automated controls

This is the user set, desired output

Set point

This is the actual reading given from a sensor, and the condition being controlled

Process variable

This is what the system changes to influence the process variable

the specific factor or parameter that the control system changes in order to maintain the process at the desired setpoint.

Manipulated variable

The sensor (like a thermocouple, pressure transducer, or flow meter) that detects the initial change in the process variable.

Primary element

This is what makes decisions or the brains

Controller

This is what reads the variable process

Sensor

Converts the controller's signal (electrical, pneumatic, or hydraulic) into physical, mechanical force or motion. The muscle

Actuator

The entire physical device that directly interacts with and alters the fluid, air, or process variable. The executer

Final control element

This is what the controller is trying to change

Process

This is what is sent back to the controller, which was read by the sensors

Feedback

When the controller opposes change and moves system back to set point

Negative feedback

When the system reinforces change away from the set point

Positive feedback

This is a control system that switches either on or off, like a light switch

Discontinuous control

When control system adjusts with a range, like a dimmer

Continuous control

Describe what the following letters mean as the first letter in a P&ID tag.

P F T M L

Pressure, Flow, Temperature, Motor, Level

What does P&ID stand for?

Piping and instrumentation diagram

What does K and D mean?

K = Gain (how much)

D = Dynamic response (how fast)

If a control loop has no feedback what would it be called?

Open loop

If a loop has feedback what would you call it?

Closed loop

If the process variable increases and the output increases what would that be called?

Direct acting

If the process variable increases and the output decreases what would you call that?

Reverse acting

On a P&ID tag, what does a circle represent?

Discrete instrument

On a P&ID tag, what does a square represent?

Shared display or monitor

On a P&ID tag, what does a hexagon represent?

Computer function

On a P&ID tag, what does a square with a diamond inside represent?

PLC

On a P&ID tag, what does one line represent?

Accessible operator primary

On a P&ID tag, what does two line represent?

Accessible operator secondary

On a P&ID tag, what does a dashed or dotted line represent?

Inaccessible

On a P&ID tag, what does no line represent?

Located in the field

On a P&ID tag, what does these second letters represent?

T I V D C R

Transmitter, Indicator, Valve, Differential Controller, Recorder

On a graph what does an analog output wave look like?

Straight and smooth

For a digital output what would it look like on a graph?

Like stairs, pulses on and off

What does this line represent

Pneumatic

What does this line represent?

Electrical

What does this line represent?

Hydraulic

What does this line represent?

Guided electromagnetic

What does this line represent

Unguided electromagnetic

This type of system corrects itself based on the size of the current error, bigger error means a bigger correction

Proportional

This type of system corrects itself based on the accumulation of past errors over time

Integral

This type of system corrects itself based on the rate of changes of the error, predicts future trends

Derivative

What is the difference between a sensor and a transducer and transmitter

A sensor detects.

A transducer changes one type of energy to another.

A transmitter takes info from a transducer and translates it into usable information for a PC, PLC or controller.

What part of a controller reads the sensor input and makes a decision based on the set point

Comparator

This is the difference between the set point and the process variable

Error

What is the main difference between an input transducer and an output transducer

Input transducer - reports what's happening

Output transducer - makes something happen

What is a common output in milliamps, PSI and voltage?

4-20 mA

3-15 psi

1 to 5 volts

What do we call our two wire loop when it is set at 4 to 20 milliamps?

Live zero

How is a 2 wire, live zero loop beneficial?

What are the down sides?

It is good for long runs, 0 millivolts indicates a fault instead of just being off, simple, easy to verify and troubleshoot.

Carries both power and signal on same conductor.

One fault makes the whole system go down, needs correct polarity, needs shielding.

Can you name the seven different object detectors?

Photoelectric, Limit switch , Pneumatic, Magnetic, Inductive proximity, Capacitive proximity, Ultrasonic

Which type of object detector can sense the most diverse amount of objects

Capacitive.

Which object detector uses sound and listens for an Echo?

Ultrasonic

Which object detector can be mounted flush or non-flesh and can only detect metal by sending out energy which gets absorbed?

How do the flush and non-flush sensors differ?

Inductive

Flush has a narrow sensor area and is recessed.

Non-flush has a wider sensor area.

Which object detector has a hall switch and a reed switch

How do the two differ?

Magnetic.

Reed switch is single state uses electronics.

All switch has moving parts with a magnet and can wear out much faster.

What do we use to convert 4 to 20 milliamps to 1 to 5 volts?

250 ohm resistor

Red Green Brown

What type of object detector physically touches the objects to sense them?

