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HRPH Sensors for May 2009 Deployment
HRpH Sensors for May 2010 Deployment
HRpH Sensors for Apr 2011 Deployment
HRPH Tech Transfer Package For Heron Island - tech transfer package was prepared but not used, UQ Heron Island decided to have Nido Instruments do the build instead

HRPH Project Background 

Ocean Acidification Instruments / Studies such as FOCE require a precision pH sensor capable of operating up to full ocean depth (4000m).

The Seabird SBE 18-I is presently used.    The pH sensor problems found on FOCE and BRS after talking with Ed Peltzer, Bob Herlein and Craig Okuda.

1. The housing leaks.
2. The sensor rails possibly due to physical placement near motors and either does not recover or takes 20 to 30 minutes to recover.
3. Seawater diffuses into the KCL electrolyte resulting in an offset over time.    The pH sensor also exhibits slow response when the reference KCL has been infiltrated with seawater.

Notes from Thom on possible solutions:

1. Improve the housing design.   Also look at documenting a procedure to seal and test the existing housing reliably.
2. Redesign the sensor electronics and improve the grounding and isolation.    Provide an isolated digitized output.
3. (Possible Innovative idea) Use 'standardized' Seawater as the electrolyte to mitigate affects of prolonged exposure to seawater.    Preliminary reading about the chemistry of the sensor and a brief discussion with Ed Peltzer last wee (7/31) seemed to indicate this approach might work.
   

Notes on FOCE system issues found during pH testing

1. Mink-10 connector on FOCE can is not straight thru wired to DJ's Mars simulator can 
2. Motor back EMF problem due to 24v motor being operated at 24v.   EMF problem is there at 2000 rpm and very pronounced at 3000 rpm.  The result is current slewing 4A to 8A at 3000 rpm.  Manufacturer recommends operating at 48v however the EZ servo upper limit is 42v.
3. There is a blown channel (#3) on the A/D card in the PC104 stack.   The reading is always 4.999v.
4. Loose connectors to the A/D card in the PC104 stack.   Wiggling this connector causes the pH readings to rail.
5. Hardisk cable rubbing on a sharp edge caused a hard disk failure
6. Ethernet connection is sometimes flaky
7. Loose power connection to PC104 relay board - screw terminals need tightening
8. FOCE pressure housing is tied to Ground through the metal chassis 
9. 24v Fuse is 8A, should be at least 10 to 12 slo blow.
10. FOCE vibrates noticably when operated just below the surface - this vibration may have been interacting with the A/D connector.
    

Modifications to address FOCE system issues

1. No modification for Mink-10 connector as the ODI connector defines the MARS interface.  Team educated to always use the test cable.   Note: as a lessons learned, perhaps the use case of bench testing should be a requirement and the Mink-10 connector pinouts should be the same to enable use of a straight thru cable.
2. 36v power supply added to drive the motor and give headroom for operation at 2000 rpm (max spec'd speed)
3. Replaced A/D card fixed the blown channel #3 problem
4. Replaced the pins in the connector for a more positive contact
5. Replaced harddisk mounting bracket and removed sharp edges.   Also re-routed harddisk cable away from the Ethernet.
6. Replaced ethernet connector with a factory connector from Lippert.
7. Tightened screw terminals.
8. Removed chassis from pressure housing lid - used mylar to insulate chassis from pressure housing lid.
9. FUSE replaced with 10A.
10.  

Design of sensor electronics with improved grounding and isolation

1. Requirements
   1. Meet or exceed Seabird18 for accuracy and performance without being susceptible to railing or errors when operated with the full range of the FOCE motors.
   2. Match electrical spec of Seabird 18 as used by FOCE
      1. Power: 6-24v dc, 7mA. (Measured at 14mA)
      2. Analog signal output:  0 to +5v
2. Isolation - isolate analog front end from connection to FOCE (break the ground loop)
   1. Option A: is to use an isolated power supply and an analog isolator
   2. Option B: isolated power supply, A/D converter, microprocessor for signal processing / correction,  digitized ph sent RS232 or RS485
   3. Option C: same as option B, but convert pH back to analog.   This option will be used for the engineering test if we don't have the resource to write a SIAM serial driver.  
3. Best in class analog front end -
   1. pH probes are typically 40M to 400M ohms impedance and a proper front end should present 10x or more of that impedance to properly read the sensor.
   2. Key factors in opamp selection are:
      1. super high input impedance
      2. super low bias current
      3. offset voltage drift / temperature stability
      4. availability
      5. power consumption
   3. Seabird18 uses a single AD549 op amp, BRS team uses LM6001.  
      1. INA116 is an instrumentation amp with 3 fA bias and 0.1 Peta ohm input impedance (10 to the 14 - yikes)
      2. AD549 
      3. AD648
      4.  
4. Improve analog front end grounding
   1. Several articles on high resolution pH show grounding the analog front end to the solution being measured
      

