5. What is the conductivity range of the SureSense+?
Unfortunately, the conductivity of a liquid on its own does not give us enough information from which to assess if the SureSense+ will work in an application. The following notes are an attempt to provide a “rule of thumb” to help to evaluate an application.
The SureSense+ range is calibrated in resistance from 0 to 100% which is equivalent to a measurement range of 100 ohms to 100K ohms. A measure of the conductivity of the liquid, which is generating the foam gives us an idea of how easy the foam will be to measure. Conductivity is measured in millisiemens per centimetre (mS/cm) or microsiemens/centimetre (uS/cm). Technically it is possible to measure the effective conductivity of foam, but it is a complicated task and best avoided. However, the conductivity of the liquid below the foam, together with the tank geometry, gives us an idea of how easy measuring the foam will be. Conductivity alone is not enough as we need to know the geometry of the measurement system comprising the probe in the tank. In practice, the diameter of the tank (assuming that it is metal) and the conductivity gives us a good approximate guide. The other issue which affects the foam measurement is its density based on the liquid content: this is always difficult to estimate and can vary from less than 0.1% liquid up to 5% for a dense foam.
A simple estimate should help to determine if the SureSense+ will work or not in an application in a metal tank. This estimate is based on conductivity and the vessel geometry and ideally an idea of the foam density. The following data is needed:
- The conductivity of the liquid - uS/cm
- The diameter of the tank or pipe - cm
- The diameter of the probe - 12 mm or 20 mm
- Ideally an idea of the approximate foam density (if unknown assume 1%)
If the conductivity is below 400 uS/cm, then use Figure 1, otherwise, use Figure 2.
Using the conductivity and the tank diameter plot a point on one of the graphs below. If the point falls below the line for the probe size, then foam can probably be measured. If the point falls above, then the foam may not be measured. For example: for a 12 mm probe in a 50 cm diameter tank with a liquid conductivity of 320 uS/cm, the point falls below the blue 12mm line in
Figure 1. This indicates that the SureSense+ will work in this application for typical foam. If the conductivity were 300 uS/cm or less, then it would not work. This estimate is approximate, based on the average foam density of 1%, which would be denser than washing up type foam but less dense than Guinness foam.
Please consult a Hycontrol representative if you have any queries.