SBE 37 MicroCAT CT (P) (DO) Recorder
SUMMARY
SeaBird manufactures a number of instruments within our MicroCAT CTD family, which make measurements at userprogrammable intervals. All MicroCATs:
 Measure Conductivity and Temperature.
 Can include an optional straingauge Pressure sensor.
 Can include an integrated pump (P in the model number designation) for improved biofouling protection and improved conductivity and oxygen sensor response.
 Have 8 Megabyte memory.
 Are available for depths to 350 meters (plastic housing) or 7000 meters (titanium housing).
Some MicroCATs also include Dissolved Oxygen:
 IDO MicroCATs include a membranetype Dissolved Oxygen sensor.
 ODO MicroCATs include an Optical Dissolved Oxygen sensor.
The SBE 37SMPODO MicroCAT can be integrated with a pH sensor to provide CTD + DO + pH:
 SeapHOx^{TM} (37SMPODO with SeaFET^{TM} pH Sensor) is rated to 50 m depth.
 Deep SeapHOx^{TM} (37SMPODO with Deep SeaFET^{TM} pH Sensor) is rated to 2000 m depth.
FEATURES OF EACH MODEL (click link to go to product page)
SeaBird Model Number 
Additional Included Sensors 
Pump*  Power  Communication  RealTime Data 
Minimum Sampling Interval 

Internal  External  
37SMPODO  Optical Dissolved Oxygen (plus pH when integrated with SeaFET^{TM} or Deep SeaFET^{TM}) 
√  √  √  RS232, RS485, or SDI12  √  10 sec 
37SMPIDO (replaced by 37SMPODO) 
Dissolved Oxygen (membrane type) 
√  √  √  RS232 or RS485  √  10 sec 
37SMP  √  √  √  RS232, RS485, or SDI12  √  6 sec  
37SM  √  √  RS232 or RS485  √  6 sec  
37SIPIDO  Dissolved Oxygen (membrane type) 
√  √  RS232  √  1.0 sec  
37SIP  √  √  RS232 or RS485  √  1.0  1.5 sec ***  
37SI  √  RS232 or RS485  √  1.0  1.5 sec ***  
37IMPODO  Optical Dissolved Oxygen  √  √  Inductive Modem ****  √ **  10 sec  
37IMPIDO (replaced by 37IMPODO) 
Dissolved Oxygen (membrane type) 
√  √  Inductive Modem ****  √ **  10 sec  
37IMP  √  √  Inductive Modem ****  √ **  6 sec  
37IM  √  Inductive Modem ****  √ **  6 sec 
* Integral pump provides improved conductivity and dissolved oxygen (if applicable) response, and conductivity fouling protection.
** Inductive Modem MicroCATs do not automatically transmit realtime data; controller must query for data.
*** Minimum sampling interval 1.0 sec without optional pressure sensor, 1.5 sec with optional pressure sensor.
**** See Application Note 92 for a description of Inductive Modem telemetry.
Title  Type  Publication Date  PDF File 

SBE 37 MicroCAT Feature Comparisons  Product Brochure  Wednesday, July 29, 2015  MicrocatFeatureComparisonsJuly15.pdf 
SBE 37 MicroCAT Change Notice  Technical Note  Wednesday, June 6, 2018  TechnoteMicroCATConsolidationNotice.pdf 
How accurate is salinity measured by my CTD? What factors impact accuracy?
One of the reasons that this is not a simple question is that there are several factors to take into consideration regarding the error margin for practical salinity measurements. Salinity itself is a derived measurement from temperature, conductivity, and pressure, so any errors in these sensors can propagate to salinity. For example, our initial accuracy specification for the SBE 3plus temperature sensor and SBE 4 conductivity sensor on an SBE 9plus CTD is approximately equivalent to an initial salinity accuracy of 0.003 PSU (note that conductivity units of mS/cm are roughly equivalent in terms of magnitude to PSU).
