ecet 211 electric machines & controls relays -...
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ECET 211 Electric Machines & Controls
Relays
Text Book: Electric Motors and Control Systems, by Frank D. Petruzella, published by McGraw Hill, 2015.
Paul I-Hai Lin, Professor
Electrical and Computer Engineering TechnologyP.E. States of Indiana & California
Dept. of Computer, Electrical and Information Technology
Purdue University Fort Wayne Campus
Prof. Paul Lin
Lecture 7 Relays
Part 1. Electromechanical Control Relays
• Relay Operations
• Relay Applications
• Relay Styles and Specifications
Part 2. Solid State Relays
• Operation
• Specifications
• Switching Methods
Part 3. Timing Relays
• Motor-Driven Timers
• Dashpot Timers
• Solid-State Timing Relays
• Timing Functions Prof. Paul Lin 2
Part 4. Latching Relays
• Mechanical Latching Relays
• Magnetic Latching Relays
• Latching Relay Application
• Alternating Relays
Part 5. Relay Control Logic
• Control Circuit Inputs and Outputs
• AND Logic Function
• OR Logic Function
• Combinational Logic Functions
• Not Logic Function
• NAND Logic Function
• NOR Logic Function
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Part 1. Electromechanical Control RelaysRelay Operations
Electromagnetic Relay – a switch that is operated by an electromagnet
Two parts of Electromechanical Control Relay (Figure 7-1):
• Coil input (control circuit)
• Contacts output (Load circuit)
Used to control small load of 15A or less
Applications
• Control coils in motor contactors and starters
• Switching solenoids, pilot lights, audible alarm, and small motor (1/8 hp or less)
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Part 1. Electromechanical Control RelaysRelay Operations
Figure 7-2 Relay coil and contacts
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Typical Relay Applications: One relay controls multiple pilot lights
Figure 7-3 Relay coil and contacts – CR1, CR2
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Part 1. Electromechanical Control RelaysRelay Applications
Current or signal amplification (small signal current => control large load current)
Control high-voltage load: 12 V => 480V load
Figure 7-4 Relay used to control a high-voltage
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Control high-current load
Figure 7-5 Using a relay to control a high-current load circuit with a low-current control circuit
• Relay: coil and contact
• Solenoid (2 A, 120V)
• Electronic parts: Diode, Transistor, Resistor (limit current)
Part 1. Electromechanical Control Relays
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Theory of Operation – Figure 7-5 Control High Current Load
Relay coil - on/off control by a power Transistor switch
Relay switching on/off induced high Spike voltage e = - L ∆i/∆t
Transistor: • Three terminal device: Collector,
Emitter, Base
• Base input current 2 mA, Collector output current 20mA: a gain of 10
Diode (fast on/off switch)–protecting transistor: fly wheeling diode turned-on, when VA – VK ≥ 0.7 V
Solenoid value current 2 A
• Total Current Gain = 2A/2mA = 1000
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Part 1. Electromechanical Control RelaysRelay Styles and Specifications
Figure 7-6 Plug-in style ice cube relay
Figure 7-7 Relay manual push-to-test button
Figure 7-8 Typical DIN-rail with relays mounted
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Part 1. Electromechanical Control RelaysRelay Styles and Specifications
Figure 7-9 Common relay contact switching arrangement
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Part 2. Solid State RelaysOperation
Solid-State Relay (SSR)
• An electronic switch contains no moving parts
• Does not have coils and contacts
• Use semiconductor switching devices: Bipolar transistor, MOSFET, SCR, Triac
Figure 7-10 Typical solid-state relay
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Part 2. Solid State Relays
Operation
Figure 7-11 Optically coupled SSR used for AC load
Figure 7-12 Optically coupled SSR used for DC loads
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Part 2. Solid State RelaysSpecifications
Input voltage range: 5V DC to 24V DC, 32 V DC
Output voltage range: 5V DC up to 480V AC
Current rating: < 10A, up to 40 A, 50A (heat sink required)
Figure 7-13 Multiple-pole SSR connections
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Part 2. Solid State RelaysSpecifications
Figure 7-13 Three-wire control utilizing a SSR and an SCR
SCR (Silicon Control Rectifier)
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Part 2. Solid State RelaysSwitching Methods
Zero-switching relay (Zero crossing)
Peak-switching relay
Instant-on relay
Thermal dissipation
Leakage current
Cost
Figure 7-15 Zero Crossing SSR
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Part 2. Solid State RelaysSwitching Methods
Figure 7-16 SSR heat sink
Loads more than 5A require a heat sink for reliable operation
Figure 7-17 Electromechanical vs. SSR construction
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Part 3. Timing RelaysTiming Relays – An Introduction
A time actuated control relay in which a fixed or adjustable time occurs after a change in the control signal before switching action occur.
