Instrumentation Final

What elements do electronic process control systems use?

Sensors and transmitters, controllers, Final control elements, and indicating, interfacing, and accessory devices.

What is a Distributed control system (DCS)?

What’s used in the lab. Has a network, power supply, Input and output, modules, and workstations. Used to automate and manage entire plants or complex continuous processes from a centre control room

What are servers?

Central computer that holds a collection of data and software programs allowing users to share these data and applications

What kind of control loops can process learning controller (PLC) run?

Can run PID control loops

What is the sensor bus network?

Contains simple devices like switches, push buttons and proximity sensors

What is the device bus network?

More complex devices such as temperature transmitters and variable speed drives

What are field bus networks?

Interconnects smart devices such as controllers and PLCs

How does a smart transmitter work?

Has built in microprocessor that handle both digital and analog signals. Can receive multiple inputs and outputs, and signals alarms and error conditions

What is a display terminal?

Graphical indication like historical trending, and representation of a controller automatic/manual/cascade

What is an example of a basic control system?

Main temperature sensor measures the hot water supply, the controller will vary the supply water temperature set point as a function of the outdoor air temperature

How does a basic control system work?

Controller analyzes the sensor data and sends a signal to the valve actuator to regulate the mixture of return and boiler water

What is manual?

Controller takes no automatic action. Only the output of FCE is controlled by operator

What is automatic mode?

Set point determined by the operator and the controller compares the PV to set point

What is cascade mode?

The output signal from one controller is the set point for the other

A DCS is a computer based control system, therefore it requires a __________ to work properly.

Digital input signal

What is the basic operation of a computer?

Takes in raw input data, processes it, converts it into meaningful information and presents the data in an understandable output format

What are the four components of a basic computer?

Input device, memory, cpu, and output devices

What are examples of process inputs?

Discrete voltage signals, analog transmitters (must be converted to digital to work with computer) and digital transmitters

How do digital outputs work?

Converted to analog through a digital to analogue converter to manipulate analogue FCE’s

What is a motherboard?

Circuit board that holds and allows communications between many of the components such as CPU

What is the central processing unit?

Contains complex circuitry which accept input numbers, perform calculations in accordance with a program, and output the results

What is computer memory?

Silicon integrated circuit that stores information by turning miniature circuits on or off. The amount of memory is equal to the number of circuits that can store information.

What are “bits”?

A silicon switch that are on/off. and groups of 8 bits are called bytes

What is random access memory (RAM)?

Used to store (write) or retrieve (read) information. Insufficient ______ can cause computers to slow down or stop functioning

What is Read only memory (ROM)?

Preserves program information even when the computer is powered off. Stores information permanently burned onto the memory chip

What is EPROM?

Type of re-programmable ROM which allows computers to be configured for particular applications

What is hard disk drive?

Data storage device used to store and retrieve data. Retains stored data even when powered off

What are plotters?

Large format printer used to produce engineering diagrams and schematics

What is a multiplexer?

Everything happens in a sequence and to ensure this happens, a _________ is used to select the correct computer input at the correct time

What is the power supply?

Converts low voltage AC to extra low voltage regulated DC power (115 VAC to 24 VDC)

How does signal input conversion work?

A digital equivalent is determined by adjusting an internal voltage in a number of digital steps until it matches as closely as possible to the input. The number is then passed to the CPU for calculation

How does signal output conversion work?

The digital number from a CPU switches a number of precision resistors from a regulated power supply and the switch combination determines the analog output signal

What is a full backup?

Complete copy of an entire dataset and provide the best data protection. Very time consuming and requires the most storage space

What is incremental backup?

Only changes the data since the last backup. Most storage efficient

What is differential backup?

Copies all data since the last full backup. Requires second most storage space

What does “and” mean in basic logic conditions?

“And” are things in series. You need to have this AND that otherwise boilers gets tripped

What does '“or” mean in logic conditions?

“Or” are things in parallel. You can have this OR that for function of the boiler

What is inventory control?

Originally why computers were used. Used to track inventory of raw materials, finished products and things delivered

What is maintenance management?

Computers are used to keep track of operating time for the plant equipment and maintenance schedules

What is plant management?

Possible that plant management will have access to a management computer where they can enter in a production value and then things will automatically change based on that

What are two position switches?

On/Off

What are multi position switches?

More than two positions. Can control different firing rates or put in automatic

What are momentary contact switches?

Makes a contact that opens right away. used to silence alarm horns

What are maintained contact switches?

Changes position when activated and stays in that position until actuated again (remote ECS in lab by door for example)

What are thermostats used for?

Maintain the temperature of a heated space or substance at the desired set point

What is a duct thermostat?

Controls the air temperature in ducts and plenums. 

What is a modulating thermostat?

Employs a bimetal strip, bellows, or remote bulb which is equipped with a special regulating mechanism (potentiometer) that adjusts circuit voltage in proportion to the measured conditions. Not a simple on/off switch

What are multi position thermostats?

Operates like an on/off but it has two or more switches that operate in sequence

How does a hygroscopic element humidity controller work?

Moisture sensitive nylon which increases in length when humidity increases. Change in length activates controller mechanisms which may be a switch for on/off or potentiometer for modulating

What are high pressure controllers?

Measure and control high pressure or vacuums which are measured in KPA or in mm of mercury

What are low pressure controllers

Measure and controls low pressure or vacuums and is measured in mm of water

How do pressure controllers work?

Contain a diaphragm where one side is exposed to the pressure to be controlled and the other to a reference pressure

What is an example of a pressure controller in the lab?

