measuring control, open loop control apparatus and closed loop feed-back control and monitoring apparatus particularly for utilization in the chemical, petrochemical, thermal, and electrical technology; analysing apparatus, particularly automatic gas and liquid analysers; ph measuring instruments, instruments for measuring conductivity, measuring transducers (sensors) for physical and chemical properties of gasses and liquids; registering apparatus particularly line-writers, dot printers, light beam oscillographs, registration instruments for analog plotting of measuring data; fault (error) printers, registration and monitoring apparatus for special rates; measuring transducers for temperature and mechanical variables such as rotational speed and position; measuring transducers and measuring transformers particularly for pressure, differential pressure, flow-throughput, moisture content, state-of-filling (level); measuring transformers for d.c. voltage, electrical variables, resistance, frequency; apparatus for remote transmission of measuring values, measuring value evaluating equipment; relays, electrical and electronic measuring and power amplifiers, switching relays, time relays and control apparatus, follow-up (servo) control apparatus, actuators; calculating machines and computers and data processing apparatus and systems composed thereof; analog and digital computers for processing measuring data; automatic controllers, particularly electromechanically, electrically electronically operating steady state and on/off and digital controllers with optical control input; controllers in industry, control systems being comprised of mutually attuned (adjusted, integrated) electrical and electronic apparatus within a functional chain of units comprised essential of measuring transducer, measuring transformer, controller, power amplifier, adjustment drives and actuators, for control of industrial plants and including associated switch panels, switching cabinets and consoles (desks) pertaining thereto; apparatus for measuring the state of filling (level) and density by means of radioactive radiation, measuring apparatus using nuclear radiation, transducer for measuring radioactive isotopes and equipment made thereof; measuring instruments particularly instruments operating electromechanically, electrically or electronically and electronic analog and digital measuring instruments being controlled by optical input; multipurpose measuring apparatus, measuring bridges, compensators, frequency measuring instruments; precision measuring instruments; measuring apparatus for locating faults; accessories for measuring apparatus and for automatic controllers; namely, measuring resistances, measuring capacitors, measuring inductances, remote controlled st point adjusters, remote control operating equipment, data display instruments and stabilized power supply apparatus