UniData Communication Systems 6541 User manual

Manual – Precision Water Level Instruments – Model 6541
Unidata Manual - 6541 Precision Water Level Instruments Issue 2.1
Manual
Precision Water Level Instruments
Model 6541
Revision History
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Previous version BX 2004 RS/ JH
Unidata Manual - 6541 Precision Water Level Instruments Issue 2.1 2007 AB/CB/JH/MS/KC
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Manual – Precision Water Level Instrument
Unidata Manual 6293 - Precision Water Level Instruments Issue 2.1
Picture of the Water Level Instrument

Precision Water Level Instrument
Unidata Manual 6293 - Precision Water Level Instruments Issue 2.1 i
CONTENTS
16541B WATER LEVEL INSTRUMENT ......................................................................1
1.1 SUPERSEDED INSTRUMENTS ........................................................................................ 1
1.2 MANUAL ORGANISATION ............................................................................................ 1
2APPLICATIONS..............................................................................................................2
2.1 USING THE 6541.......................................................................................................... 2
2.2 FEATURES ................................................................................................................... 3
2.3 OPERATING MODES..................................................................................................... 4
2.4 MODELS ...................................................................................................................... 5
2.5 MODEL 6541B WITH MICROLOGGER........................................................................... 6
2.6 OUTPUT OPTIONS ........................................................................................................ 6
2.7 MOUNTING AND INSTALLATION OPTIONS ................................................................... 7
2.8 FLOAT SYSTEMS.......................................................................................................... 7
2.9 MICROLOGGER OPTIONS ............................................................................................. 8
3LOGGING DATA............................................................................................................9
3.1 CREATING A SCHEME FOR YOUR PROJECT .................................................................. 9
3.1.1 Adding an Instrument to a Scheme.........................................................................9
3.1.2 When to Log .........................................................................................................11
3.1.3 What to Log..........................................................................................................12
4PREPARING FOR INSTALLATION.........................................................................14
4.1 CONTROLS AND SETTINGS......................................................................................... 14
4.2 CONNECTING A BATTERY PACK ................................................................................ 14
4.3 CONNECTING TO AN EXTERNAL DATA LOGGER VIA HSIO ....................................... 15
4.3.1 HSIO Interfaces....................................................................................................16
4.4 CONNECTING MORE THAN ONE INSTRUMENT TO A LOGGER .................................... 16
4.5 SDI-12 INTERFACE.................................................................................................... 16
4.5.1 Wiring Connections..............................................................................................17
4.5.2 Commands............................................................................................................17
4.6 CURRENT LOOP INTERFACE (4-20MA). ..................................................................... 18
4.6.1 Wiring Connections..............................................................................................18
4.6.2 Span & Zero Configuration..................................................................................19
4.7 HSIO INTERFACES. ................................................................................................... 20
4.8 CONNECTING MORE THAN ONE INSTRUMENT TO A LOGGER .................................... 20
4.9 BENCH TESTING THE INSTRUMENT SYSTEM .............................................................. 21
5SITE INSTALLATION.................................................................................................22
5.1 INSTALLING THE INSTRUMENT IN THE RECORDING POSITION.................................... 22
5.2 INSTALLING THE FLOAT SYSTEM............................................................................... 22
5.3 SETTING THE INSTRUMENT WATERLEVEL ................................................................. 23
66541 APPLICATIONS...................................................................................................24
6.1 MEASURING SURFACE WATER LEVELS..................................................................... 24
6.2 MEASURING FLOW IN OPEN CHANNELS .................................................................... 24
6.3 MEASURING GROUND WATER LEVELS ..................................................................... 24

