Impact Subsea ISA500 User manual

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T. [phone]
Impact Subsea Ltd, Company Number: SC498003, Registered in Scotland, Registered
Office: Unit 10, Castle Street, Castle Road Industrial Estate, Ellon, AB41 9FR, UK
E. [email protected]k
W. www.impactsubsea.com
ISA500
Altitude Sensor
With optional integrated AHRS
Installation & Operation Manual
Revision Number:
2.0
Date
8th July 2020

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1.0 Introduction ........................................................................................................................3
2.0 Specification.........................................................................................................................4
2.1 Overview...........................................................................................................................4
2.2 Dimensions .......................................................................................................................4
2.2.1 Forward Looking Housing......................................................................................4
2.2.2 Right Angle Housing ..............................................................................................4
2.3 Acoustic, Heading, Attitude & Temperature....................................................................5
2.4 Communications, Power & Physical.................................................................................5
3.0 Installation ..........................................................................................................................6
3.1 Electrical Installation ........................................................................................................6
3.1.1 Connector Pin Out......................................................................................................6
3.1.2 Power .........................................................................................................................7
3.1.3 Serial Interface...........................................................................................................7
3.1.4 RS232 Wiring..............................................................................................................7
3.1.5 RS485 Wiring..............................................................................................................8
3.1.6 Analogue Out and TTL Trigger ...................................................................................8
3.1.7 Establishing Communications....................................................................................9
3.1.8 Connector Mating ......................................................................................................9
3.1.9 Connector Cleaning....................................................................................................9
3.2 Location ..........................................................................................................................10
3.2.1 Acoustics (Altitude Measurement Performance) ....................................................10
3.2.2 Magnetic Disturbers (Heading Performance)..........................................................10
3.2.3 Alignment with Vehicle (Pitch/Roll Accuracy) .........................................................11
3.2.4 Heat Sources (Temperature Accuracy) ....................................................................11
3.3 Mounting ........................................................................................................................12
4.0 Operation...........................................................................................................................13
4.1 Use with seaView software ............................................................................................13
4.2 Integration with Systems................................................................................................14
4.3 Understanding advanced features .................................................................................14
5.0 Servicing............................................................................................................................16
6.0 Output Strings...................................................................................................................17
6.1 Altitude ...........................................................................................................................17
6.2 AHRS ...............................................................................................................................24

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7.0 Theory of Operation..........................................................................................................26
7.1 Altitude - Basic Principles ...............................................................................................26
7.2 The Sonar Equation ........................................................................................................27
7.2.1 Source Level (SL).....................................................................................................28
7.2.2 Transmission Loss (TL)............................................................................................28
7.2.3 Noise Level (NL)......................................................................................................28
7.2.4 Directional Index (DI) .............................................................................................29
7.2.5 Detection Threshold (DT).......................................................................................29
7.3 Heading, Pitch & Roll......................................................................................................30
7.4 Temperature...................................................................................................................30
8.0 Warranty ...........................................................................................................................31
9.0 Technical Support .............................................................................................................32

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1.0 Introduction
The ISA500 provides exceptionally accurate and long-range underwater distance measurement
capability. Optionally the ISA500 can also provide Heading, Pitch, Roll and Temperature
readings.
Designed to measure distance to the seabed (as an underwater Altimeter) the ISA500 can also
be used in a number of underwater applications where a distance requires to be measured or
monitored.
Utilising a broadband composite transducer and advanced digital signal processing techniques;
enables the ISA500 to achieve long range capability with a high degree of accuracy and stability.
The availability of heading, pitch and roll provides the capability to clearly understand the
orientation of the unit at all times. This can also be used to automatically correct slant range
readings; providing a true altitude measurement if required. Alternatively, these sensor
readings can be used for navigation purposes of a ROV, AUV or other underwater items.
Housed in a compact titanium or lightweight acetal housing and available in forward looking
and right angle housing configurations; ensures that the ISA500 is not only at the forefront of
sensor technology, but is built to withstand the most extreme underwater environments.
ISA500 (Forward Looking Titanium Housing)
ISA500 (Right Angle Acetal Housing)

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2.0 Specification
2.1 Overview
ISA500 (Forward Looking Titanium Housing) ISA500 (Right Angle Acetal Housing)
2.2 Dimensions
2.2.1 Forward Looking Housing
2.2.2 Right Angle Housing
All dimensions are in mm.
All dimensions given in mm.

