SBE 8 Microstructure Temperature Sensor
The SBE 8 Microstructure Temperature Sensor is a reliable, lightweight instrument intended for use in marine profiling applications where its high speed and spatial resolving power offer the ability to characterize small-scale ocean temperature features. Used in conjunction with the SBE 7 Microstructure Conductivity Sensor, the SBE 8 can provide comparably sensitive resolution of salinity and density fields.
Although the SBE 8 is intended primarily for determination of temperature gradients, it is configured to respond also to absolute temperatures:
- The gradient sensitivity of the sensor is a function of its average zero-frequency response and may be evaluated by integrating that response.
- The functionality of the instrument is verified by its proper static response.
- It is accurate enough as an absolute sensor (typically within 0.01 °C for periods of several hours at atmospheric pressure) to provide absolute temperature data.
- Sensing element is a remote-cabled, probe-mounted thermistor (Thermometrics type FP07).
- Sensor probe is a small, stainless steel assembly that may be mounted up to 3 m from sensor electronics housing. This arrangement minimizes effect of instrument housing and its wake on the data.
- Thermistor body is O-ring sealed into the sensor assembly to ensure pressure integrity.
- Aluminum housing; depths to 6800 m.
- Five-year limited warranty.
- Cabled remote probe (up to 3 m length) or probe mounted to sensor housing.
- AG or wet-pluggable MCBH connector.
The thermistor has a 25 °C resistance of 270 K ohms and is driven by a DC current derived from a low-noise, 6.9 volt reference and 1 megohm resistor. The thermistor voltage is buffered by a low-noise FET op amp. The output is subsequently pre-emphasized, so the sensor’s output increases as a function of the frequency components in the temperature signal. The effect of pre-emphasis is to magnify the sensor output for rapidly changing temperature, thereby overcoming restrictions on system resolving power that would otherwise be imparted by the use of conventional (e.g., 16-bit) digitizers. The SBE 8’s pre-emphasis response magnifies a 20 Hz temperature signal by a factor of 200, thus facilitating acquisition of signals 200 times smaller than could be characterized by conventional CTD sensors.
General characteristics of similar sensors are described in a paper by Gregg, et al 1. A discussion of field experiences with instruments of this type may be found in another paper by Gregg 2.
1 Gregg, M.C.; T.B. Meagher; A.M. Pederson; and E. Aagaard, “Low Noise Temperature Microstructure Measurements with Thermistors”, Instruments and Methods, Deep-Sea Research, Vol 25, pp 843-856, 1978.
2 Gregg, M.C., “Variations in the Intensity of Small-Scale Mixing in the Main Thermocline”, Journal of Physical Oceanography, Vol 7,
pp 436-454, 1977.
|High-Speed Micro-Scale Resolution||-3 db at 22 Hz (sensor)
-3 db at 1000 Hz (electronics)
|Extremely Low Noise||8 x 10-7 (°C) / (Hz1/2)
Pre-emphasized response to overcome system thresholds
|Temperature Element||High-speed thermistor, Thermometrics type FP07.
Cabled (up to 3m) remote stainless steel probe assembly.
|Input Power||± 15 V ± 3% at 25 mA|
|Voltage, +6 to -6 V for -3 to 30 °C nominal at 0 frequency
Output increases in proportion to frequency, beginning at 0.1 Hz and ending at 200 Hz.
|Housing & Depth Rating||Hard-anodized 7075-T6 aluminum, zinc anode protected,
4.8 cm diameter x 18 cm long,
6800 m depth rating
|Connector||6-pin Impulse AG 306 (1/2-20 thread) or MCBH-6MAL|
|Weight||0.7 kg in air, 0.3 kg in water|
What is the function of the zinc anode on some instruments?
A zinc anode attracts corrosion and prevents aluminum from corroding until all the zinc is eaten up. Sea-Bird uses zinc anodes on an instrument if it has an aluminum housing and/or end cap. Instruments with titanium or plastic housings and end caps (for example, SBE 37 MicroCAT) do not require an anode.
Check the anode(s) periodically to verify that it is securely fastened and has not been eaten away.
|8||MICROSTRUCTURE TEMPERATURE SENSOR - 6800 m depth, with probe. Includes Microfit software & complete documentation.|
|SBE 8 Probe Configuration Selections — MUST SELECT ONE|
|8-1[X]||Cabled remote probe (80015.2x), [X = length] up to 3 m||Remote probe (shown here) minimizes effect of instrument housing and its wake on data.|
|8-2[X]||Probe (80015.4) mounted to sensor housing|
|SBE 8 Wet-Pluggable Connector Option|
|8-3||Wet-pluggable (MCBH) connector instead of XSG connector||
Wet-pluggable connectors may be mated in wet conditions. Their pins do not need to be dried before mating. By design, water on connector pins is forced out as connector is mated. However, they must not be mated or un-mated while submerged. Wet-pluggable connectors have a non-conducting guide pin to assist pin alignment & require less force to mate, making them easier to mate reliably under dark or cold conditions, compared to XSG/AG connectors. Like XSG/AG connectors, wet-pluggables need proper lubrication & require care during use to avoid trapping water in sockets.