What is the TB820D (Right Angle Scattered Light Turbidity Detector) head tank difference between D1, D2 and D3? Is head tank necessary?

We strongly recommend using head tank in any case for stable measurement. If your facility has enough pretreatment and there are no bubbles, you can install the TB820D without head tank.
D1 pressurized head tank is suitable for under 2 NTU measurement case and D3 is suitable for over 2 NTU measurement case. D2 Simple head tank is reasonable, but it can use only for between 2-10 NTU measurement case.