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HEAT FLOW PROBE SYSTEM SPECIFICATIONS

ELECTRONICS:

i) Power capacity and solid-state (no moving parts) logging of all data over a period of up to 24-hours.

ii) Tilt, pressure, and water-temperature measurements in addition to eleven sediment-temperature measurements.

iii) An acoustic data link capable of reliably transmitting data from depths to 5000 meters.

MECHANICAL DESIGN OF ELECTRONICS:

i) All electronics and batteries fit into a single, cylindrical pressure case. Nominal interior space is 6" dia. x 26" long.

ii) Modular construction of electronic functions should facilitate future upgrades and modifications, in particular to access the penetration (pressure) sensor, and possibly to expand the data logger and A/D functions.

OPERATIONAL REQUIREMENTS:

i) All normal daily operations, including communications, data retrieval, and battery charging can be accomplished without opening any of the pressure cases (i.e., via external underwater connectors).

ii) Electronics can function without adjustment over the temperature range; -5oC to +30oC.

iii) For test and normal operational purposes, some probe functions can be driven by software commands.

THERMISTORS:

i) Thermistors used for temperature measurement are YSI44032.

ii) Current through each thermistor during the measurement period is minimized to keep self-heating errors small.

iii) Thirteen temperature-equivalent channels are sampled. Eleven thermistors are in the probe itself, an additional separate thermistor for water temperature measurements is mounted on top of the instrument housing, and a fixed resistor is used as a reference "thermistor".

iv) Each thermistor is individually connected to the electronics, reducing the chances of interference and mechanically induced failure of the sensor string.

THERMISTOR INTERFACE:

i) A minimum differential temperature resolution of +/- 1 moC, with +/-0.7 moC resolution typical, is available over a measuring temperature span of -5oC to +50oC.

ii) Values recorded are inversely proportional to the thermistor resistance. Resistance to temperature conversion is done external to the data logging operation, allowing individual resistance-to-temperature conversion parameters to be used for each thermistor if desired.

PRESSURE:

i) Pressure measurements over the depth range of 0 to 6000 meters are made, with better than 1 cm resolution of pressure change. Data storage of 24 bit words provide this resolution.

ii) A Paroscientific transducer Series 8B 7000-2 is used. The gauge is mounted in the instrument weight stand outside the pressure case.

iii) Only electrical wires from the pressure sensor penetrate the pressure case. Hydraulic tubing carrying external pressure is not brought into the interior of the pressure case.

TILT

i) Tilt measurements are made over the range 0o to 40o (from vertical) with a resolution of approximately 0.5o.

ii) The tilt transducer is located inside the pressure case.

TIME:

i) Real time (day/hour/min/sec) is recorded with the data. Time is accurate to within +/- 1 sec over 24 hours.

ii) Time is settable and checkable from outside the pressure case via an RS-232 data link.

iii) The real time clock is powered from an independent power source.

A/D CONVERSION AND SAMPLE RATE:

i) Sixteen-bit A/D converters are used in the electronics.

ii) Fastest scan rate (for 16 data channels - 11 thermistors, reference, water temperature thermistor, pressure, tilt, and time) is 1 scan/10 seconds. Scan rate is programmable (via an external RS-232 link) to include 1 scan per 10 to 60 seconds.

iii) All 16 data channels (11 probe thermistors, reference, water temperature thermistor, pressure, tilt, and time) are sampled within 1 second. In this manner, the time difference between sample times for each thermistor need not be taken into account.

CONTROLLER:

i) The controller is a 16-bit microprocessor chosen to allow flexibility and ease of modification.

ii) The operating program and normal default start-up configuration (number of channels, scan rate, etc.) is stored in ROM so that the system can be turned on and used immediately. Capability to change the configuration and issue operational commands is provided via a standard communications program. Access is gained through an RS-232 link at 9600 baud.

DATA STORAGE:

i) Data are stored in RAM. An on-board battery provides back-up should there be a failure of the main battery system. Old data are retained after data retrieval, and are overwritten only after an explicit command requiring verification.

ii) There is sufficient memory to store 24 hours of continuous data when scanning 16 channels (11 thermistors, reference resistor, water temp, pressure, tilt, and time) once every 10 seconds.

iii) Data storage ceases when memory is full.

DATA RETRIEVAL:

i) Data are retrieved via an external asynchronous 3-wire RS-232 connection at 9600 baud. Other speeds can be set.