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2.3 Acoustic, Heading, Attitude & Temperature
Acoustic
Attitude
Frequency
500kHz Standard
(400 to 600kHz Selectable)
Pitch Range
± 90°
Roll Range
± 180°
Range
0.1 to 120+m
(Maximum range dependant on
seabed type: Ranges in excess of
175 meters are achievable with a
strong acoustic reflector)
Accuracy
0.2°
Resolution
1mm
Resolution
0.1°
Beam Angle
6° conical at 500kHz
Temperature
Signalling
Monotonic
Accuracy
0.5°
Pulse Length
User Defined
Resolution
0.1°
Heading
Accuracy
± 1°
Resolution
0.1°
2.4 Communications, Power & Physical
Communications & Power
Physical
Digital
RS232 & RS485
F/L: Weight (Air/Water)
R/A: Weight (Air/Water)
0.5 / 0.325kg (Titanium)
0.3 / 0.11kg (Acetal)
0.52 / 0.35kg (Titanium)
0.325 / 0.125kg (Acetal)
Protocol
300 to 115200 baud
Depth Rating
6,000 meters (Titanium)
1,000 meters (Acetal)
(11,000 meter option
available)
Analogue
0 to 5 V DC or
0 to 10V DC or
4-20mA
Temperature
Operating: -10 to 40°
Storage: -20 to 50°
Data
Continuous or on
demand
Connector
Subconn MCBH8M-SS fitted
as standard
Data Rate
Up to 10Hz
* 100% Tx power, 10Hz update rate
Input Voltage
9 to 36V DC
Power (No Altitude)
25mA @ 24V DC
Power (With Altitude)
51mA @ 24V DC *

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3.0 Installation
3.1 Electrical Installation
The ISA500 is fitted with a SubConn MCBH8M-SS connector as standard. This will mate to a
SubConn MCIL8F connector/cable assembly.
3.1.1 Connector Pin Out
The standard connector pin out is provided below:
Male Connector on ISA500 Unit
Pin
Function
Mating Wire Colour
1
0VDC
Black
2
9-36VDC
White
3
Analogue Out
Red
4
0V Analogue
Green
5
0V Digital
Orange
6
Trigger
Blue
7
RS232 TX & RS485 A+
White/Black
8
RS232 RX & RS485 B-
Red/Black

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3.1.2 Power
The ISA500 is polarity protected and fused with a 400mA resettable poly fuse. Internal
circuitry isolates the supply from the outside environment requiring the serial interface,
TTL trigger and analogue output to use the digital and analogue 0V reference pin.
3.1.3 Serial Interface
The RS232 and RS485 interface is isolated from the supply and has in-line fused
protection on the serial lines. A prolonged transient voltage on these lines will blow the
surface mount fuses which will require replacement by Impact Subsea or an approved
distributor.
3.1.4 RS232 Wiring
Note: RS232 will not function if the digital 0V pin is not use as the
RS232 ground.

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3.1.5 RS485 Wiring
The RS485 termination resistor is software selectable.
Note: The digital 0V must be connected on an RS485 interfaces,
otherwise the voltage potential between one of the A+ or B- lines to
ground could reach a damaging level
3.1.6 Analogue Out and TTL Trigger
The Analogue interface can be configured to output voltage or current. It is isolated
from the supply and has in-line fused protection. A prolonged transient voltage on this
line will blow the surface mount fuses which will require replacement by Impact Subsea
or an approved distributor.
The TTL input can be used to
trigger a ping, update the
analogue output and transmit
the user selected serial string.
These events can happen when
the trigger is connected to
digital 0V or disconnected, the
software allows the user to
choose.
Notes: TTL trigger input is referenced to Digital 0V
Analogue out is referenced to Analogue 0V

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3.1.7 Establishing Communications
The default serial settings are RS232, 9600, N81
If the ISA500 is tilted from vertical to upside down 3 times within the first 10 seconds of
power up then it will temporarily configure the serial interface to the default (RS232,
9600, N81) and output an ASCII message displaying the settings.
Note: When the device is powered cycled the serial interface setting will
revert back to the last configuration.
3.1.8 Connector Mating
When mating the cable to the SubConn connector, to maximise the life of the
connector, it is important to observe the following:
–Always apply grease before mating. Molykote 44 Medium grease must be used.
–Disconnect by pulling straight, not at an angle.
–Do not pull on the cable and avoid sharp bends at cable entry.
–Do not over-tighten the bulkhead nut.
Do not expose the connector to extended periods of heat or direct sunlight. If a
connector becomes very dry, it should be soaked in fresh water before use
3.1.9 Connector Cleaning
General cleaning and removal of any accumulated sand or mud on a connector should
be performed using spray based cleaner (for example Isopropyl Alcohol).
New grease must be applied again prior to mating.

