER

In consideration for the access to and use of the PRODUCT extended to you by DESIGN ANALYSIS and
to protect the confidential and proprietary information of DESIGN ANALYSIS, USER agrees as follows:

(a) USER agrees that they will not remove from the exterior of the housing of the PRODUCT

any safety warnings or notices of proprietary interest placed thereon by DESIGN
ANALYSIS.

LOG® Warranty

(b) USER agrees that they shall not disassemble or otherwise reverse engineer the

PRODUCT.

(c) USER agrees to treat the PRODUCT with the same degree of care as USER exercises in

relation to their own confidential and proprietary information.

4. TERM

USER may enjoy these rights only as long as their possession of the PRODUCT shall continue to be
rightful. These rights will cease if the PRODUCT is returned to DESIGN ANALYSIS under the terms of
any redemption offer, warranty, or money-back guarantee, or if USER transfers the PRODUCT to another
party on terms inconsistent with this agreement.

5. LIMITED WARRANTY
(a) What is Covered

DESIGN ANALYSIS warrants that for a period of twelve months from the time of delivery the
functions to be performed by the PRODUCT will be substantially in compliance with USER
documentation. DESIGN ANALYSIS also warrants that the PRODUCT will be free from defects
in materials and workmanship for a period of ONE YEAR from the date of delivery.

(b) What USER Must Do

If the product fails to satisfy the above warranty, USER must notify DESIGN ANALYSIS in

H-312

User Agreement/W

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LOG® Warranty W-1

writing within the applicable period specified above and reasonably cooperate with the directions
they received from DESIGN ANALYSIS.

(c) What DESIGN ANALYSIS Will Do

DESIGN ANALYSIS will repair the PRODUCT or will endeavor to provide a replacement of
same within a reasonable period of time. In the event that DESIGN ANALYSIS is unable to make
the necessary repairs or replacement within a reasonable period of time, the original purchase price
will be refunded upon the return of the PRODUCT to DESIGN ANALYSIS.

(d) Limitations

(i) THE ENTIRE REMEDY FOR BREACH OF THIS LIMITED WARRANTY

SHALL BE LIMITED TO REPLACEMENT OF THE DEFECTIVE
PRODUCT OR REFUNDING OF THE PURCHASE PRICE, AS SET FORTH
ABOVE. IN NO EVENT WILL THE LIABILITY OF DESIGN ANALYSIS
TO USER OR TO ANY OTHER PARTY EXCEED THE ORIGINAL
PURCHASE PRICE OF THE PRODUCT, REGARDLESS OF THE FORM OF
THE CLAIM.

(ii) EXCEPT FOR THE EXPRESS WARRANTIES ABOVE, DESIGN ANALYSIS

SPECIFICALLY DISCLAIMS ALL OTHER WARRANTIES, INCLUDING,
WITHOUT LIMITATION, ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

(iii) UNDER NO CIRCUMSTANCES WILL DESIGN ANALYSIS BE LIABLE

FOR SPECIAL, INCIDENTAL, CONSEQUENTIAL, INDIRECT, OR ANY
OTHER DAMAGES OR CLAIMS ARISING FROM THE USE OF THIS
PRODUCT, THIS INCLUDES LOSS OF PROFITS OR ANY OTHER
COMMERCIAL DAMAGES, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES. IN NO EVENT WILL DESIGN ANALYSIS BE LIABLE
FOR ANY CLAIMS, LIABILITY, OR DAMAGES ARISING FROM
MODIFICATION MADE THEREIN, OTHER THAN BY DESIGN
ANALYSIS.

(iv) THIS LIMITED WARRANTY GIVES USER SPECIFIC LEGAL RIGHTS.

USER MAY ALSO HAVE OTHER RIGHTS WHICH VARY FROM STATE
TO STATE. SOME STATES DO NOT ALLOW LIMITATIONS ON HOW
LONG AN IMPLIED WARRANTY LASTS OR THE EXCLUSION OF
INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THOSE
LIMITATIONS OR EXCLUSIONS MAY NOT APPLY.

6. GOVERNING LAW

This Agreement and its validity and interpretation shall be governed by the laws of the State of Utah,
notwithstanding any choice of law rules of Utah or any other state or jurisdiction.

W-2 User Agreement/W

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LOG® Warranty

H-312

1.0 Introduction

Chapter 1

Introduction

The W
level monitoring. The H-312 is easy to use and works with any SDI-12 data recorder. The
“Serial-Digital Interface” is ideal for data logging applications with the following requirements.

 Battery powered operation with minimal current drain
 Pressure measurement data is transmitted digitally over long cable lengths without error
 Multiple sensors on a simple three-wire cable
 Up to 250 feet of cable between a sensor and the data recorder

The H-312 has the following features:

 Simple to install, use, and maintain (no on-site calibration required)
 Performs extremely accurate measurements.
 Linear deviation is less than 0.05%
 Resolution is 1 part in 1,000,000
 Accuracy over temperature range exceeds ±0.02 ft. of water
 Enclosure is nonconductive and corrosion proof
 Stainless steel sensor diaphragm
 Sensor cable has internal atmospheric vent for compensation of barometric pressure changes
 Junction box provides access for inspection and maintenance of dry-air desiccant
 Low current operation (less than 150 microamps typical standby)
 Suspension bail provides positive control of the sensor depth independent of temperature and

 Extended SDI-12 commands for setting the Stage to the current water elevation.

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LOG® H-312 is a submersible pressure transducer specifically designed for water

(Use of H-423, SDI-12 to RS485 converter extends the range to 1000's of feet)

age dependent changes to the sensor cable.