What precaution do we take with this type?

Limit switch.

Must not be used as a mechanical stop.

What type of object detector shoots air from a nozzle and detects back pressure.

Where is this type of object detector good for?

Pneumatic.

Good for heavily soiled, dusty or hazardous areas.

What type of object detector uses a beam of light?

What are the three different beams called and how do they work?

Photoelectric.

1 Through beam sensor - laser shines from emitter through to a receiver on other side

2 retro reflective - beam shines from emitter and reflects from a mirror back to the receiver on the same device

3 diffuser reflective - laser is reflected back to receiver from the actual object that intercepts the laser.

What is the difference between light on and dark on

Light on - output turns on when it sees light

Light off - I'll put it turns on when it does not see light

With input transducers, what is the difference between active and passive?

Active creates its own electrical signal, like a thermocouple, creating electricity from heat.

Passive needs external excitation to change energy types, or an external supply for power. Like an RTD or thermosister.

What type of controller has the fastest control time?

PID controller

(Proportional integral derivative)

The number in the P&ID symbol indicates the..

Loop where the instrument is located

In a P&ID tag, what do the letters following the first letter generally identify?

Instrument function

What does RVDT stand for?

Rotary variable differential transformer

I'm an RVDT, when set to the null position, what is the output voltage?

0 volts. Both equal secondary voltages cancel each other out.

What does LVDT stand for?

Linear voltage differential transformer

This motion sensor has two secondary coils wound around a hollow tube. A core provides path for flux lines to pass from primary to secondary

LVDT

What are the three types of motion sensors

Linear displacement

Angular position

Rotary speed

This type of motion sensor measures distance and direction in a straight line

Linear displacement

This type of motion sensor measures rotation angle in degrees or rad

Angular position

This motion sensor senses rotation speed in RPM

Rotary speed

With a linear variable inductor, when the core moves further into the shaft what happens

More inductance.

What's it hey Tachogenerator, how does DC and AC differ?

DC forwards and backwards

AC one way only

With an incremental encoder what happens when you lose power

You lose your spot and need to reset

With an absolute encoder what happens when you lose power

You don't lose your spot!

With the two different kinds of encoders, one circle has notches and the other looks like a dart board. Which is which?

Notches = incremental

Dart board = absolute

On a incremental encoder, what does lights A&B do? What does Z do?

A & B Measures movement speed

Z is null. Each Z pulse is a full rotation

How do you determine the amount of positions in an absolute encoder

2 to the power of how many bits the encoder is

When a strain gauge is compressed what does resistance do?

What about when there's tension?

Compression Goes down

Tension goes up

What does a loop powered transmitter do?

Uses loop power and regulates current according to the measurement

Can you name the six methods of temperature sensing?

RTD

Thermistor

Thermocouple

Bymetallic sensor

Fluid filled

Radiant pyrometer

How does an RTD detect temperature

Resistance increases

How does a thermistor detect temperature

Resistance changes sharply

How does a thermocouple detect temperature

Creates millivolts in DC

How does a bimetallic sensor detect temperature

Produces movement with two dissimilar types of metal

How does the fluid filled sensor detect temperature

Produces pressure

How does a radiant pyrometer detect temperature

By detecting radiant energy

What does RTD stand for?

Resistance temperature detector

What are the different ways an RTD is wired?

What is the most popular?

Which is the most accurate?

Two wire, three wire and four wire.

Four wire is the most accurate

3-wire is the most popular

What is a thermistor typically used for?

Over temperature protection. Very sensitive

What is a RTD typically used for?

Accuracy and measurement.

What types of thermocouple are the most common and why?

What are the two types used for?

J and K. More predictable.

K furnaces (wide range)

J ovens (lower temperature range)

What are the positives and negatives of a thermocouple

Rugged, fast acting, high temperature,

Not accurate.

Which one of these graphs is from which?

RTD, thermocouple, thermistor

How does a bimetallic sensor work? What is the downside?

Two different metals expand at different rates

Slow to respond, less accurate

What are the two parts in a fluid-filled sensor?

Capillary tube and bourdon tube

What is the metal pocket called that protects the sensor from the process

Thermo well

What makes a radiation pyrometry unique

Other sensors require physical immersion, pyrometry does not.

What temperature sensor is the best for hazardous locations

Radiation pyrometry.

Can sense from a distance

Hydrostatic pressure can determine the level of open tank, sealed tank or both?

Open

A conductive probe makes what kind of measurements?

Point. Can only measure once liquid level is high enough to cover contacts and create continuity.

What is deadband

The range of values that a process variable can fluctuate without triggering any adjustments