Jakub Lev

The mathematical model of experimental sensor for material distribution detecting on the conveyor

Much research has already been devoted to various electrical capacitance techniques for determining the flow of material or to define the material distribution. Simple electrical capacitive throughput sensors, but also very complex electrical capacitance tomograph sensors were tested. An interesting compromise may be segmented capacitance sensor (SCS). In this paper, a mathematical model of SCS is verified. Two mathematical models are compared. The first model simplifies the problem by the use of the electrostatic field. Using the second model a variable electric field at low frequencies is described. It was found that, for an easier description of the SCS electric field, this field can be considered as the electrostatic field. Measurements carried out, for the most part supported the correctness of the mathematical model. Some deviations were probably caused by transferring the problem to 2D.

Segmented Capacitance Sensor with Partially Released Inactive Segments

Abstract Material throughput measurement is important for many applications, for example yield maps creation or control of mass flow in stationary lines. Quite perspective can be the capacitive throughput method. Segmented capacitance sensor (SCS) is discussed in this paper. SCS is a compromise between simple capacitive throughput sensors and electrical capacitance tomography sensors. The SCS variant with partially released inactive segments is presented. The mathematical model of SCS was created and verified by measurements. A good correspondence between measured and computed values was found and it can be stated that the proposed mathematical model was verified. During measurement the voltage values on the inactive segments were monitored as well. On the basis of the measurement there was found that these values are significantly influenced by material distribution.

Capacitive throughput sensor for plant materials Effects of frequency and moisture content

Novel laboratory capacitor was developed.Detailed information on the influence of frequency on capacitive throughput sensor function is provided.The sensor was less sensitive to material moisture content changes at lower frequencies.The sensor was also less sensitive to the material moisture content at lower filling levels. The empirically determined material moisture content and frequency are among the main parameters that affect the dielectric properties of plant material. When using a capacitive sensor to measure the throughput of plant materials, an unexpected change in the measured material moisture content can result in significant error. This problem can be minimised by using a suitable electric field frequency. Thus, we studied the effect of various frequencies on capacitive throughput sensor behaviour.A novel laboratory capacitor was developed, and two sets of experiments using balsa blocks as plant material were performed. We confirmed that the dependence of sensor output voltage on the measured material moisture content could be described by S-shaped curves with two breakpoints between three sections. The first and third sections were characterised by a low influence of material moisture content on the capacitive throughput sensor output signal, whereas the moisture content had a larger influence in the second section. The shapes of the calculated curves were influenced by both the frequency of the electric field and the level of sensor filling. The sensor was less sensitive to moisture content changes when lower frequencies were employed and when the fill level was lower.