Turbidity

Why is silicone oil important in turbidity meter measurements?

Q: Our turbidity meter comes supplied with a bottle of silicone oil. What is this for? Why is it important in the test?

Silicone oil is often supplied with turbidity meters, but what is it used for, and why is it important to the test?
Silicone oil is often supplied with turbidity meters, but what is it used for, and why is it important to the test?

A: The silicone oil is used to ensure the glass vial used in the turbidity meter has a perfectly smooth surface with no interference from scratches on the glass surface.

2100Q turbidity meter
Turbidity meters, like the Hach 2100Q pictured, usually come supplied with Silicone Oil to smooth out any scratches in the test vial

Turbidity meters work by a beam of light shining onto the sample, which is then reflected by suspended particles in the sample. A detector measures the light which is reflected by 90° and this is used to report the turbidity value. Our previous blog post here explains this in more depth.

If the glass sample vial has a scratch on it this will reflect or interfere with the light path, leading to a false result. Remember the scratch may not be visible to the human eye, but could still cause errors.

Putting just 1-2 drops of silicone oil onto a lint free cloth and carefully polishing the vial before placing it into the meter makes sure any scratches are smoothed over, giving a good result.

Some modern meters get around this using different measurement technologies – for example the Hach TU5 series take 1000 readings in a 360° circle around the sample, then average them out. This means if there is a scratch it is corrected for by the averaging, so silicone oil is not needed with these meters. Find out more about this technology in our previous blog post here.

 

To find out more about turbidity meters and other water testing techniques, follow the links above or contact us with your questions;

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