ICE 420 - Instrumentation and Control Engineering C3

Measurement

________ involves determining the magnitude or quantity of a specific variable by comparing it to a standard or predefined unit.

It provides a numerical value or result that quantifies the variable being measured.

Detection

focuses on identifying the existence or presence of a specific variable without necessarily quantifying it.

It is more about determining whether the variable is present or absent.

Detection instruments

_________ are designed to provide a simple indication of presence rather than giving detailed measurements.

(e.g., alarms or signal outputs)

DIAGRAM

BEST FUNCTION OF ANALOG MEASURING DEVICES

1. Accurate Representation of Input

2. Proportional Input/Output Relationship

3. No effect of External Factors

BASIC CHARACTERISTICS OF A MEASURING ELEMENT

Accurate Representation of Input

The measuring element must accurately detect and reproduce the input variable without distortion, ensuring the output is a true reflection of the process variable

Proportional Input/Output Relationship

The input (process variable) and the output (analog signal) should maintain a proportional relationship, allowing for consistent and predictable measurement performance.

No effect of External Factors

The measuring element should not be influenced by external factors like temperature, humidity, or vibrations, ensuring reliable and error-free measurements.

• Range

• Span (of a range)

DEFINITIONS

Range

The limit or extent of variation. The lower limit is called LRV & the upper limit is called URV.

--- 0 to 400°C

Span (of a range)

The number of units between two limits, the LRV and URV.

--- Span = URV - LRV

1. Analog Signal

2. Digital Signal

STANDARD INSTRUMENTATION SIGNALS

analog signal

An ________ is a continuous signal that can take any value within a range and does not have discrete positions or states.

It varies smoothly over time, representing changes in a process variable.

(e.g., voltage, current, or pressure).

Digital Signal

A ________ uses binary digits (s and 1s) to represent data.

It operates in discrete steps or states, making it suitable for representing continuous values or discrete conditions in a process control system.

CONTINUOUS PROCESS MEASUREMENT

It refers to the ongoing, real-time monitoring and measurement of a process variable, where data is continuously recorded and updated without interruption.

This type of measurement is crucial for systems that require constant oversight, such as industrial processes involving temperature, pressure, flow, or level control.

Continuous measurement

________ ensures that the process operates within specified limits, allowing for real-time adjustments and ensuring efficiency, safety, and quality.

(a) Sensor

(b) Transmitter

(c) Transducer

TYPES OF MEASURING ELEMENTS

Sensor

The component of an instrument loop that initially detects the value of a process variable and adopts a corresponding, predetermined, and intelligible state or output.

It is an integral part of the loop, sensing the process variable, assuming a specific state, and generating an output signal that is indicative of or proportional to the process variable.

Transmitter

A device that senses a process variable via a sensor and generates an output whose steady-state value changes according to a predetermined function of the process variable

Transducer

A device that receives information in the form of physical quantities, modifies the information or its form (if necessary), and produces an output signal.

The term "______" is general and can refer to primary elements, transmitters, relays, converters, or other devices.

Specifically, a transducer converts a mechanical signal into an electrical signal.

TRUE

Transducers and transmitters are similar, but the key difference lies in the type of electrical signal they output. A transducer typically outputs in volts (V) or millivolts (mV), while a transmitter uses milliamps (mA).

1. Direct Method

2. Inferential Method

METHODS OF MEASUREMENTS

Direct Method

In this method, the process variable is directly measured in units that represent its basic nature, providing an immediate and straightforward measurement of the variable itself.

The measurement for level in this tank is measured directly in units of height since the level of the tank is seen directly through a sight glass (scaled) representing the current level of the tank.

Inferential Method

This method involves the indirect measurement of a process variable using another related variable.

- For example, the level of liquid in a tank can be measured based on the hydrostatic pressure below the tank. Since pressure is directly proportional to the liquid height, any change in the liquid level will cause a proportionate change in the pressure reading, which is then used to infer the liquid level.

1. Single Point Type Measurement

2. Continuous Type Measurement

TYPES OF MEASUREMENTS

Single Point Type Measurement

This measurement method depends on a fixed value of the process variable. The reading is indicated as either "high" or "low."