High and low fire mode controllers on saskatoon boiler

What are relays?

Device that controls a large amount of energy with only a small amount of energy. 

What is an example of a process of how a relay works?

Low voltage wiring goes to relay and activates it. Relay will be higher voltage which triggers a solenoid that has higher voltage requirement. Then takes small signal voltage and allows us to do/use things with higher voltage

How do variable resistors work?

Changes the resistance so that we can automatically adjust voltage and current in response to measure process conditions

What is a potentiometer?

Three terminal variable resistor used to vary control circuit voltage between zero and max voltage. These are used to change voltage

How does a rheostat work?

Two terminal variable resistor used for varying current in a circuit. Can be used to vary AC or DC signals

How does a thermistor work?

Thermally sensitive resistor who’s resistance changes with temperature. Can have either positive or negative temperature coefficient. 

What are thermistors used in?

Electronic circuits that handle temperature measurement, control and compensation

How does a photoresistor work?

Changes in resistance according to the amount of light that reaches its surface

What are examples of final control elements?

Valve actuators, damper drive motors, stepper motors and motor starters. 

What are final control elements used for?

Used to control level, pressure, flow, and temperature. Can be discrete (on or off/open or close, or fully modulating)

What are examples of what an electric thermostat can control?

Fuel valve on the supply line to the burner, electric relay that starts or stops a circulating pump or an electric valve in the supply line to steam or hot water radiators

What are electric radiator valves?

Two position control of steam or hot water to radiators and other heating coils. 

How does an electric radiator valve work?

Actuator has a small electric motor that opens the valve when the controller energizes the circuit and then a spring closes it. Can be manually opened if there is no power

What do solenoid operated valves operate?

They operate two position valves. Normally closed or normally open

What are modulating motors?

Electrical actuator used to position valves and dampers for process that require fully modulating FCE. Some will fail last when de-energized

What are stepper motors?

Brushless DC motor that rotates in steps instead of continuously. When a set of pole pieces are energized the rotor turns a certain amount and magnetically locks into position

What are advantages of stepper motors?

Speed is proportional to the frequency of the input pulses, max torque when at a standstill, precise, repeatable position of the rotor, rapid starting stopping and reversing, very slow speed operation and high reliability

What are disadvantages of stepper motors?

Low efficiency, drop in torque as speed increases, does not accelerate quickly under load, and difficult to operate at high rotational speeds

How does a furnace turn on?

If temperature is below set point, the thermostat switch closes and an electric signal is then sent to the furnace. Furnace starts and warms the air. When the temperature exceeds the set point the thermostat switch opens and burner shuts down

What does a transmitter do?

Converts measurements from a sensor into a signal and sends it to a remote recording device or controller

What type of signals can transmitters use?

Pneumatic (4-20 kpa), Electric (voltage or amperage), and Electronic

What does the spring do in a pneumatic transmitter?

Causes capsule to collapse as pressure is reduced

Valve capsule in pneumatic transmitter

Move up or down which opens or closes exhaust

Nozzle in pneumatic transmitter

Open port that bleeds air

Flapper in pneumatic transmitter

Connected to the process sensor through the link, it moves closer or further away from the nozzle

What is the output signal of pneumatic transmitters?

20-100 kpa

What is the feedback bellows in a pneumatic transmitter?

Reduced transmitter sensitivity that allows a definite distance between the flapper and nozzle, giving corresponding definite pneumatic output signal.

What happens if flapper moves away from nozzle if there is no feedback bellows in a pneumatic transmitter?

Pressure will go up, capsule will collapse if pressure lowers and spring acts against it, and feedback bellows reduces pressure causing it to pull the flapper slightly toward the nozzle giving a specific placement for an output signal

Differential transmitter

Similar to a pneuamtic transmitter but there is a low pressure side and a high pressure side which changes position of the flappers

Electric transmitters

Power supply provides voltage for the transmitter to make a 4-20 mA signal. Receives transmitter signal and converts back to voltage for controllers

Electronic transmitters

Electric signal converted to digital by a signal processor. Microprocessor takes signal and calculate the correct output of the new transmitter.

What is an indicator?

Give a visual reading of the process variable and provide no other function

What is a recorder?

Takes Process variable info and records it either electronically through trends or physically on a chart recorder and maintains a permanent record

Examples of pressure indicators are:

Bourdon tubes, bellows, pressure capsules

Examples of level indicators

Gauge glass and float. Pressure due to the static head presses on the diaphragm.

What is a circular chart recorder?

Spiral or helical bourdon tube connected to recording pens. Pressure on the bourdon tube is a pneumatic signal from a level, flow, or pressure. Full revolution in 24 hours or 7 days

What is a strip chart?

Moves in a linear fashion horizontally or vertically

Sensitivity in a pneumatic transmitter is fixed by adding a:

feedback bellows

Indicators are devices that can only be found in the field?

False

How does a controller work?

Brains of the control loop, compares process variable to the set point and if error is present it sends output signal to final control element to change the process

What is a modulating controller?

Anywhere from 0-100%

What is a non modulating controller?

Two positions, doesn’t change to any position. only what you have set

What are two position controllers?

On-off controllers. If error is present between PV and SP a contact (button or switch) will turn device on or off

What are multi position controllers?

Multiple contact closure outputs that operate in a sequence. Just adds more specific points to help with cycling

What are modulating controllers?

Produce infinitely variable control output signals based on error between PV and SP.

What are proportional controllers?

Compares size of error between PV and SP and sends out an OP signal in proportion to that difference.

What is error?

Set point - process variable