Hardware Design

Analog Front End Board

1. pH probe interface with ultra low bias Instrumentation amplifier used (INA116)
2. no filter capacitors in the high impedance signal chain to improve recovery times.
3. Next rev
   1. add linear regulators for power filtering to the front end board.
      

pH Meter Board

1. MSP430F2618 / 169 chosen for software reuse from Valve Pack Controller project
2. ADS1251 24bit converter (19 ENOB) chosen for it's precision and software simplicity plus the 4th order 50/60 Hz notch filter and low power consumption
3. ADM1411 digital isolator chosen for the microprocessor to A/D converter interface.   Also provides 3.3v to 5.0v level shift
4. 12v input, isolated dual output (+/- 15v) DC/DC converter - VInfinity chosen for it's lower noise figure.
5. LM337 / LM317 chose for adjustable linear regulators for the sensitive analog section
6. MAX3222 for RS232 interface
7. MAX3483 for RS485
8. MSP430F169 12-bit D/A converter chosen for analog output (temporary) option.    With over-sampling and proper filtering it is believed we can get 15 to 16 bit accuracy.   2nd order Sallen-Key filter designed for approx. 50 Hz cutoff frequency.
   1. http://sim.okawa-denshi.jp/en/OPstool.php  filter calculator was used and standard resistor (39K) and cap parts (0.1uf) selected.
   2. Cutoff Freq: 57.7 Hz   R1=39K, R2=39K, C1=0.1uF, C2=0.05uF
   3. Q = 0.707
9. 29M2f08  Micron NAND flash
10. AD8609 Quad OpAmp for bipolor to unipolar translation, Reference buffering, Analog output and DAC filtering, and 2 channel vibration sensor input
11. AD680 2.5000v Reference
12.  

Assembly Notes

1. Controller Board   
   1. Conformal coating
   2. JTAG connector
   3. Front End board connector
2. Front End Board
   1. pH electrode attachement
3. Pressure Housing Assembly
   1. Board mounting
   2. 3 wire connection
      1. White = Ground
      2. Green = +12v
      3. Black = pH Analog out or TX data Digital out
   3. Testing
   4. 55 O-Ring grease
   5. Aqua Lube
4. Testing
   

Note:  the DGH can (see Dale Graves for info) converts the pH sensor from analog to digital and sends the digital by serial bit stream (RS232 or RS485).

Oct. 3rd Test

Pin 1 - white - GND

Pin 2 - black - pH

Pin 3 - green - +12v

With 12.0v applied, the Seabird pH instrument pulls 12mA (as indicated by the Tenma power supply)

HRPH For FOCE

1. 2 Development boards, 6 deployment boards
2. Serial protocol definition / implementation / test
   1. Request / Response protocol
   2. Sampling configurability 
   3. study DGH protocol, decide between DGH and proprietary
   4. implement test harness (C program)
   5. implement and test the protocol
   6. document the protocol
3. Finish Flash data logging driver
   1. circular
   2. upload
   3. erase (clear)
4. 6 conductor, 4 Wire connector modification for the digital interface
   1. RS232 (RX,TX), GND, +12v
5. Build Test and Qualify 6 new probes
   1. Housing selection from Peter Walz and Ed Peltzer
   2. New o-rings
   3. Pressure test (Nalgene bottle or attaced to the ROV during a dive)
6. Calibration
   1. Modify the Calibration software if needed.
   2. Run Ed's calibratinion routine

FOCE - Deep Ocean Wireless Power and Data Transfer (Discussed with Bill Kirkwood / Mike Risi)

1. Inductive Power Transmitter and Receiver (2W for HRpH, 10W to cover other instruments like CTD)
2. 38400 Baud serial data comms (RF or Optical)
3. 6 conductor, 5 wire connector pinout 
4. Software
   1. PUCK enabled
5. Packaging and Mechanical
   
   

Protocol Definition

The DGH D5000 series products use a simple command and response protocol. A module must be interrogated by a host computer to obtain data. A module will never initiate a command sequence in order to prevent communications collisions.
A command is initiated with a command prompt, may be a dollar sign ($) or pound sign (#). Following the prompt a single address character must be transmitted. Each module on a communications bus must be setup with a unique address. The address is followed by a two character command. Every command is terminated with a carriage return.
The module response begins with a response prompt, which is an asterisk followed by the necessary data. Every response is terminated with a carriage return. Linefeeds after the carriage return are user selectable. See the table below for typical commands and their respective response messages.