Studied by 34 people
Instrumentation
branch of physics which deals with the measuring, monitoring, and controlling variables in a process industry
Instrument
device that measures, monitors and control process variable
Instrumentation based on Industrial application
a collection of instruments, devices, hardware or function or their application for the purpose of measuring, monitoring or controlling an industrial process or machine, or any combination of those
PICS
Philippine Instrumentation and Control Society
SAMA
Scientific Apparatus Manufacturers Association
Critical, Non-critical, reference only
Classification of Instruments
Critical
An instrument which, if not conforming to specification, could potentially compromise product or process quality
Non-critical
An instrument whose function is not critical to product or process quality, but whose function is more of an operational significance
reference only
function is not critical to product quality, not significant to equipment operations, and not used for making quality decisions
Control
refers to regulation, command, or direction of all aspects of the process
Manual Control and Automatic Control
2 types of control
Process
any operations or sequence of operations involving a change of energy, state, composition, dimension or other properties that may be defined with respect to a datum/data. It also refers to the method of changing or refining raw materials to create end products.
Process control
the regulation or manipulation of variables influencing the conduct of a process in such a way as to obtain a product of desired quality and quantity in an efficient manner
System
an arrangement, set, or collection of physical components connected or related in such a manner as to form and/ or act as an entire unit.
Control system
an arrangement of physical components connected or related in such a manner as to command, direct, or regulate itself or another system
Instrumentation system
an arrangement of two or more instrument connected together to perform a unified task.
Control Loop
A process management system designed to maintain a process variable at a desired set point
Open control loop and Closed control loop
2 types of Control loop
Open control loop
Exists when the process variable is not compared, and action is taken not in response to on the condition of the process variable.
Closed control loop
exists when a process variable is measured, compared to a set point and action is taken to correct any deviation from setpoint.
Setpoint
a value for a process variable that is desired to be maintained or any input variable that sets the desired value of the measured variable
Process, measuring element, receiving element, and final control element
Elements of the instrument loop
process variable
any variable property of a process
Controller output
outputs signal generated in response to a change of a process variable
manipulated variable
a process variable linked to the controller output that is used to influence the measured variable
discreet field mounted
Computer function field mounted
shared display field mounted
PLC field mounted
Discreet located in main control panel
Shared display located in rear of main control panel
PLC located in local control panel
CF located in rear of local control panel
Pressure, level, flow, temperature
Major Process Variable
Instrumentation and control loop or instrument loop
A combination of two or more instrument or control functions arranged so that signal pass from one to another for the purpose of measurement and/ or control of a process variable
Measurement
The determination of the magnitude of a variable (value)
Detection
the determination of the existence or the presence of a variable
output represent the input faithfully
linear input/output relationship
no effect of temperature and others
Basic characteristics of a measuring element
Range
The limit or extent of variation. The lower limit is called LRV and the upper limit is call URV
Span
The number of units between two limits, the LRV and URV.
(Span = URV - LRV)
Analog signal and Digital signal
Standardized signals
Analog signals
A signal that has no discrete positions or states and changes value
Digital Signal
a signal that generates or uses binary digit signals to represent continuous values or discrete states
3 to 15 psi
Pneumatic or air pressure (English)
0.2 to 1.0 bars or kg/cm^2
Pneumatic air pressure (Metric)
4 to 20 mA dc
Electrical or electronic (current)
1 to 5 V dc
electrical or electronic (voltage)
Sensor, transmitter, transducer, process switch
Types of measuring elements
Sensor
An integral part of instrument loop or instrument that first senses the value of a process variable, and that assumes a corresponding, predetermined, and intelligible state or output indictive or proportional to the process variable.
Transmitter
A device that senses a process variable through the medium of a sensor and has an output whose steady-state value varies only as a predetermined function of the process variable.
Transducer
Translate mechanical signal into an electric signal. A general form of a device that receives information in the form of one or more physical quantities, modifies the information and/or its form, if required and produces a resultant output signal.