H-312

Introduction 1-1

1.1 Unpacking

The following is a list of items you should have received:

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 W

junction box

 Stainless steel ballast
 Spare desiccant packs
 Owner's Manual
 Stainless steel suspension cable and miscellaneous hardware (optional)

LOG® H-312 pressure transducer with polyurethane vented cable and dry air

1-2 Introduction

Figure 3 H-312 Pressure Sensor Components

H-312

1.2 Check The Sensor Cable

Be sure that the vented cable is long enough to reach from the submerged location selected to the
junction box of the dry air system. Also, be sure that the data logger cable is long enough to
reach from the dry air junction box to your data recorder

1.3 Check The Model Number

Before installing your new W
enclosure. Check the model number, the range, and the output type to be sure that you have
received the instrument you ordered. The label will look similar to the following:

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LOG® H-312, check the information on the label of the sensor

H-312

Model

Submersible Pressure Sensor

S/N 1103
Range: 0-15 PSI (34.6' H20)
Output:: SDI-12
Input: 10 to 16.0 Volts

that the W
model works with a recording device that follows the SDI-12 protocol.

ATER

LOG® H-312-15 measures pressure within the range from zero to 15 psi. This

.

This example shows

H-312

Introduction 1-3

1-4 Introduction

H-312

Chapter 2

Installation

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2.1 Installing the W

The H-312 submersible pressure sensor is very versatile and can be used in many water
monitoring applications.

LOG® H-312

Figure 4 H-312 System Components

Before proceeding with the installation, please consider several site preparation and maintenance
issues:

H-312

Installation 2-1

2.2 Water Depth

The following chart shows the maximum depth to which the H-312 is factory calibrated. The
sensor can survive temporary operation up to twice the maximum rated depth for you model’s
range. However, any pressure measurements made beyond the rated depth will be inaccurate.
The H-312 will be damaged if it is placed deeper than twice the maximum rated depth.

Model Pressure Range Depth Range

*

Accuracy
H-312-15 0 to 15 psi 0 to 34.60 ft. +0.017 ft
H-312-30 0 to 30 psi 0 to 69.20 ft. +0.035 ft.

* NOTE: Depth calculations are derived from the standard equation that one PSI is generated by
a column of water 27.680 inches deep at 39.4F.

2.3 General Installation Recommendations

The sensor must be located where there is no velocity flow. Changes in water flow cause pressure
changes. Thus, if the sensor is subjected to open flow there is a good chance your water level
measurements will be inconsistent. To obtain accurate and reliable data, use stilling wells, sand
points, or other "no flow" installation techniques.

The H-312 submersible pressure transducer is not recommended for use in applications where silt
and mud are problematic. In addition, if the sensor is used in a shallow water application and
happens to dry out with mud coating the sensor diaphragm, the diaphragm compliance will be
altered and the factory calibration spoiled.

The H-312 sensor will be permanently damaged if it is frozen. Transducers which are installed in
geographical areas with harsh winters should be removed for the winter unless they are installed
deep enough in the water that there is no danger of freezing. Ice may form around the sensor
cable without causing damage or performance degradation. However, the cable should be
protected so as to minimize the possibility of it being damaged as the ice shifts or breaks up
during times of thawing.

The polyurethane drop cable is suitable for immersion, direct burial and is somewhat ultraviolet
(UV) resistant. Whenever possible, precautions should be taken to protect the cable from direct
sunlight, rodents and mechanical damage.

Experience has shown that if a portion of the H-312 housing or the sensor cable is installed above
the water and exposed to sunlight (e.g. installed in shallow water), a temperature gradient can
occur inside the enclosure and vent tube. As the air temperature changes the air density changes.
A change in the air density inside the sensor or vent tube column causes a partial pressure on the
reference side of the sensor which will raise or lower the H-312's pressure reading. This is a "law
of physics" problem not unique to W

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LOG® Series transducers. It can be avoided by

installing the transducer horizontal so that the entire enclosure is covered by water. Cover or

2-2 Installation

H-312

protect the sensor cable so it remains at the temperature of the surrounding air and is not heated
directly by the sun.

2.4 Stilling Wells

The H-312 can be hung in well bores, stilling wells and stand­pipes. The H-312 should be installed by suspending the sensor
using a small stainless steel cable, not by its polyurethane
electrical cable. A weighted ballast or sinker, such as the one
that is provided will pull the cable tight at the desired depth and
will help the sensor to hang straight down. The stainless cable
and the miscellaneous hardware can be purchased from Design
Analysis Associates, or from a number of other sources.

The polyurethane cable has internal kevlar strength members
however, the plastic cable construction has a large thermal
coefficient of expansion. This coupled with the fact that the
cable will stretch with applied weight, make the use of the
stainless steel drop cable necessary for all precision
measurements.

Attach one end of the stainless steel support cable to the
support bail on the sensor and fasten the other end to a fixed
reference point at the surface. Attach the ballast to the sensor
using the stainless steel ring on the bottom nose of the sensor.

When installing the H-312 in wells or stand pipes, make certain
the surface of the water in the pipe is open to the atmosphere.
Well pipes are often capped with a sanitary well seal or locking
cap, make certain the well cap has a suitable hole or screened
vent.

H-312

Installation 2-3

2.5 Dry Air Junction Box

Because the surface of the water being measured is exposed to atmospheric pressure, submersible
pressure sensors must provide correction for changes in barometric air pressure. Several industry
designs employ a sealed sensor housing and measure the atmospheric pressure separately. This
scheme however, doubles the offset drift because two pressure sensors are needed. To provide
the best accuracy possible, the H-312 uses an atmospheric referenced pressure sensor design. The
submerged pressure sensor in the H-312 has a vent tube connected to the back side it’s pressure
diaphragm.. The vent tube passes up the drop cable and is open to the atmosphere at the top.
Vent tube designs however, are susceptible to moisture condensation in the tube. As the
atmospheric pressure changes small amounts of air flow up and down the vent tube. Convection
can also contribute to airflow within the vent tube. If the vent tube is colder than the dew point of
the air, moisture will condense in the tube. This condition occurs continually because the
submerged portion of the vent tube is maintained at the water temperature. The temperature of
both surface and ground water are normally well below the dew point of the surrounding air.

The H-312 dry air junction box
provides for terminating the
polyurethane sensor cable and
houses desiccant for keeping the
atmospheric vent tube dry. The
enclosure has a transparent lid
which allows visual inspection of
the desiccant packs. The
enclosure has a small screened
vent port in the top cover which
exposes the sensor vent tube to
the atmosphere.

Figure 6 Dry Air Junction Box

The dry air junction box should
be installed in a protected, dry,
location such as an instrument shelter. The installation should provide easy access and facilitate
regular inspection and maintenance of the desiccant.

2.6 Making Connections to the H-312

The H-312 is a SDI-12 V1.2 compliant sensor. It connects directly to any data recorder with
SDI-12 capability. The dry air junction box has a 4-conductor pigtail cable for making
connections to your data logger. The pigtail cable can be modified or replaced in the field. The
table below shows the proper connections to the pigtail. The power for the H-312 is supplied by
the SDI-12 +12V input. The connections are also shown on a wiring diagram inside the dry air
junction box.

2-4 Installation

H-312

Figure 7 Dry Air Junction Box Wiring

Data Logger Connections

Wire Name

Red
White
Black
Shield

If the polyurethane cable between the H-312 sensor and the dry air junction box must be routed
thru a conduit or small hole, the polyurethane cable can be temporarily disconnected from the dry
air junction box as needed. Reconnect the sensor cable as shown below:

H-312 Sensor Connections

Wire Name

Red
White

Black + Green

Shield

+12Volt DC

SDI-12 Data

Ground
Ground

+12Volt DC

SDI-12 Data

GND

Shield

H-312

Installation 2-5

2.7 Wiring and Installation Precautions

 The shield in the hook-up cable must be connected to the data logger ground.
 The data recorder must be earth grounded.
 The H-312 requires that the water be at ground potential. Mother Nature takes care of this

for surface and ground water.

 Make certain the seals in the liquid tight cable fittings on the dry air junction box are tight.
 Make certain the dry air junction box lid is screwed on and sealed properly.
 Make certain the screened vent port on the lid of the dry air junction box is not covered or

blocked.

 Make certain the end of the vent tube inside the dry air junction box is not plugged or

blocked.

 Check the desiccant packs. Replace if necessary

2.8 Programming Your Data Recorder

You must prepare your data recorder to receive and record the H-312 data. Since data recorders
differ widely, refer to your recorder manufacturer's directions. In general, program the data
recorder to input four values via the SDI-12 port. Usually only one or two of the parameters is
actually recorded. Your data recorder must issue an “aM!” command, then collect the data with a
“aD0" command, as explained in Chapter 4. The H-312 places four parameters in its data buffer:

Where:

a+AA.AAA+BB.BBB+CC.C+DD.D<cr><lf>

a = SDI-12 address 0-9, A-Z
AA.AAA = Stage (feet, inches, meters etc.)
BB.BBB = Pressure (PSI)
CC.C = Temperature (C)
DD.D = Sensor Supply Voltage (Volts)

2-6 Installation

H-312

2.9 Programming the SDI-12 Address

If more than one sensor is to be connected to the SDI-12 bus, make certain each sensor has a
different sensor address. The H-312 comes from the factory with its address set to “0". The
address can be changed with an extended SDI-12 command (see Chapter 4).

2.10 Programming the H-312 Sensor

The H-312 comes from the factory with the following settings:

SDI Address: 0

Slope: 2.3067 (feet of H
Offset : 0.00
MeanCount: 16

With these values the Stage will be in units of feet when used in clean water. The slope can be
changed to accommodate other engineering units such as inches or Meters. The setups are stored
in EEPROM within the H-312 and will not be lost if the power is disconnected. The extended
commands for changing these setups are described in detail in Chapter 4.

MeanCount is the number of raw pressure measurements averaged together to make one SDI-12
measurement sequence. This setting determines how long the sensor will take to make a
measurement. MeanCount can be changed as described in Chapter 4.

0)

2

2.11 Setting the Stage

Many applications use the pressure sensor in a stilling well. The submerged sensor translates
pressure to water level. When the H-312 is first installed, you will want to adjust the Offset such
that the SDI-12 measurement data (Stage) corresponds to the current water elevation or stage as
determined with a staff gauge or other datum.

An extended SDI-12 command is convenient to quickly set the H-312's Stage reading to match
the current water level. The “aXSCSdd.d!” command causes the H-312 to make a fresh
measurement and automatically update the Offset as needed to produce the desired Stage. See
Chapter 4 for details.

Example of a H-312 Extended "Set Current Stage" command:

Command
"aXSCS2.3!" "a0031<cr><lf>" 3sec 1 Set the Stage to 2.3

Subsequent Command
"aD0" a+12.80<cr><lf> The new Offset

Response Time Values Description

Response Description

H-312

Installation 2-7

2.12 Testing

Before installing the H-312 in your field location, you may wish to first test the sensor and data
logger in your shop or lab. This allows you to become familiar with H-312 and the data logger in
a controlled environment. The H-312 can be tested in a bucket of water. However, for this test to
work correctly, you must run a wire from inside the bucket that comes in contact with the water
back to the chassis ground of the data recorder. The wire establishes a ground connection
between the water and the data logger. Water and other conductive objects isolated by a plastic
bucket or table surface pick up AC noise from nearby lighting and power lines. The AC noise is
coupled by the water to the stainless diaphragm in the submerged pressure sensor. Because the
H-312 has a non-conductive housing it is electrically isolated from the surrounding water. The AC
noise may affect the pressure measurement due to large voltages between the water media and the
sensor (data logger) ground. This precaution is not necessary for field installations because
surface water and ground water are not isolated from earth ground.

2-8 Installation

H-312

Chapter 3

Maintenance

3.1 Maintenance

Sustained operation of the H-312 pressure sensor is almost maintenance-free. Experience has
shown that moisture condensing in the atmospheric reference tube creates the largest percentage
of field problems. The desiccant in the H-312 junction box dry air system should be changed on a
fixed schedule, normally every three to six months. Different areas in the world have widely
varying humidity and temperature fluctuations. Pay close attention to the desiccant condition in
your particular installation. The desiccant packs contain indicating silica gel and have a
transparent window that allows the condition of the desiccant to be observed. The silica gel has a
blue color when dry and changes to pink as it absorbs moisture.

3.2 Changing the Desiccant

The desiccant in the H-312 junction box dry air system is easy to change.

Step 1 Remove the clear plastic lid.

Step 2 Replace the desiccant packs

Step 4 Reinstall the clear plastic lid.

Precautions

 Make certain the seals in the

liquid tight cable fittings on the
dry air junction box are tight.

 Make certain the dry air junction box lid is screwed on and sealed properly.
 Make certain the screened vent port on the lid of the dry air junction box is not covered or

blocked.

3.3 Maintaining Desiccant Packs

The desiccant bags have a transparent strip which allows the condition of the desiccant to be
visually checked. The desiccant has a dark blue color when dry and changes to pink as it absorbs
moisture. The desiccant packs can be reused by drying them in an oven at 180F to 220F for 4
to 8 hours or until the desiccant returns to a dark blue color.

Figure 8 Dry Air Junction Box

H-312

Maintenance 3-1

3.4 Cleaning the Port Screen

The H-312 has a port screen to help prevent dirt, sediment and insects from entering the sensor
pressure port. The screen is a circular stainless steel band with .025 square holes. A 149 micron
polypropylene plastic screen is located underneath the stainless screen.

Occasionally the port screen and the pressure ports may need to be cleaned, rinsed out or replaced
. Replacement stainless steel and polypropylene screens are available if needed. The photo below
shows the dissembled components at the bottom end of the sensor housing. Do not remove the
rubber grommet on the cable end of the sensor housing, the snap-ring or any of the internal
components. If the sensor is disassembled the pressure sensor generally must be re-calibrated at
the factory. To service the port screen perform the following steps.

Figure 9 Cleaning the Port Screen

Step 1 Unscrew the lower end-piece from the sensor housing (the tapered end cap).

Step 2 Remove the stainless and polypropylene screens.

Step 3 Clean or replace the screens as needed.

Step 4 The internal nose of the H-312 has two threaded pressure ports located 180 apart. These

ports are used in the factory to make connections in the calibration oven. Rinse the
pressure ports with water to clear mud and silt. You may want to swish the sensor in a
bucket of water or in the stream it is monitoring to rinse out the pressure ports.

3-2 Maintenance

H-312

CAUTION: Do not use sticks and the like to push sediment out of the ports. This may

cause a hydraulic effect and over pressure the internal sensor. Use common
sense.

Step 5 Reinstall the plastic and the stainless steel screens. Position the joints of the stainless and

plastic screens 180 apart. One end of the stainless steel screen has a slight bend. Position
the bent end on the outside to help keep the sharp end from protruding out. Compress the
screen with a turning action and slip both screens into the shallow groove in the sensor
housing..

Step 6 Screw the nose piece into place until it contacts the screens. Twist the screens until both

screens slip into the grooves of both the sensor housing and the nose piece. Continue to
tighten the nose piece while being careful to not crinkle the screens. You may need to
twist the screens now and then to keep the screens centered in the grooves. Fully hand
tighten the nose piece.

3.5 Trouble Shooting

Experience over the years with submersible sensors has identified several common problems:

No SDI-12 response or intermittent data

1. Check all wiring including power and ground connections. Battery connections can
become corroded.

2. The H-312 measures and reports it’s internal power supply voltage along with
Stage and Pressure. Make a measurement and check to see if the voltage is
between 10.0 and 16.0 Volts.

3. Check the connections between your data recorder and the H-312 sensor.

Wire Name

Red
White
Black
Shield

Offset Drift

Check the desiccant packs. If moisture accumulates in or blocks the vent tube, barometric
pressure changes will affect the pressure measurement. If this is the case, you should contact
Design Analysis for instructions as how to proceed.

+12Volt DC

SDI-12 Data

Ground
Ground

H-312

Maintenance 3-3

3-4 Maintenance

H-312

Chapter 4

SDI-12 Command and Response Protocol

4.0 SDI-12 Command and Response Protocol

This is a brief description of the Serial Digital Interface (SDI-12) Command and Response
Protocol used by the W
commands and data format supported by the H-312.