However, another issue to consider is that this accuracy is defined for a clean, wellmixed calibration bath. In the ocean, some of the biggest factors that impact salinity accuracy are 1) sensor drift from biofouling or surface oils for conductivity in particular and 2) dynamic errors that can occur on moving platforms, particularly when conditions are rapidly changing, which will be true for all sensors that measure salinity. SeaBird provides recommendations, design features such as a pumped flow path, and data processing routines to align and improve data for the salinity calculation to account for thermal transients and hysteresis, and to match sensor response times. Depending on the environment and the steepness of the gradient, and after careful data processing, this may continue to have an impact on salinity on the order of 0.002 PSU or more, for example. For more details, see Application Note 82.
Lastly, note that salinity in PSU is calculated according to the Practical Salinity Scale (PSS78), which is defined as valid for salinity ranges from 2 – 42 PSU.
Compare Moored / Time Series Recording Instruments
SBE  Measures (C, T, P) 
Auxiliary Sensors  Memory  Power  Communication  RealTime Data 
Comments  
Internal  External  
SBE 16plus V2 SeaCAT CT (P) Recorder  C, T, P*  6 A/D; 1 RS232  64 Mb  RS232  Optional pump  
SBE 16plus SeaCAT CT (P) Recorder 
C, T, P*  4 A/D; optional RS232 or PAR  8 Mb  RS232 or 485  Replaced by SBE 16plus V2 in 2008  
SBE 16 SeaCAT CT (P) Recorder 
C, T, P*  4 A/D  1 Mb  RS232  Replaced by SBE 16plus in 2001  
SBE 16plusIM V2 SeaCAT CT (P) Recorder  C, T, P*  6 A/D; 1 RS232  64 Mb  Inductive Modem  Optional pump  
SBE 16plusIM SeaCAT CT (P) Recorder 
C, T, P*  4 A/D; optional RS232 or PAR  8 Mb  Inductive Modem  Replaced by SBE 16plusIM V2 in 2008  
SBE 19plus V2 SeaCAT Profiler CTD  C, T, P  6 A/D; 1 RS232 
64 Mb  RS232  Programmable mode — profiling or moored  
SBE 19plus SeaCAT Profiler CTD 
C, T, P  4 A/D; optional PAR  8 Mb  RS232  Replaced by SBE 19plus V2 in 2008  
SBE 19 SeaCAT Profiler CTD 
C, T, P  4 A/D  1  8 Mb  RS232  Replaced by SBE 19plus in 2001  
SBE 37SM MicroCAT CT (P) Recorder  C, T, P*  8 Mb  RS232 or 485  
SBE 37SMP MicroCAT CT (P) Recorder  C, T, P*  8 Mb  RS232, RS485, or SDI12  Integral pump  
SBE 37SMPIDO MicroCAT CTDO (P) Recorder  C, T, P*  Integrated DO  8 Mb  RS232 or 485  Integral pump; Replaced by SBE 37SMPODO in 2014  
SBE 37SMPODO MicroCAT CTDO (P) Recorder  C, T, P*  Integrated Optical DO  8 Mb  RS232, RS485, or SDI12  Integral pump  
HydroCAT CT(DO)(P) Recorder  C, T, P*  Integrated Optical DO*  8 Mb  RS232 & SDI12  Integral pump; for Coastal applications to 350 m  
HydroCATEP CTpH(DO)(P)(Chl)(NTU) Recorder 
C, T, P*  Integrated pH, Optical DO*, Chlorophyll*, Turbidity*  16 Mb  RS232 & SDI12  Integral pump; for Coastal applications to 350 m  
SeapHOx Ocean CTDOpH (P) Recorder  C, T, P*  Integrated Optical DO, pH  8 Mb  RS232  37SMPODO with SeaFET pH sensor; to 50 m  
