C-Star Transmissometer

The C-Star incorporates a novel monolithic housing with a highly integrated opto-electronic design to provide a low cost, compact solution for underwater measurements of beam transmittance.

The instrument is capable of either free space measurements, or through the use of an optical flow tube, flow-through sampling with a pump. It can be used in profiling, moored, or underway applications. 

WET Labs’ latest generation C-Star Transmissometer offers versatility in applications with high resolution RS-232 data output. The new C-Star maintains its robust mechanical design.
  •  14 bit analog and digital output
  •  Outputs calculated attenuation
  •  ECOView software included
  •  Compatible with previous generations
  •  Optional flow tube
  •  10 and 25 cm pathlengths available
  •  Available in 6000 meter depth rating
  •  Easily interfaced
  •  Available in multiple wavelengths


25 cm pathlength47 x 6.4 x 9.3 cm
10 cm pathlength

29.2 x 6.4 x 9.3 cm

Weight in air

2.2 kg (plastic) 

3.6 kg (aluminum)

Weight in water

0.9 kg (plastic)

2.7 kg (aluminum)


Power input7–15 VDC
Current draw<35 mA (typ); 50 mA (max)
Data output0-16380 counts (0-5 V)
Output resolution 14 bit
Sample rateto 8 Hx


Rated depth:

600 m (plastic)

6000 m (aluminum)

Temperature error 0.02 percent F.S/deg C
Operating range0-40 deg C
Long term stability 0.02 percent F.S./ Hr



25 or 10 cm

Wavelengths470, 530 or 650 nm
Acceptance angle ~ 1 deg
Bandwidth, 470, 530, 660 nm~ 20 nm
Bandwidth, 370 nm~ 10-12 nm
Linearity99% R2
Specifications are subject to change without notice.
Product Brochure

Cstar 10 cm product drawing

Tuesday, February 12, 2013
Product Brochure

Cstar 25 cm product drawing

Tuesday, February 12, 2013
Product Datasheet

C-Star datasheet

Monday, December 5, 2016
Product Manual

Transmissometers User Manual

Wednesday, May 17, 2017
Technical Note

Cable and Bulkhead Connector Maintenance

Thursday, March 9, 2017
Technical Note

Functional check and cleaning of transmissometer windows

Thursday, April 27, 2017
Technical Note

Repairing anodized surfaces

Thursday, April 27, 2017
Technical Note

Instrument Voltage Ranges (in VDC)

Thursday, June 21, 2012
Technical Note

How do I get an adapter cable to connect it to my existing system?

Friday, June 22, 2012

What should I use to lubricate bulkhead connectors?

WET Labs recommends keeping the connectors on your meter lubricated using a good quality silicone spray lubricant, such as 3M Silicone Spray or Loctite 8021 spray. These can be purchased at your local hardware store. Avoid silicone grease. It is messy and attracts contaminants. 

Do not use WD-40. It will destroy connectors.

Do you want WET Labs to review your data?

In order for data questions to be answered in an efficient manner, WET Labs requests:

-  The serial number of the instrument data in question. The most current calibration information
can be verified and the instrument settings upon delivery can be checked.

-  Description of the deployment configuration. Questions to consider:

  •   What are the current instrument settings?
  •   What is the instrument orientation?
  •   Are there possible obstructions?
  •   Is it being used in a mooring, a profiler, or being towed?
  •   What were the deployment date and geographical location?
  •   How far into the deployment was the problem seen?
  •   What power supply and cabling are being used?
  •   What was the instrument condition during the last field service or retrieval?
  •   Do you have any pictures?

-  Raw data files of the physical data in question

  •   examples of good raw data.
  •   examples of questionable raw data .

-  Information about how the raw data was processed.

How do I clean the optical surfaces on my transmissometer?

Functional Checks and Cleaning Methodology for WET Labs Transmissometers Download PDF

My new C-Star has a 6-contact bulkhead connector. How do I get an adapter cable to connect it to my existing system?

The standard bulkhead connector for C-Stars is a 6-pin bulkhead connector. This replaces the 4-socket connector previously used. Download PDF techniacal note.