Xylem H-3521 User Manual

Model

H-3521

Liquid & Gas Compatible Pressure Sensor

with SDI-12, 4-20mA and Modbus Outputs

Owner's Manual

Version 1.5

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

ATER

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:

LOG® Warranty

(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.

(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

H-3521

User Agreement/W

ATER

LOG® Warranty W-1

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

ATER

LOG® Warranty

H-3521

Table of Contents

User Agreement/W

Chapter 1 Introduction

1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1 Unpacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.2 Check The Model Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Chapter 2 Installation

2.1 Installing the W

2.2 Water Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.3 General Installation Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.4 Instrument Shelter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.5 Making Connections to the Pressure Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.6 Connecting Your Data Logger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.6.1 SDI-12 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

2.6.2 RS-232 Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

2.6.3 4-20mA Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

2.6.4 Modbus Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

2.7 Wiring and Installation Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.8 Programming Your SDI-12 Data Recorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.9 Programming the SDI-12 Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.10 Programming the H-3521 Fluid Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.10.1 Setting the Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

2.10.2 4-20mA Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

2.10.3 Programming the 4-20mA Output Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

2.11 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

ATER

LOG® Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . W-1

ATER

LOG® H-3521 Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Chapter 3 Maintenance/Troubleshooting

3.1 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2 Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.3 Offset Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.4 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Chapter 4 Simple Menu Interface

4.0 Simple Menu Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1 Connecting to the H-3521 Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2 General Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.3 Menu Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.1 P - Sensor Mode Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.2 V - Sensor Output Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.3 A - SDI-12 Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.4 S - Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.5 D - Digits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

H-3521

Table of Contents T-1

4.3.6 O - Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.7 U - Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.3.8 C - Averaged Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.3.9 M - Measure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.3.10 X - Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.4 Sensor Mode Options Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.4.1 P - Power Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.4.2 F - Fast Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.4.3 N - NOAA Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.4.4 R - Measure Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.4.5 D - Reset to Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.5 Sensor Output Options Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.5.1 Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.5.2 M - Max Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.5.3 N - Min Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.5.4 U - Update Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

Chapter 5 SDI-12 Command and Response Protocol

5.0 SDI-12 Command and Response Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.1 Measure Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5.2 Concurrent Measurement Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

5.3 Send Data Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5.4 Continuous Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

5.5 Initiate Verify Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

5.6 Send Identification Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8

5.7 Change Sensor Address Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

Extended SDI-12 Commands:

5.8 Extended Set Current Stage Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5.9 Extended Read/Write Offset and Read/Write Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11

5.10 Extended Read/Write Stage Digits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

5.11 Extended Read/Write 4-20mA_Hi and Read/Write 4-20mA_Lo . . . . . . . . . . . . . . . . . . 5-13

5.12 Extended Read Power_Mode and Write Power_Mode . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

5.13 Extended Read Measure Rate and Write Measure Rate . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

5.14 Extended Read Mean_Count and Write Mean_Count . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

5.15 Extended Read/Write NOAA Mode Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

5.16 Extended “XTEST” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

5.17 Extended “XDEF” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

5.18 Extended “XCFG” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

Appendix A Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Appendix B Modbus Protocol

B.1 Modbus Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

B.2 Modbus RTU Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

B.3 Modbus Function codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

T-2 Table of Contents

H-3521

B.4 Holding Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2

B.4.0 ID String(RO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2

B.4.1 Modbus Address(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2

B.4.2 Stage Units Select(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B.4.3 Reserved(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B.4.4 Modbus Baud rate(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B.4.5 Parity(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B.4.6 User Stage Offset(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B.4.7 User Stage Slope(R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B.4.8 Set Current Stage(WO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

B5 Input Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

B5.0 Stage(RO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

B5.1 Pressure(RO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

B5.2 Temperature(RO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

B5.3 Battery Voltage(RO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

H-3521

Table of Contents T-3

1.0 Introduction

Chapter 1

Introduction

The W
monitoring. The H-3521 directly measures water or other fluid pressure over a broad
temperature range. Typical applications include monitoring snow pillows to measure snow pack,
measurement of water in accumulating rain gauges, and fluid pressure in weirs and dams. The
H-3521 can be used in a gas-purge bubbler installation however, Design Analysis Associates,
Inc., manufactures other instruments specifically for that application.

