The importance of flow measurement has been increasing in the past few decades. In food and chemical processes the quantity of the added fluid components has to be measured. In other kind of processes (e. g. electric power generation) the fluid stream is the main source of energy and it has to be measured in order to control the process properly. There are also flow measurements which have a direct financial effect, e. g. companies distributing drinking water and district heating bill the consumers based on data measured by flow meters. It's easy to realize that inaccurate measurements may cause remarkable property damage. Thus to avoid this, the calibration of the flow measuring devices is substantial and it's also often specified by the authorities.
Gamma Digital Ltd. has a flow meter calibrating laboratory which is able to calibrate flow meters up to diameters of 700 mm with volume flow rate 4500 m3/h. The current equipments of the laboratory are obsolete and need to go over a fundamental modernization. Throughout the development process the past experiences and the future requirements of the system have to be taken in consideration.
The calibration needs to be done with a nearly constant flow rate. This is a requirement for valid calibration process. The maximum deviation from the desired flow rate is determined by the regulations of the Hungarian Trade Licensing Office (MKEH). For the purpose of closed-loop controlling there are control valves installed in the different pipe sections. The controlled process is nonlinear and it's parameters change during the measurement as the result of the set-up of the laboratory.
The aim of my thesis work was creating the model of the laboratory, thereafter choosing and implementing a control solution with the use of the created model that fulfills the requirements.
First I got familiar with the laboratory set-up and developed the model of the process using the principles of fluid mechanics. Based on the previous model I created the computer model and used it to test PID control solutions.
At the end of the semester the new control system was implemented. I participated in selecting the new system elements, and created the flow controlling task in the controller's program. Finally I took measurements using the new controlling system and managed to specify a PID control solution that fulfills the requirements.