- For example, Sensor A and Sensor B will only trigger when the process variable reaches the set high or low levels, respectively, activating based on those specific points

Continuous Type Measurement

This method provides ongoing measurement of a process variable, allowing for continuous monitoring.

- For instance, a magnetic float can indicate the current level measurement through a sight glass, showing the level within its range regardless of the actual height of the liquid in the tank. This enables real-time monitoring of the liquid level, providing continuous updates.

discrete variable

In engineering, a ____________ or measurement refers to a condition that has distinct, binary outcomes, such as true or false.

discrete sensor

A ________ is designed to indicate whether the measured variable is above or below a specified setpoint.

These sensors are often in the form of "switches," which activate when the measured quantity exceeds or falls below a predetermined value.

PROCESS SWITCH

It is a type of measuring element that monitors and controls a process by switching states based on predetermined conditions or setpoints.

It is commonly used in industrial control systems for regulating processes

normal

The "_________" status of a switch refers to the condition of its electrical contacts when there is minimal physical stimulus applied.

1. Normally-Open Status

2. Normally-Closed Status

"NORMAL" STATUS OF A SWITCH

Normally-Open Status

A __________ is one where the contacts remain open (disconnected) when no physical stimulus is applied.

Normally-Open Status

The switch only completes the circuit and allows current to flow when the switch is pressed, causing the contacts to close.

- For example, a lamp will only energize if someone presses the switch, which closes the normally-open contacts. In the electrical industry, normally-open switches are sometimes referred to as Form-A contacts.

Normally-Closed Status

A ________ is one where the contacts remain closed (connected) when no physical stimulus is applied, allowing current to flow.

Normally-Closed Status

The circuit is interrupted when the switch is pressed, causing the contacts to open and stop the current flow.

- For example, a lamp will energize as long as the switch is left alone, but it will turn off if anyone presses the switch. In the electrical industry, normally-closed switches are sometimes referred to as Form-B contacts

1. Hand Switches

2. Limit Switches

3. Proximity Switches

4. Pressure Switches

5. Level Switches

6. Temperature Switches

7. Flow Switches

TYPES OF SWITCHES

hand switch

A ______ is an electrical switch actuated by a person's hand motion. This may take a form of toggle, pushbutton or rotary.

limit switch

A _________ 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.

Proximity Switches

A ________ detects the proximity (closeness) of an object. By definition, these switches are noncontact sensors, using magnetic, electric or optical means to sense the proximity of objects.

pressure switch

A __________ detects the presence of fluid pressure. _______ often use diaphragms or bellows as the pressure sensing elements, the motion of which actuates one or more switch contacts.

Level switch

A __________ detects the level of liquid or solid (granules or powder) in a vessel. ___________ often use floats as the level-sensing element, the motion of which actuates one or more switch contacts.

Temperature switch

A ____________ detects the temperature of an object. __________ often use bimetallic strips as the temperature-sensing element.

Flow switch

A _______ detects the flow of some fluid through the pipe. ________ often use "paddles" as the flow-sensing element, the motion of which actuates one or more switch contacts.

Receiving elements

___________ in an instrument system are components that receive signals from measuring instruments and process them into usable information for the operator.

These elements can include indicators, recorders, controllers, alarm units, or any combination of these, depending on the system's requirements.

indicator

An _________ is a receiving element that receives the process variable (PV) signal from the measuring element and displays the value of the measured variable in actual engineering units.

TRUE

According to the ISA definition, an indicator is a measuring instrument that visibly shows only the present value of the measured variable. It provides real-time information to the operator about the current status of the process.

1. According to the Display

2. According to the inputs

3. According to the scale

4. According to Mounting

TYPES OF INDICATORS

Analog, Digital, Bar graph

According to the Display

Scanning, Multi-channel

According to the inputs

Horizontal, Vertical, Semicircle, Quarter-circle

According to the scale

Control room mounted; Field mounted

According to Mounting

recorder

A __________ is a receiving element that receives the process variable (PV) signal from the measuring element and stores the historical values of the variable in a graphical and/or tabulated manner.

recorder

This data can be recorded on paper or saved to memory media.