Refer to the document "A SERIAL DIGITAL INTERFACE STANDARD FOR HYDROLOGIC
AND ENVIRONMENTAL SENSORS.” Version 1.2 April 12, 1996 Coordinated by the SDI-12
Support Group, 135 East Center, Logan, Utah.

During normal communication, the data recorder sends an address together with a command to
the H-312 SDI-12 sensor. The H-312 then replies with a "response." In the following
descriptions, SDI-12 commands and responses are enclosed in quotes. The SDI-12 address and
the command/response terminators are defined as follows:

"a" Is the sensor address. The following ASCII Characters are valid addresses:

ATER

LOG® Series Model H-312 sensor. Included is a description of the

"0-9", "A-Z", "a-z", "*", "?". Sensors will be initially programmed at the
factory with the address of "0" for use in single sensor systems. Addresses
"1 to 9" and "A to Z" or "a to z" can be used for additional sensors
connected to the same SDI-12 bus. Address "*" and "?" are "wild card"
addresses which select any sensor, regardless of its actual address.

Notes:

"!" Is the last character of a command block.

"<cr><lf>" Are carriage return (0D) hex and line feed (0A) hex characters. They are

the last two characters of a response block.

• All commands/responses are upper-case printable ASCII characters.

• Commands must be terminated with a "!" character.

• Responses are terminated with <cr><lf> characters.

• The command string must be transmitted in a contiguous block with no gaps of more

than 1.66 milliseconds between characters.

H-312

SDI-12 Command and Response Protocol 4-1

4.1 Measure Command

The Measure Command causes a measurement sequence to be performed. Data values generated
in response to this command are stored in the sensor's buffer for subsequent collection using "D"
commands. The data will be retained in the sensor until another "M", " C", or "V" command is
executed.

Command
"aM!" "atttn<cr><lf>" Initiate measurement

Where:

a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

M is an upper-case ASCII character

ttt is a three digit integer (000-999) specifying the maximum time, in seconds,

n is a single digit integer (0-9) specifying the number of values that will be

Upon completion of the measurement, a service request "a<cr><lf>" is sent to the data recorder
indicating the sensor data is ready. The data recorder may wake the sensor with a break and
collect the data any time after the service request is received or the specified processing time has
elapsed.

Response Description

the sensor will take to complete the command and have measurement data
available in its buffer.

placed in the data buffer. If "n" is zero (0), no data will be available using
subsequent "D" commands.

Example of a H-312 "aM!" command:

Command

"aM!" "a0034<cr><lf>" 3 sec 4 Make measurement

Subsequent Command Response

"aD0" a+AA.AAA+BB.BBB+CC.C+DD.D<cr><lf>

Where:

AA.AAA = Stage (feet, inches, meters etc.)
BB.BBB = Pressure (PSI)
CC.C = Temperature (C)
DD.D = Sensor Supply Voltage (Volts)

4-2 SDI-12 Command and Response Protocol

Response Time Values Description

H-312

4.2 Concurrent Measurement Command

This is a new command for the Version 1.2 SDI-12 Specification. A concurrent measurement is
one which occurs while other SDI-12 sensors on the bus are also taking measurements. This
command is similar to the “aM!” command, however, the nn field has an extra digit and the sensor
does not issue a service request when it has completed the measurement. Communicating with
other sensors will NOT abort a concurrent measurement. Data values generated in response to
this command are stored in the sensor's buffer for subsequent collection using "D" commands.
The data will be retained in the sensor until another "M", "C", or "V" command is executed.

Command
"aC!" "atttnn<cr><lf>" Initiate measurement

Where:

a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").
C is an upper-case ASCII character
ttt is a three digit integer (000-999) specifying the maximum time, in seconds, the

sensor will take to complete the command and have measurement data available in
its buffer.

nn is a two digit integer (00-99) specifying the number of values that will be

placed in the data buffer. If "n" is zero (0), no data will be available using
subsequent "D" commands.

The data recorder may wake the sensor with a break and collect the data anytime after the
specified processing time has elapsed.

Response Description

H-312

SDI-12 Command and Response Protocol 4-3

4.3 Send Data Command

The Send Data command returns sensor data generated as the result of previous "aM!", "aC!", or
"aV!" commands. Values returned will be sent in 33 characters or less. The sensor's data buffer
will not be altered by this command.

Command

"aD0!" through "aD9!" "apd.d ... pd.d<cr><lf>"

Where:

a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

D0..D9 are upper-case ASCII characters.

p Is a polarity sign (+ or -)

d.d represents numeric digits before and/or after the decimal. A decimal may

be used in any position in the value after the polarity sign. If a decimal is
not used, it will be assumed to be after the last digit.

For example: +3.29 +23.5 -25.45 +300

If one or more values were specified and a "aD0!" returns no data (<CR><LF> only), it means
that the measurement was aborted and a new "M" command must be sent.

Example of a H-312 "aD0!" command:

Previous Command

"aM!" "a0034<cr><lf>"

Response

Response

Subsequent Command Response

"aD0" a+AA.AAA+BB.BBB+CC.C+DD.D<cr><lf>

Where:

AA.AAA = Stage (feet, inches, meters etc.)
BB.BBB = Pressure (PSI)
CC.C = Temperature (C)
DD.D = Sensor Supply Voltage (Volts)

4-4 SDI-12 Command and Response Protocol

H-312

4.4 Continuous Measurements

This is a new command for the Version 1.2 SDI-12 Specification. Sensors that are able to
continuously monitor the phenomena to be measured, such as a cable position, do not require a
start measurement command. They can be read directly with the R commands (R0!...R9!). The R
commands work exactly like the D (D0!...D9!) commands. The only difference is that the R
commands do not need to be preceded with an M command.