Deep SeapHOx Ocean CTDOpH (P) Recorder  C, T, P*  Integrated Optical DO, pH  8 Mb  RS232  37SMPODO with Deep SeaFET pH sensor; to 2000 m  
SBE 37IM MicroCAT CT (P) Recorder  C, T, P*  8 Mb  Inductive modem  
SBE 37IMP MicroCAT CT (P) Recorder  C, T, P*  8 Mb  Inductive modem  Integral pump  
SBE 37IMPIDO MicroCAT CTDO (P) Recorder  C, T, P*  Integrated DO  8 Mb  Inductive modem  Integral pump; Replaced by SBE 37IMPODO in 2014  
SBE 37IMPODO MicroCAT CTDO (P) Recorder  C, T, P*  Integrated Optical DO  8 Mb  Inductive modem  Integral pump  
SBE 37SI MicroCAT CT (P) Recorder  C, T, P*  8 Mb  RS232 or 485  
SBE 37SIP MicroCAT CT (P) Recorder  C, T, P*  8 Mb  RS232 or 485  Integral pump  
C, T, P*  Integrated DO  8 Mb  RS232 or 485  Integral pump  
SBE 39plus Temperature (P) Recorder  T, P*  64 Mb  Optional  USB & RS232  Optional  
SBE 39 Temperature (P) Recorder 
T, P*  32 Mb  Optional  RS232  Optional  Replaced by SBE 39plus in 2014  
SBE 39plusIM Temperature (P) Recorder  T, P*  64 Mb  Inductive Modem & USB  
SBE 39IM Temperature (P) Recorder  T, P*  32 Mb  Inductive modem  Replaced by SBE 39plusIM in 2016  
SBE 56 Temperature Logger  T  64 Mb  USB  
SBE 26plus Seagauge Wave & Tide Recorder  T, P  C optional  32 Mb  RS232  (tides, waves, & wave statistics) 
Wave & tide recorder  
SBE 26 Seagauge Wave & Tide Recorder 
T, P  C optional  8 Mb  RS232  Replaced by SBE 26plus in 2004  
SBE 53 BPR Bottom Pressure Recorder  T, P  C optional  32 Mb  RS232  Bottom pressure recorder  
SBE 54 Tsunameter Tsunami Pressure Sensor  T, P  128 Mb  Optional  RS232  Tsunami pressure sensor  
C = conductivity, T = temperature, P = pressure, DO = dissolved oxygen 
Compare Inductive Modem Instruments
SBE  Measures (C, T, P) 
Auxiliary Sensors  Memory  Power  Comments  
Internal  External  
SBE 16plusIM V2 SeaCAT CT (P) Recorder  C, T, P*  6 A/D; 1 RS232  64 Mb  Optional pump  
SBE 16plusIM SeaCAT CT (P) Recorder 
C, T, P*  4 A/D; optional RS232 or PAR  8 Mb  Replaced by SBE 16plusIM V2 in 2008  
SBE 37IM MicroCAT CT (P) Recorder  C, T, P*  8 Mb  
SBE 37IMP MicroCAT CT (P) Recorder  C, T, P*  8 Mb  Integral pump  
SBE 37IMPIDO MicroCAT CTODO (P) Recorder  C, T, P*  Integrated DO  8 Mb  Integral pump; Replaced by SBE 37IMPODO in 2014  
SBE 37IMPODO MicroCAT CTODO (P) Recorder  C, T, P*  Integrated Optical DO  8 Mb  Integral pump  
SBE 39plusIM Temperature (P) Recorder  T, P*  64 Mb  Includes internal USB connector for fast data upload  
SBE 39IM Temperature (P) Recorder  T, P*  32 Mb  Replaced by SBE 39plusIM in 2016  
SBE 44 Underwater Inductive Modem (UIM)  1 RS232  30 Kb buffer  Integrates sensor with standard serial interface (current meter, Doppler profiler, etc.) to inductive modem telemetry system  
Underwater Inductive Modem Module (UIMM)  1 RS232  16 Kb Sample Data Memory  Integrates sensor with standard serial interface (current meter, Doppler profiler, etc.) to inductive modem telemetry system; more flexible and economical than SBE 44  
C = conductivity, T = temperature, P = pressure, DO = dissolved oxygen Notes: 