Proper plant control and operation has to be based on measurements of process data at different locations within the process. The design of the instrumentation network is therefore an important step in the design phase of a given process. An advanced instrumentation network design should not only allow process control on a minimum data basis but should enable the plant operator to gain more insights into the functionality and capabilities of his process. For this purpose in-process balancing based on a suitably configured instrumentation network is necessary. To make full use of the measurements the data has to be processed by data reconciliation methods. In the present work an earlier approach by Chmielewski et al. (2002) has been applied to solids processes. This paper shows how the selected approach can be adopted to the measurement and processing of distributed variables, e.g. particle size and densities. An optimal instrumentation with regard to investment cost can be found that ensures that all necessary data for the reconciliation problem can be collected. The application to solids processes is illustrated with the examples of a simple screening-crushing process and a hydrocyclone cascade.