The simple-design low-cost microprocessor-based controller RT28 combines the advantages of the microprocessor devices with the high reliability of analog controllers. It is available with 96x48, 48x96, and 96x96 mm DIN-sized front panel and can be equipped with up to 2 control relays. To control its outputs, RT28 may utilize either ON/OFF (heat/cool) duplex or PD control algorithm. The ON/OFF control algorithm allows flexible programming of the action of each relay for solving variety of problems. The PD algorithm results in PI control when used to control motorized valve actuators without position feedback. The reliable operation even in the presence of electromagnetic disturbances and the attractive price also account for the success of the RT28 controller.