The qualities of the process water and the solids to be measured will affect the effective maximum level that can be measured. For a ‘clean’ application (such as silica in clean water), we could expect to be able to measure up to 50% solids (500,000 mg/l) reliably. On the opposite side of the spectrum, black sludge in a wastewater plant may have a reliable limit as low as 5% (50,000 mg/l). Experience shows that in most wastewater works the upper limit is around 8% solids (80,000 mg/l).