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3.2 Location
When evaluating the installation location of the ISA500, there are several factors to consider to
achieve optimum operation:
–Acoustics (Altitude Measurement)
–Magnetic Disturbers (Heading)
–Alignment with Vehicle (Pitch/Roll)
–Heat Sources (Temperature Measurement)
3.2.1 Acoustics (Altitude Measurement Performance)
The transducer must have a clear view of the seabed. Any items which obstruct this
view may result in erroneous Altitude measurements. If entirely obstructed, no Altitude
readings will be possible.
Ideally the ISA500 should not be operated in close proximity to other acoustic
equipment with the same operational frequency (500kHz). Other acoustic equipment
may cause the ISA500 to produce erratic Altitude readings.
If the ISA500 is found to be causing interference with other acoustic systems, the
operational frequency can be adjusted to move it out of band with the other equipment
– see the seaView application demonstration on our website for details or click into the
ISA500 settings in seaView to see the various settings which can be adjusted.
3.2.2 Magnetic Disturbers (Heading Performance)
Where the heading output is to be used, the ISA500 should be mounted as far as
possible from sources of magnetic interference.
Electrical items which can cause magnetic interference include motors, transformers
and valve packs. Ferrous metals, or any other magnetically active materials will also
have influence on the heading reading. Thus, where possible, the unit should be
installed as far as possible from magnetically active materials.

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3.2.3 Alignment with Vehicle (Pitch/Roll Accuracy)
When mounting vertically, the ISA500 should be mounted with the transducer facing
downwards (to the seabed) and the indentation in the connector end cap pointing
forwards, in the direction of forward vehicle travel:
When mounting horizontally (for horizontal range measurements) the ISA500 should be
mounted with the transducer facing in the direction of measurement to be made, with
the indentation in the connector end cap pointing upwards:
3.2.4 Heat Sources (Temperature Accuracy)
In order for the ISA500 to read the ambient temperature of the water, it should not be
installed in close proximity of any heat sources (such as Hydraulic Power Packs).

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3.3 Mounting
The ISA500 should be mounted using clamps around the mid-section of the body. The forward
looking unit has a 55mm recess in the main body to enable a clamp to be tightened securely
around the unit. The right angled unit has a 46mm recess.
Ideally a non-metallic clamp should be used, however in the event that this is not possible,
effort should be made to electrically isolate the clamp from the ISA500 housing. This can be
achieved by using rubber or plastic strips around the body of the ISA500.
The ISA500 has two flats, on either side of the body – these are to enable the unit to sit tightly
against another flat surface if available. These flats also help prevent the unit moving when on
the workbench for testing.

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4.0 Operation
4.1 Use with seaView software
The ISA500 is supplied with the highly intuitive Impact Subsea seaView software on USB. The
latest version of seaView can be downloaded from www.impactsubsea.com.
seaView is designed to operate all of the Impact Subsea sensors. Single sensors can be
operated, or multiple sensors together.
seaView is designed for use with a PC running the Windows 7, 8 or 10 operating system and
require Microsoft's .net framework 4.5.2 or above
seaView uses an advance framed binary protocol to communicate to the ISA500 and can do so
over RS232 or RS485 at any standard baud rates above 4800. The parity must be none, stop bits
1 and data bits 8. If the ISA500 communication settings differ from this then perform the
communications reset as described in the establishing communications section of this manual.
All settings and offsets are saved to the ISA500 device flash memory.
Impact Subsea Software

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4.2 Integration with Systems
Conceptually there are two modes of operation, Interrogated and autonomous.
Integration mode requires a master to request the ISA500 to make a measurement
and report this back.
The ISA500 can be interrogated by the user defined interrogation string, or by the TTL
trigger input. Upon interrogation the ISA500 will make a measurement and report back
the result over the configured output, whether this be a serial string or analogue voltage
/ current loop output.
Autonomous mode will make a measurement and output the result over serial or
analogue at a specified time interval.
The ISA500 can be configured to operate in one or both of these modes at the same time.
ISA500's with the HMRU option make use of the same interrogated and autonomous
mechanises to output heading pitch and roll data over the serial interface.
4.3 Understanding advanced features
Some serial output strings for altitude measurement report back the energy level of the echo
and a correlation factor.
The energy level ranges from 0 to 1 where 1 represents full saturation of the ISA500 receiver. An
energy level of 0.707 (square root of 2) is the theoretical perfect level as it represents the
energy of a pure sine wave with an amplitude utilising the maximum dynamic range of the
ISA500.
The correlation factor ranges from 0 to 1 which represents a quality factor of the returned
echo. A value of 1 would represent a return echo of perfection with negligible noise and
distortion.
The correlation value can be used alone as a trust factor where low values such as 0.3 mean
there a good possibility it's a false reading. A more detailed picture can be built by combining
this information with the energy level as shown in the table:
Low energy levels
High energy levels
Low correlation
Weak signal probably false
reading
High noise level most
likely a false reading
High correlation
Weak signal but likely a good
reading
Ideal conditions very
trust worthy readings

