Digital Reversing Thermometer SBE 35RT
Digital Reversing Thermometer 
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SUMMARY The SBE 35RT is an accurate, ocean-range temperature sensor that is capable of measuring temperature in the ocean to depths of 6800 meters (22,300 ft). The SBE 35RT communicates via a standard RS-232 interface at 300 baud, 8 data bits, no parity. APPLICATIONS The SBE 35RT is used with the SBE 32 Carousel Water Sampler and one of the following CTD systems:
The SBE 35RT makes a temperature measurement each time a bottle fire confirmation is received, and stores the value in EEPROM. Each stored value contains the time and bottle position in addition to the temperature data, allowing comparison of the SBE 35RT record with CTD and water bottle data. Using one SBE 35RT eliminates the need for reversing thermometers, and provides higher accuracy temperature readings at lower cost. Calibration coefficients stored in EEPROM allow the SBE 35RT to transmit data in engineering units. Seaterm, the terminal program in our Seasoft© V2 software suite, provides easy SBE 35RT setup and data uploading. When configured in a real-time system, the SBE 35RT can use the system modem channel for two-way communications; it is not necessary to change cable connections to communicate with and retrieve data from the SBE 35RT. The SBE 35RT can be supplied with an optional, small, desktop Interface Box that is connected to the SBE 35RT and a computer for setup and lab use. The Interface Box is 110/220 VAC powered, provides 15 VDC to the SBE 35RT, and buffers the communication lines to minimize interference from external noise. When used with the Interface Box, user-selectable operating modes are:
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MEASUREMENT METHOD
Temperature is determined by applying an AC excitation to reference resistances and an ultrastable aged thermistor with a drift rate of less than 0.001 °C per year. Each of the resulting outputs is digitized by a 20-bit A/D converter. The reference resistor is a hermetically sealed, temperature-controlled VISHAY. The switches are mercury wetted reed relays with a stable contact resistance. AC excitation and ratiometric comparison using a common processing channel removes measurement errors due to parasitic thermocouples, offset voltages, leakage currents, and gain errors. Maximum power dissipated in the thermistor is 0.5 microwatts, and contributes less than 200 µK of overheat error. The output from the sensor is a raw count related to resistance measurements:
Sensor
Output (raw counts) = 1048576 * (NT - NZ) / (NR - NZ)
where: NR is reference resistor output, NZ is zero ohms output, and NT is thermistor output.
Each measurement acquisition cycles takes 1.1 seconds. The number of cycles per measurement is programmable. Increasing the cycles increases acquisition time while reducing RMS temperature noise from the sensor. In a thermally quiet environment, the temperature noise standard deviation is 82 * sqrt (1/n cycles) [µK].
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SPECIFICATIONS
| Measurement range | -5 to +35 °C |
| Initial accuracy | ± 0.001 °C |
| Typical stability (per year) | 0.001 °C |
| Resolution | 0.000025 °C |
| Sensor calibration | -1.5 to + 32.5 °C |
| Data storage | Up to 179 samples |
| Real-time clock | Watch-crystal type |
| External power | 9 - 16 VDC |
| Current | On power
application (≈ 1 minute):
140 – 160 mA Operating: 60 – 70 mA |
| Housing materials | Aluminum, rated at 6,800 meters (22,300 feet) |
| Weight | In water: 0.3 kg (0.7 lbs) In air: 0.7 kg (1.5 lbs) |
ADDITIONAL INFORMATION / LINKS:
Documentation -- manual, photos, technical papers, application notes, etc.
Sales Information -- options, accessories, cables, mount kits, spares, etc.
Software -- components of Seasoft V2
Links to Other Instruments of Interest
Specifications are subject to change without notice.
Sea-Bird Home Phone: (+1) 425-643-9866 E-mail: seabird@seabird.com