HEAT PULSE CIRCUITRY:

i) Initiation of Heat Pulse: The heat pulse begins only after the probe has penetrated the sediments and has remained stationary for a time interval of approximately 7 minutes. This time interval is programmable (before deployment) in 1 minute increments between 5 and 15 minutes. This time interval allows the temperatures measured after penetration to approach equilibrium (to measure thermal gradient), and also allows pull-out of the probe before a heat pulse (application of the heat pulse for conductivity determination may not be required for all penetrations). Provision is also made for the test-firing of a heat pulse on deck with a user command.

ii) Detection of penetration and stationary period: A constant pressure, within +/- a programmable threshold (nominally 1 meter, programmable from 10 cm to 10 m), as indicated by the pressure sensor (see Section 6.0), is utilized to indicate a stationary penetration condition. Changes of more than the threshold restart the time interval period of Section 13.1. Once one heat pulse has been completed, further heat pulses are inhibited until the pressure sensor has indicated a pressure change of nominally +/-10 meters (i.e. after the probe has been withdrawn from the sediments; programmable from +/-1 to +/-10 meters). Heat pulses are also inhibited while the sensed depth is less than 30 meters (programmable), to prevent heat pulses from occurring while preparing the probe for deployment.

iii) Power to the heater wire: Current is applied for a programmable length of time (typically 20 seconds) beginning only after the probe has remained stationary for the desired interval (see Sec. 13.1). The length of the heat pulse is programmable in 1-second increments over the range 5 to 40 seconds.

iv) The time of application of the power to the heater wire is fixed in relation to the data scan cycle.

v) The total power-time product delivered to the probe heater wire during a "heat pulse" is known, repeatable, and stable, with a target value of 600 joules/(meter of probe length).

vi) Current is regulated at a level that is operator selectable in less than 1 A steps from about 1 to over 10 A. If the current falls below the regulated value, software and acoustic flags are set, alerting the operator to the condition.

vii) Total Number of Heat Pulses: The minimum number of available, properly regulated heat pulses per deployment is dependent on the state of charge of the batteries, and is typically 20.

ACOUSTIC TELEMETRY TRANSMISSION:

i) Type and Amount of Data Transmitted: As previously mentioned, reliability of a limited amount of data is more important than larger amounts of unreliable data. For this reason, a simple delayed-ping scheme has been implemented, with additional consideration given to future provision of a real-time ASCII-coded data for full-data transmission at a later date. The delayed-ping scheme works in the following manner: Only up to 5 channels of information (programmable, but typically tilt and temperature information from 3 thermistors) are transmitted. Each channel is allocated a 1-second information window. At the beginning of each second, a reference ping (5-ms pulse at 12 Khz) is transmitted, followed by a second ping where the time delay (0 to 1 sec) is proportional to the channel data value. For temperature, the conversion is nominally 10oC per second (i.e. there will be N-1 folds for a 10xN oC temperature span). This conversion is selectable from 1 to 10oC per second. For tilt the conversion is nominally 40o per second (i.e. no folding required for full-scale tilt).

ii) Telemetry Output: A simple contact closure of approximately 5 ms duration triggers a separate pinger having its own pressure case and power supply.

iii) Interference to Data Logging: Telemetry transmission does not interfere with, or induce errors in, the logged data. To ensure this, transmission and data acquisition do not occur simultaneously.

BATTERIES:

i) Sealed lead-acid batteries are utilized in the heat probe.

ii) Batteries can be charged via an external connector at the end of each 24-hour operation period without opening the pressure case.

iii) Battery chargers are supplied.

DOCUMENTATION:

i) Full documentation will be supplied for the operation and maintenance of the electronics, for operation of the system at sea.

ii) Programs to convert the raw data files downloaded from memory to a simple ASCII data file, and to view and subdivide data files are provided.

iii) Construction drawings are supplied for the mechanical assembly.

CALIBRATION AND INTEGRATION WITH MECHANICAL COMPONENTS:

i) The electronics are fully integrated into the pressure case, wired into pressure-case bulkhead connectors, and bench-tested with a thermistor string, external pressure sensor, and data-telemetry pinger.

ii) A calibration of the electronics using a high-precision decade resistance unit to simulate the characteristics of the thermistor string are completed and results provided. The result of this, and of the calibration of the tilt sensors are incorporated into the ASCII conversion program.

MECHANICAL CONSTRUCTION:

i) The structural member of the instrument is a 6 cm diameter solid alloy steel bar that extends continuously from the wire termination at the top to the sensor-tube support fin at the bottom.

ii) Driving weight is provided by a 500 kg monolithic weight stand, constructed of galvanized steel and lead fill, that also serves to house and protect the instrument pressure cylinders.

iii) Access to all external connectors on the instrument cylinders is possible without removing the cylinders from the weight stand (i.e., for battery charging and RS-232 communications).

iv) The thermistor sensors and heater wire are contained in a high-strength 10 mm diameter tube supported in tension 10 cm away from the strength member. Two spare sensor tube assemblies are supplied with the instrument.

v) The instrument must be tethered with a 13-mm (nominal diameter) coring wire. A universal swivel termination at the top of the heat probe is supplied. The Ship is required to supply a mating 13 mm yoke swivel wire termination.