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These values can also give some insight for adjusting the transmit power. If the energy level is
low then consider increasing the amplitude and length of the transmit pulse.
The ISA500 does not average or filter readings in any way. This provides zero lag making it ideal
for control systems.
A simple reliable target tracking algorithm can be created by applying the last known altitude
reading to analyse the multi echo outputs. Using the correlation and energy values will further
improve the reliability.

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5.0 Servicing
The ISA500 is a highly robust Altitude and Attitude measurement device. The unit has been
designed to require minimal maintenance, and as such there are no user serviceable
components within the unit.
The unit should be rinsed in fresh water to remove growth and salt deposits. If required a light
detergent (such as that used to clean household dishes) can be used.
DO NOT USE SOLVENTS TO CLEAN THE UNIT
Following rinsing the unit should be dried with a cloth.
The connector should be cleaned, and a light coating of Molykote 44 Medium grease should be
applied.
The unit should be stored in its original case, in a cool, dry place.
It is recommended that the unit be returned to Impact Subsea Ltd, on an annual basis to have
a health check and service conducted.

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6.0 Output Strings
6.1 Altitude
ID1: Impact Subsea altitude and temperature
String format:
$ISADS,ddd.ddd,M,tt.t,C*xx<CR><LF>
ddd.ddd = distance in meters from the transducer face to the target.
tt.t = temperature in Celsius
xx = NEMA standard checksum
ID2: Impact Subsea altitude, signal level, correlation and temperature
String format:
$ISADI,ddd.ddd,M,e.eeee,c.cccc,tt.t,C*xx<CR><LF>
ddd.ddd = distance in meters from the transducer face to the target.
e.eeee = energy level (0 to 1)
c.cccc = correlation factor (0 to 1)
tt.t = temperature in Celsius
xx = NEMA standard checksum
ID3: Impact Subsea mutli echo output
String format:
$ISAMD,tt.t,C,ddd.ddd,...*xx<CR><LF>
tt.t = temperature in Celsius
ddd.ddd = distance in meters from the transducer face to the target.
… = another ddd.ddd reading.
xx = NEMA standard checksum
Example string format for 3 echoes (Note: 10 echoes maximum number of multi- echoes
that can be detected):
$ISAMD,tt.t,C,ddd.ddd,ddd.ddd,ddd.ddd*xx<CR><LF>

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ID4: Impact Subsea mutli echo output with signal level, correlation and temperature
String format:
$ISAMI,tt.t,C,ddd.ddd,e.eeee,c.cccc,...,...,...*xx<CR><LF>
tt.t = temperature in Celsius
ddd.ddd = distance in meters from the transducer face to the target.
e.eeee = energy level (0 to 1)
c.cccc = correlation factor (0 to 1)
,...,...,... = another ddd.ddd,e.eeee,c.cccc reading
xx = NEMA standard checksum
Example string format for 2 echoes
$ISAMD,tt.t,C,ddd.ddd,e.eeee,c.cccc,ddd.ddd,e.eeee,c.cccc*xx<CR><LF>
ID5: Tritech 3P3
String format:
ddd.dddm<CR><LF>
ddd.ddd = distance in meters from the transducer face to the target.
ID6: Tritech 2P3
String format:
dd.dddm<CR><LF>
dd.ddd = distance in meters from the transducer face to the target.
ID7: Tritech 3P2
String format:
ddd.ddm<CR><LF>
ddd.dd = distance in meters from the transducer face to the target.

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ID8: Tritech multidrop
String format:
xddd.dddm<CR><LF>
x = node address. This the the first character of the interrogation string.
ddd.ddd = distance in meters from the transducer face to the target.
ID9: Benthos
String format:
Rdd.dd<CR><LF> or when there's no echo return Rdd.ddE<CR><LF>
dd.dd = distance in meters from the transducer face to the target.
ID10: Valeport
String format:
$PRVAT,dd.ddd,M,0000.000dBar*xx<CR><LF>
dd.dd = distance in meters from the transducer face to the target.
xx = NEMA standard checksum
ID11: SDDBT
String format:
$SDDBT,,f,ddd.dddd,M,,F*xx<CR><LF>
ddd.dddd = distance in meters from the transducer face to the target.
xx = NEMA standard checksum
ID12: Tritech bathy mode