The H-312 does not
measurement and math operations require several seconds to complete..

4.5 Send Acknowledge Command

The Send Acknowledge Command returns a simple status response which includes the address of
the sensor. Any measurement data in the sensor's buffer is not disturbed.

Command

"a!" "a<cr><lf>"

Where: a Is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

support the aR0! continuous measurement commands because the

Response

H-312

SDI-12 Command and Response Protocol 4-5

4.6 Initiate Verify Command

The Verify Command causes a verify sequence to be performed. The result of this command is
similar to the "aM!" command except that the values generated are fixed test data and the results
of diagnostic checksum tests. The data generated in response to this command is placed in the
sensor's buffer for subsequent collection using "D" commands. The data will be retained in the
sensor until another "M", "C", or "V" command is executed.

Command
"aV!" "atttn<cr><lf>" Initiate verify sequence

Where:

a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

V is an upper-case ASCII character.

ttt is a three digit integer (000-999) specifying the maximum time, in seconds, the

sensor will take to complete the command and have data available in its buffer.

n is a single digit integer (0-9) specifying the number of values that will be

placed in the data buffer. If "n" is zero (0), no data will be available using
subsequent "D" commands

Example of a "aV!" command:

Command

"aV!" "a0013<cr><lf>" 1 sec 3 Return fixed data and diagnostic data

Response Time Values Description

Response Description

for testing purposes.

Subsequent Command

"aD0" a+123.456+78.9+y<cr><lf>

Key Description Units
+123.456 Fixed test data
+78.9 Fixed test data
y ROM checksum test 0 = Failed, 1 = Passed

4-6 SDI-12 Command and Response Protocol

Response

H-312

4.7 Send Identification Command

The Send Identification Command responds with sensor vendor, model, and version data. Any
measurement data in the sensor's buffer is not disturbed.

Command

"aI!" "allccccccccmmmmmmvvvxx...xx<cr><lf>"

Where:

a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

I is an upper-case ASCII character.

ll is the SDI-12 version compatibility level, e.g. version 1.2 is represented as

cccccccc is an 8 character vendor identification to be specified by the vendor and

mmmmmm is a 6 character field specifying the sensor model number.

vvv is a 3 character field specifying the sensor version number.

xx...xx is an optional field of up to a maximum of 13 characters to be used for serial

Response

"12".

usually in the form of a company name or its abbreviation.

number or other specific sensor information not relevant to operation of the
data recorder.

Example of a "aI!" command:

"a12 DAA H-312vvvS#nnnnnnVkkk<cr><lf>"

H-312 implementation of the optional 13 character field:

S#nnnnnnVkkk (12 bytes total)

Where:

"nnnnnn" is a six character sensor serial number
"kkk" is a three digit sensor firmware revision level

H-312

SDI-12 Command and Response Protocol 4-7

4.8 Change Sensor Address Command

The Change Sensor Address Command allows the sensor address to be changed. The address is
stored in non-volatile EEPROM within the sensor. The H-312 will not respond if the command
was invalid, the address was out of range, or the EEPROM programming operation failed.

Command
"aAn!" "n<cr><lf>" Change sensor address

Where:

a is the current (old) sensor address ("0-9", "A-Z", "a-z", "*", "?"). An ASCII

A is an upper-case ASCII character.

n is the new sensor address to be programmed ("0-9", "A-Z").

NOTE: To verify the new address use the "Identify Command."

Example of a "Change Sensor Address" command:

Command

"aA2!" "2<cr><lf>" Change sensor address to "2"

Response Description

"*" may be used as a "wild card" address if the current address is unknown
and only one sensor is connected to the bus.

Response Description

4-8 SDI-12 Command and Response Protocol

H-312

4.9 Extended Set_Current_Stage Command

The H-312 processes the pressure sensor input and computes Pressure in PSI units. Stage is
computed with a Stage = m * Pressure + b equation. During installation it is convenient to quickly
set the H-312's Stage reading to match the current stage or elevation of the water as determined by
a staff gauge or other datum. This command causes the H-312 to make a fresh measurement and
automatically update the Offset (b) term as needed to produce the desired Stage.

Example of a H-312 Extended "Set Current Stage" command:

Command

"aXSCS2.3!" "a0031<cr><lf>" 3 sec 1 Set the Stage to 2.3

Subsequent Command Response Description

"aD0" a+12.80<cr><lf> The new Offset

Response Time Values Description

H-312

SDI-12 Command and Response Protocol 4-9

4.10 Extended Read/Write Stage_Offset and Read/Write Stage_Slope

The H-312 processes the pressure sensor input and computes Pressure in PSI units. Stage is
computed with a Stage = m * Pressure + b equation. The Slope (m) and Offset (b) terms are
programmable, allowing the user to scale the reading into other engineering units. These
commands allow the user to read or write (change) the Stage_Slope and Stage_Offset terms. The
slope is set to 2.3067 and the offset to 0.00 at the factory. With the factory default (2.3067) the
Stage will be in units of water depth (in feet). The new values are stored in non-volatile EEPROM
within the sensor. Once the new Stage_Slope or Stage_Offset value is written to the EEPROM, a
copy is sent to the sensor data buffer for verification. This data can be viewed by using a
subsequent "D" command. To verify these settings any other time, use the "XRS" or “XRO”
commands. This command takes 001 seconds to complete and places 1 value in the data buffer.
Use the “aD0" command to collect and view the new slope or offset.

