What kinds of instruments are used in oil refinery?
They can be roughly divided into four kinds: (1) measuring instruments including sensors for measuring all kinds of process parameters and transmitters, (2) display instruments for both analogue and digital information display, (3) controllers including electric and pneumatic controllers, (4) actuation system including pneumatic, electric and hydraulic actuators.
What are the functions of each kind of measuring instruments?
Measuring instruments include sensor, transducers and transmitters. They are used to measure all kinds of process parameters and convert the measured signals into the signals which can be transmitted and displayed or into standard signals.
The display instruments include indicators, recorders, printer, CRT display, industrial TV sets and annunciators. They are used to provide the operators and managers with the signals from the sensors and transmitters. They can perform the functions of indication, recording, digital display, printing tables, graphic display and sound and light annunciation.
The conversion and transmission instruments including data highway and standard interfaces are used fro transmit information. They can be used to convert electric signal into pneumatic signals, analogue signals into digital signals.
The functions of a control instrument and control system are used to process the signals both from the measuring instruments, conversion and transmission instruments and that input by the operators and then send out control signal. This is the core of the automatic control system. They include sequential controller, programmable logic controller (PLC), industrial computer control system.
Actuation device includes an actuator and a control valve. Their function is to receive the instructions from both controllers and operators and output signals of certain power for operation and control of the production processes. They include electric, pneumatic and hydraulic actuators and all kinds of relays and other electronic devices.
The control systems need auxiliary equipment such as consoles, instrument control panel, stabilized power supply, compressed air and purification facilities. A control system consists of two parts: one is automatic control instruments consisting of sensors and transmitters, controllers, actuators; and the other is the equipment where the process parameters need to be controlled which is also called controlled object.