Funda3 ppt1

• Single Point Type

  ➢the measurement depends on a fixed value of the process variable.
• Continuous Type

  ➢is the measurement of a process variable indirectly by using another variable.
• Instrument Range - refers to the capability of the instrument to measure a variable.
• Calibration Range - refers to the set of values within the instrument measuring range where the scaled output; 4-20 mA, 3-15 psi or 1-5 V is set during calibration.
• Instrument Span

  It is the distance (or difference) between the upper range value (URV) and lower range value (LRV).
• Upper Range Value - is the highest value of the measured process variable that the output of a transmitter is currently configured to measure.
• Lower Range Value is the lowest value of the measured process variable that the analog output of a transmitter is currently configured to measure.
• Electrical switch contacts are typically classified as either normally-open or normally closed, referring to the open or closed status of the contacts under “normal” conditions.
• Normally-open status are sometimes referred to in the electrical industry as form-A contacts
• Normally-close status are sometimes referred to in the electrical industry as form-B contacts.
• A hand switch is an electrical switch actuated by a person’s hand motion. This may take a form of toggle, pushbutton or rotary.
• A limit switch detects the physical motion of an object by direct contact with that object. A limit switch will be in its “normal” status when it is not in contact with anything.
• A proximity switch detects the proximity (closeness) of an object. By definition, these switches are non-contact sensors, using magnetic, electric or optical means to sense the proximity of objects.
• A pressure switch detects the presence of fluid pressure. Pressure switches often use diaphragms or bellows as the pressure sensing elements, the motion of which actuates one or more switch contacts.
• A level switch detects the level of liquid or solid (granules or powder) in a vessel. Level switches often use floats as the level-sensing element, the motion of which actuates one or more switch contacts.
• A temperature switch detects the temperature of an object. Temperature switches often use bimetallic strips as the temperature-sensing element.
• A flow switch detects the flow of some fluid through pipe. Flow switches often use “paddles” as the flow-sensing element, the motion of which actuates one or more switch contacts
• An on/off valve is the fluid equivalent of an electrical switch: a device that either allows unimpeded flow or acts to prevent flow altogether.

  Valve styles commonly used for on/off service include ball, plug, butterfly, gate and globe.
• Controller

  ➢a device that receives data from a measurement instrument , compares that data to a programmed setpoint, and, if necessary, signals a control element to take corrective action.
• Programmable Logic Controller – usually computers connected to a set of input/output (I/O) devices. The computers are programmed to respond to inputs by sending outputs to maintain all processes at setpoint.
• Distributed Control System – are controllers that, in addition to performing control functions , provide readings of the status of the process, maintain databases amd advance man-machine- interface.
• Final Control Element

  ➢ The part of the control system that acts to physically change the manipulated variable.

  ➢Typically used to increase or decrease fluid flow.
• Actuator

  ➢ the part of a final control device that causes a physical change in the final control device when signalled to do so.
• Control Valves

  ➢manipulate the flow rate of gas or liquid; whereas, the control switches manipulate the electrical energy entering a system.