Volts or millivolts
A signal sent by a transducer
Milliamps
A signal sent by a transmitter
Expensive, very accurate, very rugged, repairable, adjustable range, standard signal output
Characteristics of a Transmitter
Low cost, not so accurate, not so rugged, not repairable, fixed range, different outputs by the manufacturers
Characteristics of Transducer
Converter
A device that converts one type of signal into another type of signal. (current into voltage, analog to digital
Direct method and inferential method
Methods of measurement
direct method
The process variable is measured in units that represent the basic nature of that variable itself
inferential method
the measurement of a process variable using another variable
Single point type and continuous type
Types of measurement
Single point type
the measurement depends on a fixed value of the process variable and reads either as high or low
Continuous type
A type of measurement of a process variable in which the process variable is measured indirectly or 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; 4-20mA, 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
the highest value of the measured process variable that the output of a transmitter is currently configured to measure.
Lower range value
The lowest value of the measured process variable that the analog output of a transmitter is currently configured to measure
Discreet sensors
Typically take the form of switches, built to trip when the measured quantity either exceeds or falls below a specific value. These devices are less sophisticated than so called continuous sensors.
Discrete process measurement
Measurement process in which sensors are only able to indicate a true or false condition.
Normal status of a switch
The status in which electrical contacts are in under a condition for minimum physical stimulus.
Normally-open status
The lamp will energize only if someone pressed the switch holding it in a closed position. It is also referred to as Form-A contacts.
Normally-closed status
A lamp will energize only if the switch was left alone, but it would turn off if anyone pressed the switch. It is also referred to as form-B contacts
Hand switches
An electrical switch actuated by a person’s hand motion. This may take a form of toggle, pushbutton or rotary.
Limit switches
detects the physical motion of an object by direct contact with that object. This switch will be in its “normal” status when it is not in contact with anything.
Proximity Switches
detects the closeness of an object. These switches are non-contact sensors, using magnetic, electric, or optical means to sense the (closeness) of an object
Pressure switches
It often use diaphragms or bellows as the sensing elements, the motion of which actuates one or more switch contacts.
Level switches
These switches usually use floats as sensing element, the motion of which actuates one or more switch contacts
Temperature switches
These switches often use bimetallic strips as sensing element.
Flow switches
A switch that uses paddles as sensing element, the motion of which actuates one or more switch contacts
Discrete Control Element
A device that either allows unimpeded flow or acts to prevent flow altogether
Controlling element
known as the brain of the control system. It performs appropriate functions for maintaining the desired level (set point) of parameters to restore quality and rate production
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 and Distributed control system
Common examples of controller
Programmable Logic Controller
Usually computers connected to a set of Input/output devices which are programmed to respond to inputs by sending outputs to maintain all processes at setpoint.
Distributed Control System
controllers that, in addition to performing control functions, provide reading of the status of the process, maintain databases, and advance man-machine interface.
Feed forward
Correcting an action before the process
Feed back
Correcting an action after the process
Basic Process Control System
BPCS
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 the final control element that causes a physical change in the final control device when signaled to do so.
Control Valves
Manipulate the flow rate of gas or liquid; whereas control switches manipulate the electrical energy entering a system.
Globe valves
A linear motion valve used to stop, start, and regulate fluid flow. The three primary body designs for this valve are Z-body, Y-body, and Angle.
Recommended for throttling application, Good for frequent operation, easy to repair
Advantages of Globe valve
Flow path causes a significant pressure drop, more costly than alternative valves
Disadvantages of Globe Valves
tee, angle, wye
Types of globe valves
Tee
most common body type for a globe valve. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the horizontal line. This design has the lowest coefficient of flow and highest pressure drop. They're used in severe throttling services, such as in bypass lines around a control valve. When pressure drop is not a concern and throttling is required, this globe valve design is a good solution.
Angle
The ends of this globe valve are at a 90° angle allowing fluid to flow in a single 90° turn. This valve is used for applications that have periods of pulsating flow because of their ability to handle "the slugging effect" which naturally occurs with a pulsating flow.
Wye
This type is an alternative for the high pressure drop commonly found in globe valves. The seat and stem are at a 45° angle which provides a straighter flowpath when fully open and offers the least resistance of flow. This design is commonly used for throttling during seasonal or start-up operations.
Gate Valves
Flow is controlled by raising or lowering the valving element. They are not usually used to regulate flow because the valving element can be damaged when in the partially open position
Solid Wedge Gate Valve
the most common & widely used disk type because of its simplicity and strength. May be installed in any position, and it is suitable for almost all fluids.
Note
Flashcard