Command Response Description

"aXRS!" “a0011<cr><lf>" Read StageSlope
"aXRO!" “a0011<cr><lf>" Read StageOffset
"aXWSddd!" “a0011<cr><lf>" Write StageSlope
"aXWOddd!" “a0011<cr><lf>" Write StageOffset

Where: a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

XRS are upper case characters.
XRO are upper case characters.
XWS are upper case characters.
XWO are upper case characters.
ddd is the new slope or offset value (For example: 20.0, 195)

Example of a H-312 Extended "Read Stage_Slope" command:

Command Response Time Values Description

"aXRS!" "a0011<cr><lf>" 1 sec 1 Read StageSlope

Command

"aD0!" "a+1.00<cr><lf>" StageSlope is 1.00

Response Description

Example of a H-312 Extended "Write Stage_Slope" command:

Command Response Time Values Description

"aXWS1.234!" "a0011<cr><lf>" 1 sec 1 Write StageSlope

Command

"aD0!" "a+1.234<cr><lf>" StageSlope is 1.234

Response Description

4-10 SDI-12 Command and Response Protocol

H-312

4.11 Extended Read Mean_Count and Write Mean_Count

The H-312 makes multiple raw sensor measurements, discards the high and low values, integrates
(averages) the measurement data and computes Pressure (PSI). The number of raw sensor
measurements made for each SDI-12 measurement sequence is programmable. When measuring
turbulent water, tides or other special applications Mean_Count can be changed to increase or
decrease the number of pressure measurements made during the SDI-12 measurement sequence.

The H-312 makes 7-1/2 pressure measurements per second (133ms/ measurement). The ttt field in
the SDI-12 sensor response is computed by the H-312 and indicates how much time the H-312 will
require to complete the measurement sequence. The ttt field will automatically change if
Mean_Count is changed.

The H-312 comes from the factory with Mean_Count set to 16. The factory default ttt field is
computed internally by the H-312 as follows:

Raw Measurements: +2.13 sec (0.133 sec/measurement X 16 measurements)
Math Overhead: +0.3 sec
Round Upwards +1.0

- - - - - - -

ttt 3.0 Seconds

The “aXRMC!” and “aXWMC!” extended commands allow the number of raw sensor
measurements for each SDI-12 measurement sequence to be monitored or changed.

Once a new Mean_Count value is written, a copy is sent to the sensor data buffer for verification.
This data can be viewed by using a subsequent "D" command. To read or verify the value any
other time, use the "XRMC" command.

Command

"aXRMC!" “a0011<cr><lf>" Read Mean_Count
"aXWMCn!" “a0011<cr><lf>" Write Mean_Count

Where: a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").

XRMC are upper case characters.
XWMC are upper case characters.
n is the number of raw measurements wanted

This command takes 001 seconds to complete and places 1 value in the data buffer. Use the “aD0"
command to collect and view the current value.

Response Description

H-312

SDI-12 Command and Response Protocol 4-11

Example of a H-312 Extended "Read Mean_Count" command:

Command

"aXRMC!" "a0011<cr><lf>" 1 sec 1 Read Mean_Count

Command Response Description

"aD0!" "a+16<cr><lf>" Count = 16

Example of a H-312 Extended "Write Mean_Count" command:

Command

"aXWMC8!" "a0011<cr><lf>" 1 sec 1 Write Mean_Count

Command Response Description

"aD0!" "a+8<cr><lf>" Count = 8

Response Time Values Description

Response Time Values Description

4-12 SDI-12 Command and Response Protocol

H-312

4.12 Extended “XTEST”

This command is used for installation or production testing and requires the use of a H-419
Sidekick interface and a PC. This command causes the H-312 to transmit unsolicited real-time data
for testing purposes. The test mode is used to help troubleshoot the installation by providing a
continuous readout of pressure data. This is not compliant with the SDI-12 specification and is not
used with data loggers.

To activate the test mode, send the command “aXTEST!” from the PC. The H-312 will enter the
test mode and make continuous measurements. The test mode is exited by sending a break or any
new command on the SDI-12 bus. It may take a few tries to exit if the command is sent at the
same time data is being sent from the H-312. Removing power from the H-312 also causes it to
exit this mode.

Format:

SensorAdr + Stage + Pressure + Temperature +RawPressure (counts) + RawTemperature (counts)

“XTEST” displays the following data:

0: +1.202 +3.222 +23.0 +12345 +67890
0: +1.212 +3.232 +23.0 +12345 +67890
0: +1.222 +3.342 +23.0 +12345 +67890
0: +1.232 +3.352 +23.0 +12345 +67890
0: +1.232 +3.352 +23.0 +12345 +67890

etc.