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6.4 FLOATWELL DESIGN FOR WATER LEVEL MEASUREMENT......................................... 25
6.5 MEASURING RAINFALL ............................................................................................. 25
6.6 MEASURING PAN EVAPORATION ............................................................................... 26
6.7 FLOATWELL DESIGN FOR WATER LEVEL MEASUREMENT......................................... 26
6.8 SOURCES OF ERROR IN FLOAT SYSTEMS ................................................................... 26
6.9 CAUSES OF ERROR .................................................................................................... 27
7SPECIFICATIONS: MODEL 6541 INSTRUMENT .................................................28
8APPENDIX A - 6541L MICROLOGGER...................................................................29
8.1 SPECIFICATIONS ........................................................................................................ 29
8.2 MOUNTING ................................................................................................................ 29
8.3 SIGNAL CONNECTIONS .............................................................................................. 30
8.4 OTHER CONNECTORS ................................................................................................ 31
8.5 THE USER POWER SUPPLY (UPS).............................................................................. 31
8.6 REGISTER ALLOCATION ............................................................................................ 32
8.7 FIELD INSTALLATION ................................................................................................ 33
8.8 6541S/B 4-20MAOPTION ......................................................................................... 33
9APPENDIX B - DETAILS OF UNIDATA FLOAT SYSTEMS................................34
9.1 FLOAT LINES ............................................................................................................. 34
9.2 FLOATS ..................................................................................................................... 34
9.3 FLOAT PULLEYS ........................................................................................................ 37
9.4 FLOAT SYSTEM ACCESSORIES ................................................................................... 37
10 APPENDIX C - FLOAT SYSTEMS.............................................................................38
10.1 INTRODUCTION TO FLOAT SYSTEMS.......................................................................... 38
10.2 SOURCES OF ERROR IN FLOAT SYSTEMS ................................................................... 38
10.3 CAUSES OF ERROR .................................................................................................... 38
10.3.1 Float Line Shift.................................................................................................39
10.3.2 Submergence of Counterweight .......................................................................39
10.3.3 Instrument Lag ................................................................................................. 39
10.3.4 Temperature Change........................................................................................40
10.3.5 Coefficients of Expansion.................................................................................40
10.3.6 Correction Formulae........................................................................................40
10.3.7 Example............................................................................................................41
10.4 REDUCING ERRORS ................................................................................................... 41
11 APPENDIX D – FLOATWELLS .................................................................................42
11.1 THE NEED FOR FLOATWELLS .................................................................................... 42
11.2 FLOATWELL DESIGN ................................................................................................. 42
11.3 MOUNTING THE INSTRUMENT ON A FLOATWELL....................................................... 43
11.4 MEASURING LOCATION............................................................................................. 43
11.4.1 Water Velocity..................................................................................................43
11.4.2 Siltation ............................................................................................................44
11.4.3 Environmental impact......................................................................................44
11.4.4 Access and Security..........................................................................................45
11.5 OTHER FEATURES OF A FLOATWELL SITE ................................................................. 45

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1 6541B WATER LEVEL INSTRUMENT
The 6541B is a float operated precision water level instrument. Float-operated
instruments can be the most accurate way to monitor the level of a water
surface. The Unidata Model 6541B Precision Water Level Instrument can
achieve an operating accuracy and resolution of 0.1mm. This accuracy is
maintained for the service life of the instrument without calibration or
maintenance, apart from battery changes. The instrument has the range to
monitor surface and underground waters, and the precision to monitor rainfall
and evaporation. This Model 6541B instrument supersedes the Unidata Model
6541A instrument.
The instrument is normally connected to the water surface by a float system. As
the water level changes, this rotates the input shaft on which is mounted an
optical encoder. The encoder is continuously monitored and the instrument
tracks any water level changes updating the level displayed on the LCD display.
The very low mechanical friction and inertia of the instrument produce data of
high precision and accuracy. A replaceable battery pack powers the instrument
for more than 1 year.
1.1 Superseded Instruments
The 6541B instrument supersedes the UNIDATA Model 6541A, 6509, 6531
instruments. For further information see the manuals for these products.
1.2 Manual Organisation
Throughout this manual the model number 6541 will be used when describing
features common to all the 6541 family of instruments.
When describing features specific to an individual model of the 6541 family, the
model number will be used. For example: 6541B-11-C.