The H-3521 has RS-232, SDI-12 and Modbus “smart” digital interfaces together with a 4-20mA
analog output. The sensor makes multiple pressure measurements, averages the results and
converts the measurement data into units of PSI, Feet, Meters or other engineering units.

The H-3521 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

ATER

LOG® H-3521 is a digital pressure transducer specifically designed for water level

(Use of H-423, SDI-12 to RS485 converter extends the range to 1000's of feet)
(H-4500 fiberoptic media converter works up to 1.2 miles)

The H-3521 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 has an atmospheric vent for compensation of barometric pressure changes
! Low current operation (less than 1 milliamp typical standby)
! Simple RS-232 menu interface for quick and easy setup.(No external module required)
! Outputs a 4-20mA signal.(no external module required)
! Extended SDI-12 commands for setting the Stage to the current water elevation.

H-3521

Introduction 1-1

1.1 Unpacking

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

! W
! Main interface cable
! RS-232 communications cable(optional)
! Owner's Manual

1.2 Check The Model Number

Before installing your new W
sensor 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:

ATER

LOG® H-3521 pressure transducer

ATER

LOG® H-3521, check the information on the label of the

S/N 1103
Range: 0-15 PSI (34.6' H20)
Output:: SDI-12, RS-232, Modbus, 4-20mA
Input: 10 to 16.0 Volts

This example shows that the W
to 15-psi.

1-2 Introduction

H-3521

Model

Fluid Pressure Sensor

ATER

LOG® H-3521 measures pressure within the range from zero

H-3521

Chapter 2

Installation

2.1 Installing the W

The W
monitoring. The H-3521 directly measures water or other fluid pressure over a broad
temperature range. Typical applications include monitoring snow pillows to measure snow pack,
measurement of water in accumulating rain gauges, and fluid pressure in weirs and dams. Before
proceeding with the installation, please consider several site preparation and maintenance issues:

ATER

LOG® H-3521 is a digital pressure transducer specifically designed for water level

ATER

LOG® H-3521

Figure 4 Sensor and Cable

2.2 Water Depth

The following chart shows the maximum pressure to which the H-3521 is factory calibrated. The
sensor can survive temporary operation up to twice the maximum rated pressure for you model’s
range. However, any measurements made beyond the rated pressure will be inaccurate. The H­3521 will be damaged if it is subjected to twice the maximum rated pressure.

Model Pressure Range Water Depth Range

H-3521-15 0 to 15 psi 0 to 34.60 ft. +0.01 ft

H-3521-30 0 to 30 psi 0 to 69.20 ft. +0.02 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 39.4EF.

*

Accuracy

H-3521

Installation 2-1

2.3 General Installation Recommendations

The H-3521 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-3521 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 in a heated shelter or are used with ethylene glycol or other antifreeze media.

2.4 Instrument Shelter

The sensor 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. Care
should be taken to place it where it will not be jarred or dropped, the H-3521 is a precision
instrument. Normally the H-3521 is mounted with the 4-corner feet on a level surface. Normally
the H-3521 is used to measure the hydrostatic head of a water source. The instrument should be
fastened to a gauge station shelf or fixed such that the elevation cannot accidently change.

Because the surface of the water being measured is exposed to atmospheric pressure, the pressure
sensor must provide correction for changes in barometric air pressure. To provide the best
accuracy possible, the H-3521 uses an atmospheric referenced pressure sensor design. The
internal pressure sensor in the H-3521 has a vent tube connected to the back side its pressure
diaphragm. The vent tube is routed to a sintered bronze filter next to the pressure port. Make
certain the gauge station enclosure is open to the atmosphere. If the sensor is placed in a cabinet
or sealed enclosure, the cabinet must have a screened vent or other opening to the atmosphere.

2-2 Installation

H-3521

2.5 Making Connections to the Pressure Port

The H-3521 has a 1/8" female NPT pressure port for making connections to your pressure source.
Apply Teflon tape or anaerobic thread dope to help prevent leaks. The pressure port has a
stainless steel plate to prevent the port fitting from spinning in the housing. Make certain the
“keeper” plate is in proper position. Whenever possible, use a backup wrench to avoid damaging
the enclosure. Before tightening the pressure port connection, bleed any air from the supply line.
Trapped air in the supply line will slowly dissolve into the water, as it does the density of the
water column changes from air to water and the pressure offset will drift.

Figure 5 Pressure & Vent Ports

H-3521

Installation 2-3

2.6 Connecting Your Data Logger

The H-3521 has RS-232, SDI-12 and Modbus “smart” digital interfaces together with a 4-20mA
analog output. The H-3521 is a SDI-12 V1.3 compliant sensor excluding the CRC commands. It
connects directly to any data recorder with SDI-12 capability. The instrument housing has both a
7 pin main interface connector and a 3 pin RS-232 communication connector.

Figure 6 Connector & Terminal Strip

7-pin Circular Connector 3-pin Circular Connector

Pin Color Function Pin Color Function

1

Orange

2

Brown

3

Blue

4

Green

5

Black

6

Red

7

Yellow

RS485+(Modbus)
RS485-(Modbus)
4-20mA+
4-20mA­GND
+12V Power
SDI-12 Data

1

N/A

2

N/A

3

N/A

RS232(TxD)
RS232(RxD)
GND

2-4 Installation

H-3521

2.6.1 SDI-12 Interface

The user must connect pins 5,6, and 7 to the data recorder or the user can power the H-3521
separate of the data recorder and connect just the SDI-12 data line(pin 7).

2.6.2 RS-232 Output

When the user wakes up the H-3521 with this port the H-3521 makes a new measurement and
updates the outputs (if enabled) and then prints out the measured stage and temperature value. If
the user sends a carriage return(CR) following the wake up then the H-3521 simple menu
interface is initiated and the H-3521 waits for a command. After 3 minutes of inactivity the
menu mode times out and the H-3521 returns to sleep.

2.6.3 4-20mA Output

Current loop sensors output a current rather than a voltage. The 4-20mA output will drive
standard industrial telemetry and process control instrumentation. Since the signal to noise
margin of 4-20mA is not large, take care to protect the wiring from noise and interference. The
loop power supply must be sufficient to maintain 8.5 to 35V across the H-3521's output
terminals, in addition to whatever voltage is needed to maintain 20mA across the loop receiver
and interconnect wiring. The +12.0V SDI-12 power source will work only if the resistance of
your loop receiver and wiring is less than 150 ohms.

8.5V + (150ohms * 20mA) = 11.5V

The 4-20mA output is reverse diode protected. The H-3521 is not loop powered, continuous
+12V instrument power must be supplied.

! Make certain there is 8.5 to 35V across the 4-20mA output terminals.
! Make certain the H-3521 is receiving +12V power.
! Use shielded 4-20mA cables in noisy environments.

2.6.4 Modbus Interface

Modbus is an industry standard serial digital interface for interconnecting Programmable Logic
Controllers (PLCs), intelligent sensors and other devices. The H-3521 is a Modbus slave and has
a serial RS-485 port for connecting to a Modbus compatible host device. See Appendix B for the
Modbus register definitions. Continuous +12Volt power must be supplied to the H-3521.

To activate the Modbus interface, issue an extended SDI-12 command or use the RS-232 menu
interface and set Power_Mode=4. See section 4/5 for details. This setting causes the H-3521 to
remain awake and monitor the RS-485 port for Modbus messages. This setting can be made at
the factory if requested.

H-3521

Installation 2-5

2.7 Wiring and Installation Precautions

! The H-3521 requires that the water be at ground potential. Mother Nature takes care of this

for surface and ground water.

! Make certain the pressure port connection is tight
! Make certain the sintered bronze vent port is not painted or covered

2.8 Programming Your SDI-12 Data Recorder

You must prepare your data recorder to receive and record the H-3521 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 are
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-3521 places four parameters in its data
buffer:

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

Where:

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 = Input Supply Voltage (Volts)

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-3521 comes from the factory with its address set to “0". The
address can be edited using the RS-232 menu interface or using an extended SDI-12 command.
Refer to chapters 4 and 5 for more details.