H-312

SDI-12 Command and Response Protocol 4-13

4-14 SDI-12 Command and Response Protocol

H-312

Accuracy

(Maximum percent of error in measurement)
Pressure: Less than or equal to 0.05% of full scale

output (FSO) over temperature range
referenced to a straight line stretched
from zero PSI to maximum pressure

Temperature: Internal temperature ±1° C over

temperature range

Resolution

(Smallest change detectable in output signal)
Pressure: 1 part in 1,000,000 (0.0001%)
Temperature: 1 part in 1,000,000 (0.0001%)

Linearity

Less than 0.05% deviation from a straight line referenced to
end points

Pressure Hysteresis

Less than 0.02% of FSO

Long-term Stability

Accuracy drift is less than ±0.10% of FSO per year

Standard Ranges

Pressure Depth Accuracy
0 to 15 PSI 0 to 34.6 ft. ±0.017 ft.
0 to 30 PSI 0 to 69.20 ft ±0.035 ft.
Custom calibration ranges available from 5 to 75 PSI

Pressure Overload

Less than 2 times the rated pressure

Response Time

SDI-12: 3-second measurement sequence (programmable)

SDI-12 Output

Baud Rate: 1200
Protocol: SDI-12, 7-bit even parity, 1 stop bit
Output Voltage Levels:
Minimum high level: 3.5 volts
Maximum low level: 0.8 volts

Appendix A

H-312 Specifications

Media Compatibility

Liquids and gases compatible with PVC, ABS, RTV and
stainless steel. Polyurethane cable is not compatible with water
having high concentrations of chlorine.

Mechanical

Material: Corrosion proof, PVC and ABS plastic
Size 1.05 in. max diameter x 8.5 in. long
Pressure Port Stainless steel screen with 149 micron filter

(field replaceable)

Ballast: Stainless steel, 0.81 LB (0.36 KG)

Sensor Cable (Sensor to junction box):
Type: 4-conductor, 22awg, foil shield, internal

polyethylene vent, kevlar strength members, water-

block tape
Material: Polyurethane jacket
Diameter: 0.310" typ, .0.320" max

Dry Air System

Prevents moisture from condensing in the submersible pressure
transducer, provides compensation for changes in atmospheric
pressure without impairing the sensor’s accuracy. Periodic
maintenance is required.
Enclosure: Polycarbonate box with transparent lid
Desiccant: Indicating silica gel (field replaceable)

Warranty

The W

ATER

LOG® H-312 is warranted against defects in

materials and workmanship for one year from date of shipment.

Notes

Specifications subject to change without prior notice due to
ongoing commitment to product testing and improvement.
Design Analysis Associates, Inc. does not recommend the use of
submersible pressure transducers in surface water monitoring
applications where silt or mud are problematic.

Power Requirements

Voltage Input: 10 to 16.0 Volts DC
Supply Current:

Sleep Mode 150A max
Active (measuring) 50mA max
Surge Protection: Built in, 1.5 KVA

Environmental

Operating Temperature: 0° C to 40° C (non freezing)
Compensated Range: 0° C to 40° C
Storage Temperature: -10° C to 75° C

H-312

Specifications A-1

4-2 SDI-12 Command and Response Protocol

H-312

Appendix A

H-312-22 Specifications

Accuracy

(Maximum percent of error in measurement)
Pressure: Less than or equal to 0.02% of full scale

output (FSO) over temperature range
referenced to a straight line stretched
from zero PSI to maximum pressure

Temperature: Internal temperature ±1° C over

temperature range

Resolution

(Smallest change detectable in output signal)
Pressure: 1 part in 1,000,000 (0.0001%)
Temperature: 1 part in 1,000,000 (0.0001%)

Linearity

Less than 0.02% deviation from a straight line referenced to
end points

Pressure Hysteresis

Less than 0.01% of FSO

Long-term Stability

Accuracy drift is less than ±0.05% of FSO per year

Standard Ranges

Pressure Depth Accuracy
0 to 22 PSI 0 to 50.75 ft. ±0.01 ft.

Pressure Overload

Less than 2 times the rated pressure

Response Time

SDI-12: 3-second measurement sequence (programmable)

Liquids and gases compatible with PVC, ABS, RTV and
stainless steel. Polyurethane cable is not compatible with water
having high concentrations of chlorine.

Mechanical

Material: Corrosion proof, PVC and ABS plastic
Size 1.05 in. max diameter x 8.5 in. long
Pressure Port Stainless steel screen with 149 micron filter

(field replaceable)

Ballast: Stainless steel, 0.81 LB (0.36 KG)

Sensor Cable (Sensor to junction box):
Type: 4-conductor, 22awg, foil shield, internal

polyethylene vent, kevlar strength members, water-

block tape
Material: Polyurethane jacket
Diameter: 0.310" typ, .0.320" max

Dry Air System

Prevents moisture from condensing in the submersible pressure
transducer, provides compensation for changes in atmospheric
pressure without impairing the sensor’s accuracy. Periodic
maintenance is required.
Enclosure: Polycarbonate box with transparent lid
Desiccant: Indicating silica gel (field replaceable)

Warranty

The W

ATER

LOG® H-312-22 is warranted against defects in

materials and workmanship for one year from date of shipment.

Notes

Specifications subject to change without prior notice due to
ongoing commitment to product testing and improvement.

SDI-12 Output

Baud Rate: 1200
Protocol: SDI-12, 7-bit even parity, 1 stop bit
Output Voltage Levels:
Minimum high level: 3.5 volts
Maximum low level: 0.8 volts

Power Requirements

Voltage Input: 10 to 16.0 Volts DC
Supply Current:

Sleep Mode 150A max
Active (measuring) 50mA max
Surge Protection: Built in, 1.5 KVA

Environmental

Operating Temperature: 0° C to 40° C (non freezing)
Compensated Range: 0° C to 40° C
Storage Temperature: -10° C to 75° C

Media Compatibility

H-312-22

Design Analysis Associates, Inc. does not recommend the use of
submersible pressure transducers in surface water monitoring
applications where silt or mud are problematic.

Specifications B-1

4-2 SDI-12 Command and Response Protocol

H-312