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2 APPLICATIONS
The 6541series instruments can be used to monitor water level in a diverse range of
conditions. Typical applications include monitoring water level in:
•Rivers, streams, canals, channels, sewers and drains ⎯flow measurement.
•Reservoirs and lakes ⎯management and water supply.
•Bores, piezometers, springs and soaks ⎯aquifer studies and management.
•Harbours and estuaries ⎯tidal and coastal hydrology studies.
•Rainfall captured in measuring tanks ⎯long term precipitation data.
•Evaporation from measuring pans ⎯automatic evaporation monitoring.
The float pulley can be changed to vary the units and resolution of the
measurement.
2.1 Using the 6541
The 6541 is simple to install and use. At installation all adjustments are made using
the switches located inside the front cover. Each instrument has a LCD display that
shows the water level reading and updates automatically as the water level changes.
The instrument is powered by an internal pack of alkaline batteries with a service
life of more than 12 months. The LCD will flash “Lo Batt.” when the battery pack
nears full discharge and requires replacement.

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2.2 Features
Most wiring connections to the 6541B Water Level Instrument are made by the
front panel screw terminals.
Power Supply. The instrument can be powered either from a Unidata battery pack
plug or, via flying leads from an external power source.
HSIO. Access to a 4 wire plus ground Unidata HSIO interface is provided
by the front panel terminals. A “data in” terminal allows extension
of a HSIO instrument chain.
SDI-12. These terminals provide a connection point for the Version 1.3
compliant SDI-12 interface.
Current Loop. The 4-20mA current loop is a 3 wire optically isolated interface. It
requires that the loop power be supplied by the logger end of the
loop. Note: The base level 6541B instrument is not fitted with the
current loop interface.

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2.3 Operating Modes
The operating modes of the 6541B WLI are set using the 8 DIP switches on the
front panel.
Switch Function Off On
1 DIR (Pulley Dir.) Clockwise Counter Clockwise
2 PULLEY (Metric Pulleys)1500mm / 1ft pulley 100mm pulley
3 UNITS (of measurement) mm Feet x.xx
4 FSD (Full Scale Deflection) Max. Count265535 299999
5 MODE SDI-12 Future option
8 POWER Instrument Off Instrument On
Note 1: The current loop interface will only work with a maximum count setting of 65535. The
299999 (4 FSD) setting cannot be used for HSIO please use 5 SDI-12 instead.
Note 2: Pulley size & resolution
Pulley Circumference Resolution
100mm 0.1mm
500mm 1mm
1 foot 0.01’
In general there are three ways of using the 6541...
With no data logger -
As a water level measurement and display instrument the water level can be
observed on the LCD display but measurements are not stored.
With an Internal Data Logger -
As a water level measurement and display instrument with a built-in data logger –
the 6541-nnn/C that can measure up to three additional external parameters.
With an External Data Logger -
As a water level measurement and display instrument, with an external data
acquisition facility such as a UNIDATA STARLOGGER. This is required when
you need to measure many external parameters.

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2.4 Models
The Model 6541 Instrument can be supplied in a number of versions to suit
different applications. Versions are indicated by a three digit code appended to the
instrument model number.
The example below shows the instrument with:
A 500mm pulley, alkaline battery and UNIDATA Micrologger fitted.
Config
Model 6541B-0
Model 6541B-1x
Model 6541B-2x
Model 6541B-3x
No pulley wheel.
500mm circ. pulley, metric, 1mm res.
1 foot circ. float pulley, Imperial, 0.01ft res.
100mm circ. float pulley, metric, rain, 0.2mm res.
Battery
Model 6541B-x0
Model 6541B-x1
No battery.
UNIDATA Model 6910A Alkaline Battery Pack.
Logger
Model 6541B-xx
Model 6541B-xx-C
Without Micrologger fitted.
With Micrologger fitted.
Note: For Model 6541B-CL 4-20mA Output – contact factory.
Battery
Pulley Size
Logger / No Logger
6541B-11-C

