SCD 355 loosing sensitivity over time

Kake, the reaction cell is pretty easy to clean. The important thing is to make sure the room is dark when you are removing the PMT. I wrap the  capped PMT in a dark labcoat and store it in a drawer, then turn the lights back on to clean the reaction cell, use methanol or DI for cleaning.. You may also need to replace the PMT filter, especially if it is obvious that a lot of ozone corrosion has occured on the filter.  Also be careful with the post-ozone restrictor that is inside the reaction cell, it should not be bent.

If the previous poster is right and you have a post-ozone restrictor problem, you can remove the post ozone restrictor and measure the flow coming out the end of the restrictor. It is supposed to be between 20-30 mL/min. The post-ozone restrictor is a P/N that you can replace.

Lastly when was the last time you replaced your ozone generator? Other than signal issues, you can visually inspect your ozone generator to determine if it has failed (or failure is imminent). The tube inside the generator will change from gray to dark brown/orange as it fails.

Kake, the reaction cell is pretty easy to clean. The important thing is to make sure the room is dark when you are removing the PMT. I wrap the  capped PMT in a dark labcoat and store it in a drawer, then turn the lights back on to clean the reaction cell, use methanol or DI for cleaning.. You may also need to replace the PMT filter, especially if it is obvious that a lot of ozone corrosion has occured on the filter.  Also be careful with the post-ozone restrictor that is inside the reaction cell, it should not be bent.

If the previous poster is right and you have a post-ozone restrictor problem, you can remove the post ozone restrictor and measure the flow coming out the end of the restrictor. It is supposed to be between 20-30 mL/min. The post-ozone restrictor is a P/N that you can replace.

Lastly when was the last time you replaced your ozone generator? Other than signal issues, you can visually inspect your ozone generator to determine if it has failed (or failure is imminent). The tube inside the generator will change from gray to dark brown/orange as it fails.