2.10 Programming the H-3521 Sensor

The H-3521 comes from the factory with the following programmable settings:

SDI Address: 0

Slope: 2.3067 (feet of H20)
Offset : 0.00
MeanCount: 16

Power_Mode: 0 (Sleep)

4-20ma_Hi: 20.0 (Ft)
4-20mA_Lo: 4.0 (Ft)

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-3521 and will not be lost if the power is disconnected. The extended
commands for changing these setups are described in detail in Chapter 5 and most of these

2-6 Installation

H-3521

settings can also be changed using the simple RS232 menu, see Chapter 4.

MeanCount is the number of raw pressure measurements averaged together to make one
measurement sequence. This setting determines how long the sensor will take to make a
measurement. MeanCount can be changed as described in chapters 4 and 5.

2.10.1 Setting the Stage

Many applications use the pressure sensor to measure water level in a gauge or reservoir. The
sensor translates water pressure to water level. When the H-3521 is first installed, you will want
to adjust the Offset such that the measurement data (Stage) corresponds to the current water
elevation or stage as determined with a staff gauge or other datum.

One of the ways to do this is by using the RS232 simple menu interface via Hyperterminal or
other similar terminal program. See chapter 4 section Connecting to the H-3521. Once you have
established connection your screen will look similar to the screen image below. When the user
sets the stage, the H-3521 makes a fresh measurement and automatically updates the Offset as
needed to produce the desired Stage. To set the stage using the RS-232 menu press ‘S’ for “S ­Stage:” and enter in the current stage value and then press enter. Then press the ‘M’ key for “M ­Measure” and verify that the set stage command did execute. You should see that the offset
value has changed. The other way to set the stage is to send the extended SDI-12 “Set Current
Stage” command. The “aXSCSdd.d!” command is discussed in more detail in section chapter 5.

H-3521

Installation 2-7

Example of a H-3521 Fluid Extended "Set Current Stage" command:

Command Response Time Values Description
"aXSCS2.3!" "a0061<cr><lf>" 6sec 1 Set the Stage to 2.3

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

2.10.2 4-20mA Output

The H-3521 has a 12-bit digital-to-analog converter (DAC), precision voltage reference and a 4­20mA current transmitter. The SDI-12 and 4-20mA sections are isolated from each other with a
high voltage digital opto-coupler. The Stage is scaled into a 12-bit value and loaded into the
digital-to-analog converter to control the current transmitter. The 4-20mA output is updated
whenever a measurement is made. If no measurements are made, the 4-20mA output becomes
“stale”. For industrial applications where the H-3521 is connected to a SCADA or PLC system
instead of a SDI-12 data logger, the H-3521 can be programmed to automatically make
continuous measurements. To program the H-3521 to make continuous measurements, issue an
extended SDI-12 command and set Power_Mode=3. See Chapter 4 for details. This setting can
be made at the factory if requested.

Note: When the H-3521 is first powered up, the output current is set to 4.0mA. It remains at

4.0mA until the first measurement sequence. The digital-to-analog converter is powered from

the loop side of the opto-isolator. If the loop power is disconnected or is applied after the SDI-12
side is powered up, the data in the digital-to-analog converter will be lost. When the loop power
is restored, the 4-20mA output will be at an unknown value. Once a fresh SDI-12 measurement
is made, the digital-to-analog converter is loaded with new valid data.

2.10.3 Programming the 4-20mA Output Range

The H-3521 scales the current Stage data to drive the 4-20mA output. The 4-20mA_Hi and 4­20mA_Lo settings control how the Stage data is processed. The 4-20mA_Lo should be set to the

desired Stage corresponding a 4.00mA output. The 4-20mA_Hi should be set to the desired Stage
corresponding to a 20.00mA output. For testing purposes, the H-3521 comes from the factory
with 4-20mA_Hi = 20.0 and 4-20mA_Lo = 4.00. See Chapter 4 for details on programming these
settings. The extended “aXS!” command allows convenient testing of the 4-20mA output. This
command allows the user to temporarily force the Stage to a test value. For example, the user
can force the Stage to several different values while calibrating or monitoring the attached 4­20mA instrumentation. Once a fresh measurement is made via a SDI-12 measurement , the
temporary Stage data is overridden.

2-8 Installation

H-3521