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2.5 Model 6541B with Micrologger
To specify the internal Micrologger, add -C to the 6541B version you select.
2.6 Output Options
The instrument has three output interface options:
SDI-12 Interface.
The 6541B Water Level Instrument has a Version 1.3 - compliant SDI-12 sensor
interface. The 6541B is powered all the time and measurements are instantaneously
available allowing the use of the aR0! commands. The CRCed version of this
command is also valid.
HSIO Interfaces
The 6541B has Primary and secondary interfaces. The secondary HSIO interface is
intended for connection to a Micrologger. When fitted with a Micrologger the
6541B becomes a standalone logging instrument.
4-20 mA signal Population Option
This will produce an analog signal suitable for current loop instruments used in
process control systems. The measurement range of the instrument is fully user-
programmable over the output range.

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2.7 Mounting and Installation Options
Available mounting options help simplify your installation and adapt the instrument
to different applications.
Mounting Adapter Plates
These can be bolted to the base to allow the 6541 to mount on the same holes as the
superseded 6509.
Offset Pulley
These attach to the instrument mounting bracket to guide the float line to hang
correctly inside the float well. They are not normally used as the added friction
reduces the system sensitivity.
2.8 Float Systems
UNIDATA can supply the float systems required for accurate operation at your site.
A range of float systems can be supplied. All float systems have associated errors.
These are minimised by using the largest float that is practical. See Appendix C for
more details of float systems.

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2.9 Micrologger Options
The Micrologger is a factory fitted option that mounts within the water level
instrument housing. When you use a Micrologger you do not require an external
data logger to store water level measurements over time. The Micrologger has most
of the features of a UNIDATA STARLOGGER and is operated in the same way
using the same software as all other UNIDATA loggers.
The 6541B-nn-C instrument incorporates the UNIDATA 6541L Micrologger. See
Appendix A for details.
Water level is measured using the Micrologger’s high speed serial IO channel. The
Micrologger has two analogue inputs and two digital and inputs. Its also has a
counter input. You can use these inputs to measure other physical parameters such
as rainfall, water or air temperature, barometric pressure and wind direction.
The 6541L Micrologger also includes one open collector output that can control an
external device.
You should use the 6541-nn-C when you need to measure water level and a couple
of other physical parameters.
The 6541B-L Micrologger is program-compatible with UNIDATA data loggers.

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3 LOGGING DATA
With the 6541 Precision Water Level Instrument connected to a STARLOGGER
or PROLOGGER or, when using the 6541-nn-C internal Micrologger; the water
level sensed by the instrument is logged and stored according to a data logging
program (called a Scheme), defined within the STARLOG Software Package.
The Windows-based STARLOG Software Package enables you to create a
scheme and then download it to the STARLOGGER, PROLOGGER or
Micrologger.
The STARLOG User Manual describes use of the Software Package.
3.1 Creating a Scheme for Your Project
A Scheme has to be loaded into each UNIDATA logger. Schemes are generally
unique to a site or project.
The scheme instructs the logger:
•What instruments are connected
•How and when to log the data
•How to scale the acquired data
•How to format the output (defined as reports in the scheme).
3.1.1 Adding an Instrument to a Scheme
As the 6541B is a new instrument, you may need to add it to the Instrument
Library in your software. In the Scheme Editor, click the Instruments icon.
This will display the Scheme Instruments window.
Select an Instrument Library, then view the instruments listed. If this model of
instrument does not appear in your instrument list(s), you may add it by clicking
the New button.
The new instrument will be shown as User
#1-User defined instrument. Double-click it
to open the Instrument Setup screen.
You can now enter a name and description
for the instrument, allocate a channel, the
scaling factors, and other setup details.