_______ may also include a display to show the measured values in real-time, but their primary function is to provide a historical record of the process variable for analysis and tracking.

TRUE

According to the ISA definition, a recorder is a measuring instrument that records the values of the measured variables.

1. According to the recording format

2. According to the inputs

3. According to the construction

TYPES OF RECORDERS

Trend, Log

According to the recording format

multi-channel, multi-point, npoint

According to the inputs

Circular-chart, Sripchart, Paperless, Data logger

According to the construction

1. As a guide to the operation of a process by observation of the trend of variables.

2. As a troubleshooting function by analyzing or locating the possible source of the problem.

3. As a source of management information in measuring past performance

IMPORTANCE OF RECORDING

1. According to the capacity

2. According to display

3. According to size

4. According to technology

TYPES OF CONTROLLERS

Single-loop, multi-loop

According to the capacity

Analog, Digital, Recording, Blind

According to display

1/4 DIN, 1/2 DIN

According to size

Pneumatic, Electric, Electronic, Digital, Microprocessor-based.

According to technology

1. Local, Internal

2. Remote, External, Cascade

3. Program Or Profile - a setpoint that changes automatically with respect to time, by a pre-arranged instruction during configuration.

TYPES OF CONTROL SETPOINTS

Local, Internal

A setpoint adjusted by the operator

Remote, External, Cascade

a setpoint adjusted by signal input to the controller

Program Or Profile

a setpoint that changes automatically with respect to time, by a pre-arranged instruction during configuration.

(a) Typical Control Panel with Conventional Instruments

(b) Computer-based Process Control Systems

Program Or Profile

- Programmable Logic Controller (PLC)

- Distributed Control System (DCS)

- SCADA Systems

Computer-based Process Control Systems

Programmable Logic Controller (PLC)

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 (DCS)

are controllers that, in addition to performing control functions, provide readings of the status of the process, maintain databases and advance manmachine-interface.

SCADA Systems

are used to monitor and control a plant or equipment in industries such as telecommunications, water and waste control, energy, oil and gas refining and transportation.

final control element

The __________ is a critical component of a control system that directly acts to adjust the manipulated variable based on the signal received from the controller.

Its primary function is to implement the corrective action calculated by the controller to maintain the process variable at the desired setpoint.

actuator

An _______ is a component of the final control element that converts the signal from the controller into a physical action to create the desired change.

It is responsible for causing the movement or adjustment required in the final control device, such as opening or closing a valve, positioning a damper, or adjusting a motor

Actuators

_______ are typically powered by pneumatic, hydraulic, or electrical energy and serve as the driving force behind the physical operation of the control system.

Control valves

________ are a type of final control element designed to manipulate the flow rate of gases or liquids within a system.

They operate by adjusting their position (e.g., opening or closing) in response to the actuator's signal, thereby regulating the flow to maintain the desired process conditions.

Control switches

_________ , on the other hand, are used to manipulate electrical energy entering a system. Instead of controlling fluid flow, they act as binary devices (on/off) to enable or disable electrical circuits, often used for processes requiring discrete control rather than continuous modulation.

The following are different values that represent the typical ranges for different types of instrumentation signals:

--

- English Units: 3 to 15 psi

- Metric Units: 0.2 to 1.0 bars (or Kg/cm^2)

- This range is commonly used for pneumatic systems where air pressure is used to transmit signals.

PNEUMATIC OR AIR PRESSURE

- Current: 4 to 20 mA DC

- Voltage: 1 to 5 V DC

- These ranges are widely used in industrial instrumentation for transmitting signals through electrical current or voltage. The 4 to 20 mA range is especially popular for transmitting measurements like temperature, pressure, and flow, where the current increases as the variable increases.

ELECTRICAL OR ELECTRONIC

Linear interpolation

is a method used to calculate intermediate values between two known points.

It is widely used in instrumentation to scale an input value to an output range (e.g., 4 -20 mA or 0 -100%)

X2 = (Y2 - Y1) (X3 - X1) / (Y3 - Y1) + X1

Y2 = (X2 - X1) (Y3 - Y1) / (X3 - X1) + Y1

The formula for linear interpolation is: