Automated Controls Flashcards
An washing machine is a closed loop system? True/False
False
Name the four “Basic Elements” of a closed loop system.
- Measurement Sensor
- Controller and Error Detector
- Final Control Element
- The Process
Name several alternative names for “Measurement Sensor” in a control system.
-Sensor
-Detector
-Transducer
Transmitter
Provide a few examples of open loop systems.
-Washing machine
-Toaster
-Dishwasher
They use the process of time, not measurement of outcome.
What does ISA stand for in the discipline of Automation Control?
ISA = International Society of Automation
Provide a few examples of closed loop systems?
- Water heater
- furnace with thermostat
- Natural Gas pressure regulator in the home.
What is the purpose of a P&ID Diagram?
To provide an basic schematic of the process.
What is the purpose of the block diagram?
To show the system as a set of mathematical equations that describe input to output relationship for each individual block. This allows for the evaluation of the total control system before it’s implemented.
What is negative feedback in Automated Controls?
Is measured by comparing set-point and actual result. IE like a flame in a variable furnace. As heat gets close to setpoint it reduces gas supply, then finally turns it off.
What is positive feedback in Automated Controls?
Does the opposite thing than what is desired. IE turning furnace flame higher as it gets closer to set-point. Causing runaway condition.
The “Transfer Function” of control system component primarily relates to?
The size and timing of the input to the output.
What does “Controller Action” select?
Chooses positive or negative feedback control
A device that receives info in one from and converts it to antoher form is called?
Transducer
A device that receives info in one from and converts it to another form is called?
Transducer
What is a type of transducer that includes a sensor and components to standardize and modify the sensors output?
Transmitter
What is difference between active and passive transducer?
Active gets energy from the energy output of the things it’s measuring IE Thermocouple. Passive requires power from the transducer to measure. IE Weight scale resistance sensor needs power supply to measure resistance change due to weight.
What are the two standards for measuring Voltage and current?
Current 4mA to 20mA
Voltage 1-5 Volts DC
Why use a 250 Ohm resister in control systems?
It converts 4mA to 20mA signal to 1-5 VDC signal for such devices as data loggers and alarms.
Why use current signal instead of voltage transmission?
Current has less interference over long distances without losses. It allows for a 2 wire system where power supply can be located a distance away.
Provide 2 examples of disadvantages of using current signal system.
All equipment must be connected in series.
Open loop if one thing disconnects.
What is Hysteresis in Automated Controls?
A device give an upscale or downscale error depending on which way the thing is being measured. This is usually because of slack of friction in the system.
Is a Bias Error the same as a Zero Error?
Yes. This is when Acutual output = Theoretical output
A “Span error” in a measuring device is an indication of incorrect “Gain.” True/False
True.
A “Variable Gain Error” in a measuirng device is also know as a ______ error?
Linearity
What is the term for inconsistency of a transducer performance?
Repeatability
What is a smart transmitter?
A device which can communicate both ways. And can be re-configured.
What is disadvantage of Smart, remote controlled system?
Likely to be hacked
What is continuous control
Analogue
What is discontinuous?
Digital
What are things we can measure?
- pressure
- temperature
- flow
- level
- light
- colour
- distance
- speed
- position
- gas
- weight
- PH
What does a sensor do? What are several of these things?
- Respond to an input.
- insensitivity to other mediums
- should not influence the change in what’s is being measured.
- accurate
- without error
- proportional change in output with respect to input
What is the primary element in relation to a sensor?
What is being measured.
What are examples of electrical sensor?
- Photoeye
- proximity switch
- RTD
- thermistor
- thermocouple
- ultrasonic
- strain gauge
What is RTD?
Resistive temperature detector
Does a transducer include a transmitter?
Yes, as well as amplifier and filter.
What are examples of electrical signals? Up to 6 things.
4-20 mA 0-10V Frequency Resistive Capacitances Inductance
What is a passive transducer?
Requires a power supply
What is a active transducer?
No power supply required
When it comes to current sensing a what is range and span?
Range 4-20mA
Span is 16mA
What is accuracy in relation to a sensor?
The limit within which the output may deviate.
What is the linearity error?
The output is above and below the theoretical straight line.
What is repeatability in relation to a sensor?
The ability of a device to have a consistent output with consistent input conditions.
What does Bourdon tube do when pressure is increases?
Tube straightens out.
What does Bellow measure and what does it do?
Pressure. It expands out like an accordion. Linearly. Differential in pressure.
What does a diaphragm measure?
Pressure.
A diaphragm puts a signal of capacitance. How does this work?
One metal movable plate on diaphragm. Other metal plate stationary. A change in distance between the pates alters the capacitance.
What does the conditioner(transmitter) do?
- Filters
- AmplifyH
- Receives the electrical signal from the sensor.
A diaphragm is hooked to a coil. How does it sense changes?
Inductance changes as core or transformer moves between primary and secondary coils.
Man-o—meter uses what to operate? How does it work?
Uses pressure.
Forces process pressure on a sealed tank. This forces liquid in a tube. Which you can read.
When measuring pressure we measure it always against something else. What is the most common one?
Atmospheric pressure
A variable area meter. What is it? How does it work? What does it measure?
- A water flow meter. Manual sight meter.
- A float in a V shaped goes up or down depending on flow rate
- Measures Liquid flow. Generally water.
How does a turbine flow meter work? What does it measure?
- A turbine in a pipe spins when water flows past
- measures flow
How does a magnetic flow meter work?
- Flow of conductive liquid moves between electrodes.
- current is generated the faster the flow.
How does channel flow meter work?
Uses Weir. Rate of flow changes distance of water falling over edge through weir.
What are ways to measure temperature non-electrically?
Pressure IE with bourdon
Volume
Shape IE bi-metallic strip
What are ways to measure temperature electrically?
- Thermocouple (active sensor)🔺voltage
- RTD thermistor 🔺resistance
- change in colour (optical pyrometer)
Which one has a positive temp increase?
Thermocouple
RTD thermistor
RTD has positive temp co-efficient.
What does positive temp co-efficient mean?
As temp goes up resistance goes up. Semi-conductors are like this.
How does a strain gauge work?
Uses 🔺 resistance. Increase pressure reduce resistance.
What is the process variable in a residential hot water tank?
Water temperature
In a residential HWT was is:
Manipulated variable?
Controlled variable?
Feedback type?
Manipulated variable: Gas
Controlled variable: water temp
Feedback type: negative
When filling a propane tank what pressure is it?
- Absolute
- atmosphere
- gauge?
Gauge
How does a Hall effect sensor work?
It senses current flow by sensing a voltage at 90 degrees to the conductor
What is final control element in a HWT?
The burner
What is the Dead band? 💀
The dead area between the lower and upper set-point. When nothing happens.
What is steady state?
When output and input match. IE when a water tank is being filled at the same rate as it’s being emptied.
What is gain?
The change in output based on the change in input.
What is the Capacitance of a process?
The ratio of the total capacity to rate of outflow.
Y=mx + b in control technology is?
Y = Kc * e * y
Y= controller output signal Kc= proportional gain constant E= set point measured variable y= controller initial condition
If the range is -100C to +100C what is the span?
200C
What is proportional gain?
Output changes proportionaly to the input
What is Proportional plus Integral gain (reset)?
Output changes relative to how long the error has been present. (Time) So the longer the problem the stronger it tries to solve it.
What is derivative gain?
It takes into consideration the rate or change of the error.
A sensor has an input of 20-60 PSI and output of 4-20mA. What input pressure will cause an output of 6.2mA?
25.5 PSI
A sensor has an input of 0-180 Litres/min, and an output of 0-10V, when connected to a PLC (8 bit register.) 50L/minute is flowing.
- what is input voltage
- what is the decimal value stores in the register?
- what is the binary value stored in the register?
-2.778V
71
01000110
What does a servo motor do?
A servo motor moves and provide feedback on how it moved.
What are the two kinds of water/chemical valves when it comes to how it’s opened and closed.
Linear motion
Rotary motion
Servo motors are only DC motors. True/False?
False. Can be either AC or DC
What are the three forms of a servo motor commutation device (feedback?)
- incremental encoder
- absolute encoder
- resolver
What does an Incremental encoder give feedback on?
Speed feedback
What does an Absolute encoder give feedback on?
Positional feedback
What does an Resolver encoder give feedback on?
Used for position
How does a resolver encoder work?
Uses sine and cosine coils to detect position. Controller looks at outputs from coils and know.
How does a stepper motor work?
There is no feedback. Energizes only a couple coils in the motor so shaft only moves a small (step) amount. It’s build like a 3 phase motor. But runs very different.
What is atmospheric pressure measured at sea level?
14.7 PSI
Keep in mind atmospheric pressure varies slightly based on the weather.
What is absolute pressure?
A pressure measured from zero.
What is what is gauge pressure?
It is the pressure above atmospheric pressure, the difference from that.
Is atmospheric pressure a variable or constant?
It is a variable as air pressure outside varies with the weather. Think of a high-pressure or low-pressure system being predicted.
What is the difference in pressure between two points called? How is it expressed?
Differential pressure or Delta P or 🔺P
What is an inferential measurement?
The difference in pressure between two points. Usually before and after an orifice. Is measured and converted into units of flow rate. This is an example of an inferential measurement, where changes in different pressure units infer a change in flow rate.
What is hydrostatic pressure?
It is the weight of a fluid at the bottom of the tank. Sometimes called head pressure, hydrostatic head.
How does a variable resistance pressure sensor work?
The bellows move a potentiometer to change the resistance value.
How does a variable capacitance pressure sensor work?
A pressure plate moves a capacitor plate back-and-forth thereby increasing or reducing the capacitance.
How does a variable inductance pressure transducer work??
The displacement of the diaphragm changes the position of the iron core inserted inside the coil, thereby changing the magnetic coupling between the primary and secondary coil. This uses AC power.
What does a differential pressure cell or DP cell do?
This utilizes two diaphragm pressure sensors the electronics in the transmitter subtract the reading from the low pressure side and the reading on the high-pressure side and provides a output from the two. An example is a liquid tank with a sealed top. As the level drains a vacuum is created above the waterline and you need to use to pressure sensors to figure out how much is in there.
How does a Manometer work?
This is a visual site gauge. It is a pressure difference measurement. It consists of tube of glass or clear plastic which is filled with a water. One end of the tube is open to the atmosphere, the other end of the tube is connected to a closed tank with liquid in it. Pressure connected to the tank will force water up the tube indicating the pressure in the tank.
Name three different types of mechanical primary elements commonly used in deflection type pressure sensors.
Bourdon tube
Bellows
Diaphragm
What is the common purpose of the secondary element in a pressure sensor?
To convert the primary element movement into a proportional electrical change that can be used for display or signal purposes.
What is the purpose of the signal conditioner?
The signal conditioner is used to take the secondary element conversion to resistance, capacitance or inductance change and produce a useable or standard signal.
What is the common name of the pressure sensor that subtract the reading on the lower side from the reading on the high side?
A differential pressure sensor
If the specific gravity of one fluid is higher than another, is it heavier?
Yes
What are four ways closed loop final element can be controlled?
ON/OFF Control o Proportional o Proportional Integral o Proportional Integral Derivative
What Controlled environments are the best applications for ON/OFF Controls?
Large Capacity, slow changing process variables
In Proportional Controlled Systems the TOTAL LOOP GAIN is a calculation of what three elements?
Transmitter + Controller + Final Control Element = Total Loop Gain
Which type of Control ensures the removal of steady state?
Proportional Integral Derivative
Derivative Control responds to the Control System in what way?
Reducing Response time
If the comparison of the values between the Sensor feedback and the Set Point results in the addition of those two values – what is this condition called and what will be the resulting actions of this system?
Positive Feedback – resulting in runaway
In a Water Reservoir using float switches to start and stop a pump motors what is the Process Variable?
Level of the water
What does P&ID stand for?
Piping and Instrumentation Diagrams
Flow can be determined by measuring the______ ____of the pressure drop across a restriction in the flow path
Square root