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If you are using an existing instrument from one of the libraries, then double-
clicking on it from the Scheme Editor will allow you to check and adjust the
scaling details appropriate to the instrument(s) in use.
Model 6541-1 Metric Water Level with 500 mm Pulley
(used for general measurements)
More examples of setup for alternative pulley diameters are shown below.
When you have finished entering or adjusting the instrument details, click the
[Ok] button.
If you choose to log data via a channel other than the default (channel S0),
ensure the 6541 is connected to the correct terminal on the Field Termination
Strip if you are using one, or the correct pin in the INPUT SIGNALS connector
if you are connecting directly to a STARLOGGER. See your logger manual for
details.
The connections described in this manual assume:
•In the case of STARLOGGER and PROLOGGER connection, you are
using the default serial channel, S0. Note that up to eight 6541 instruments
can be connected to a data logger. If you want to connect more than one
instrument nominate a different serial channel for each instrument.
•In the case of the 6541-nn-C (Micrologger version) see Appendix A.
Model 6541-2 Imperial Water
Level with 12 Inch Pulley
(used for general measurements)
Note that the data logged for
units of feet is in feet and tenths
of feet, not feet and inches. For
example 2.5 feet, is not 2 feet 5
inches.

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Model 6541-3 Metric Water Level with 100mm Pulley
(used for precision measurements)
3.1.2 When to Log
When you log data you save it in the memory of the logger. This is the
information that you record for later use. You can select what data to log, and
when to log it, so the time series of data that you capture will suit your project
and application. This is often a compromise between the memory size of the
logger, the data detail that you wish to record, and how often you can unload
and process the data.
The logger will read the 6541 at the scan intervals you select. You have the
option of time based logging (e.g. each 15 minutes), event based logging (e.g.
each time the water level changes 5mm) or a combination of time and events
(say once each day and each time the level changes 10mm).
Time Based Logging
The default method is time based logging and this is typically used for water
level measurement. The logging interval must suit the site conditions and
project. For reservoirs and groundwater aquifers, water level may change
slowly. In such cases logging the average water level each hour may be
adequate. In larger rivers logging each 15 minutes may be suitable. The water
level in smaller streams and drains can change rapidly and you may need to log
each 1 to 5 minutes to capture the maximum rates of change that can occur. For
rainfall or evaporation you may require hourly or daily totals or you may wish to
log detailed data from which you can derive maximum rainfall intensities
needed for design studies.
When you use Time Based Logging, memory usage is consistent and the time
and date when the memory will be full can be predicted.
Three parameters define the time element of the logged data:

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•Scan rate.
•Log interval.
•Log sub-interval.
The scan rate defines the frequency at which the logger “wakes-up” and
interrogates the instrument. This is typically 5 seconds, however a shorter
interval may be defined for better data definition or, a longer interval to
conserve data logger battery power.
The log interval is the time between entries saved to the logger memory. The
ideal log interval will capture adequate details for your project without wasting
memory or producing unnecessary data.
Natural water levels may change slowly for most of the time except during very
intense rainfall when rapid changes may occur. For many projects you will want
to record these extreme events and will need to select your log interval
accordingly. Key in the log interval. It must equal an even number of scans.
Logs will be aligned to logical real times, e.g. hourly data will log on the hour.
The sub-interval allows you to average data over a portion of the log interval.
For example, if you have selected a log interval of 1 hour and you enter a sub-
interval of 5 minutes, the data you log (if you select (ave)) will be the average of
all scans in the last 5 minutes of the log interval.
Event Based Logging
You can also define an event-based scheme. Event-based logging can extend the
memory endurance by only logging when specific events are detected. A simple
example of an event is; to log each time there is a level change greater than
5mm.
Water surfaces fluctuate by small amounts constantly. Avoid defining small
increments (say 1mm) or the logger memory will be quickly exhausted.
Events are defined in the Event window. Each time a defined event occurs, the
time, date and instrument value is logged.
Memory use depends on the rate at which the events occur. As a result memory
use cannot be predicted with certainty when you use Event Based Logging.
3.1.3 What to Log
You specify what data is logged by checking the boxes for each instrument
channel in the log buffer window, as shown on the next page.
The logging options are as follows:

