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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.


25 cm pathlength 47 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 input 7–15 VDC
Current draw <35 mA (typ); 50 mA (max)
Data output 0-16380 counts (0-5 V)
Output resolution  14 bit
Sample rate to 8 Hx


Rated depth:

600 m (plastic)

6000 m (aluminum)

Temperature error  0.02 percent F.S/deg C
Operating range 0-40 deg C
Long term stability  0.02 percent F.S./ Hr



25 or 10 cm

Wavelengths 470, 530 or 650 nm
Acceptance angle  ~ 1 deg
Bandwidth, 470, 530, 660 nm ~ 20 nm
Bandwidth, 370 nm ~ 10-12 nm
Linearity 99% R2
The list below includes (as applicable) the current product brochure, manual, and quick guide; software manual(s); and application notes.

What should I use to lubricate bulkhead connectors?

We recommend 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.

How do I clean the optical surfaces on my transmissometer?

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. Optional Equipment An adapter cable is available to connect the new 6- pin connector to existing 4-pin cabling. Order part number EXA-210317. The adapter cable connects a 6-pin C-Star to existi ng cabling. Note that if your application requires this adapter, it should be use d as a cable extension. Disconnect ONLY at the 6-socket end, as it is a more robust connector.

What is the input voltage range for my instrument?