Please we have a tough interface level measurement application of equalization tank that has oily water in the bottom with average level of near 3000mm and on top of it an oil layer of near 300 to 500 mm. We need to measure this water interface level. Before we were using enraf servo, but it is unreliable as the water is unclean (oily water, dirt) so the stilling well was always clogging. We removed it then again the displacer giving in correct reading. So, we need to see what is the most suitable level technology that we can use for this dirty water interface lengthy tank (near 5 meter). Appreciate your professional advice.
We have used Rosemount 5300 Guided Wave Radar (GWR) for interface. If there are no internals or agitators, a stilling well would not be required. The dielectric constant of the would have to be greater than 1.4. The 5300 series is able to sense lower than 2.00 dielectric constant. Many pure oils are around 2.0 water is much higher. A nuclear interface would work also, but are much move expensive and may require a certified nuclear licensed person on site.
A Toroidal conductivity probe will read High if the interface is above the probe. Low if it's below, there is no doubt.
If you put the probe at the level you want to control the interface, it's a simple matter of logic to control the level of the dirty water. It will also differentiate between an emulsion layer with a conductivity reading in between.