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The data from the last scan (RAW),
The average of some (ave) or all (AVE) scans or,
The maximum (MAX) or,
The minimum (MIN) scan
For example, with a time based scheme you may want to log the average value
of all scans, and also the maximum during each log period.
Averaging data has the effect of smoothing out minor variations. It is a useful
way of eliminating spikes caused by waves or ripples. Logging an average over
a long period, say one hour, may de-sensitise the data. Using the sub-interval of
say one minute would log the average of the last 1 minute of data in each hour.
Simply select as many log actions as required by checking the box in each
required column on the line next to the instrument’s channel.
Save the scheme you have created, using a name to suit the site or project.

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4 PREPARING FOR INSTALLATION
This section describes:
•The instrument options.
•How to connect the instrument to an external UNIDATA logger.
•How to test the system.
You should assemble and bench test a new system before installing it on site. Testing
should include the logging and recovery of a period of data. This will allow you to
confirm satisfactory operation of the entire system and for the site operators to
become familiar with the instruments and software.
4.1 Controls and Settings
All the controls you need to install and operate the 6541 are accessed by removing
the front cover.
The factory default switch settings are:
•Display counts up.
•Counts in (1mm) metric increments.
•Operates normally.
•Internal battery is OFF.
4.2 Connecting a Battery Pack
Plug in a model 6901B Battery pack to the socket located on the left-hand side.

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4.3 Connecting to an External Data Logger via HSIO
Removing the front cover reveals a termination block to which the data logger cable
is connected. This cable exits through the gland in the side of the instrument.
External power may be connected to the designated terminals.
Precision Water Level Instrument STARLOGGER Prologger
Wire
Colour Logger Function Pin Term Pin Term
Red +5.00V DC sync (terminal 3) 13 15, 16 or 17 18 14
Green (terminal 7) 23 14 28 17
Blue DATA IN (s0) (terminal 5) 21 11 32 11
White DATA OUT (terminal 6)
Yellow Serial CLOCK (terminal 4) 9 12 14 12
Notes
Pin # refers to the pins of the INPUT SIGNALS connector on a logger.
Term # refers to numbered screw terminals on a Field Termination Strip. This is the
connection method you are most likely to use.
1Refer to the supplement included with your logger or Field Termination Strip for
more information about these connections.

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4.3.1 HSIO Interfaces.
The 6541B has two HSIO interfaces. The primary interface is accessible via the
screw terminals at the front of the instrument. The secondary HSIO interface is
accessed by the IDC header located low on the rear of the PCB and is intended for
connection to a Micrologger. When fitted with a Micrologger the 6541B becomes a
standalone logging instrument.
The HSIO interface wiring shall be configured as below:
4.4 Connecting More Than One Instrument to a Logger
Each serial channel on a STARLOGGER or PROLOGGER will support up to eight
“daisy-chained” instruments. The first encoder’s DATA IN (blue wire) connects to
the logger’s serial channel input (S0); the second encoder’s DATA IN (blue wire)
connects to the first encoder’s SERIAL LINK (white wire, S1) and so on.
The +5V DC (red), COMMON (green) and SERIAL CLOCK (yellow) signals must
be connected in parallel at the logger or the adjacent encoder’s terminal block if that
is more convenient.
4.5 SDI-12 Interface.
The 6541B Water Level Instrument has a Version 1.3 - compliant SDI-12 sensor
interface. As the 6541B generally has its own battery power source, only two wires
are required for the sdi-12 communications. These are GND and SDI-12 for the data.
Generally sdi-12 sensors are not continuously powered and upon receipt of an sdi12
command they need some time to take their measurements before reporting these
measurements back to the recorder. The 6541B is powered all the time and
measurements are instantaneously available allowing the use of the aR0! commands.