Enable a multitude of operation in a control circuit to be automatically started or stopped at different time intervals
Figure 7-18 Timing relays
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Part 3. Timing RelaysMotor-Driven Timers
Figure 7-19 Synchronous clock timer
Dashpot Timer
Figure 7-20 Dashpot (Pneumatic) Timers
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Part 3. Timing RelaysSolid-State Timing Relays
Figure 7-21 Solid-state timing relay connections
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Part 3. Timing RelaysSolid-State Timing Relays
Timing Functions
On-Delay Timer
• Figure 7-22 On-delay timer contacts
Off-Delay Timer
One-Shot Timer
Recycle Timer
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Part 3. Timing RelaysTiming Functions – On delay timer
Figure 7-23 On-delay timer circuit
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Part 3. Timing RelaysTiming Functions - Off-Delay Timer
Figure 7-24 Off-delay timer
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Part 3. Timing RelaysTiming Functions – Off Delay Timer
Figure 7-25 Off-delay timer automatic pumping circuit
Water level rises to point A => Level sensor contact on => Energize Off-delay timer => Turns on the pump to initiate the pumping action
Water level decreases => Level sensor contact open => Timing begin => The pump Continue to run and empty the tank for the length of the delay time
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Part 3. Timing RelaysTiming Functions - One-Shot Timer
Figure 7-26 One-shot timer
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Part 3. Timing RelaysTiming Functions - Recycle Timer
Figure 7-27 Recycle timers
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Part 3. Timing RelaysMultifunction Timer – a timer that perform more than one timing function
Figure 7-28 Multifunction digital timer
H5CX-N, 0.001 s to 9999 h,http://industrial.omron.us/en/products/catalogue/control_components/timers/digital_timers/default.html
PLC Timers
Most common types of PLC timer instructions
• On-delay timer (TON)
• Off-delay timer (TOF)
• Retentive Timer On (RTO)
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Part 3. Timing RelaysFigure 7-29 PLC programmed on-delay timer
Hardware wire
• Pressure Sw => I3 (input)
• Pilot Light => Q1 (Output)
Enter Ladder diagram using keypad and LCD display
PLC Program Execution
• Pressure SW on => energize Timing coil T1 => Initiating the time-delay period
• After 5 sec have passes, T1 (NO contact) closed to energize relay coil Q1 and turn on the pilot light
• Open Pressure SW, resets the time value to zero
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Part 4. Latching RelaysLatching Relays – use a mechanical latch or permanent magnet to hold the contacts in their last energized position.
Mechanical Latching Relays
Figure 7-30 Two coil mechanical latching relay
Figure 7-31 Operation of a two-coil latching relay circuit
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Part 4. Latching RelaysMagnetic Latching Relays
Polarity sensitive
Relay is latched when the applied voltage with a predetermined polarity.
• A permanent magnet is used to hold the relay in its latched position.
A voltage polarity is reverses =>
unlatch the relay
Figure 7-32 Single-coil magnetic latching relay
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Part 4. Latching RelaysLatching Relay Application
For those applications that need to conserve the power, such as a battery-operated device
Figure 7-33 Battery-operated latching alarm circuit
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Part 4. Latching RelaysAlternating Relay (Impulse Relays)
It transfers the contacts with each pulse.
For special applications where the optimization of load usage is required by equalizing the run time of two loads.
Figure 7-34 Alternating or pulse relay
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Part 4. Latching RelaysAlternating Relay (Impulse Relays): Pumping Application
Two identical pumps are used for the same job.
• One for normal running
• One for backup
Running Methods
1) A standby unit is made available in case the first pump fail. However, a completely idle pump might deteriorate and provide no safety margin.
2) Both pumps get equal run time, alternately
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Part 4. Latching RelaysAlternating Relay (Impulse Relays): Pumping Application
Figure 7-35 Typical alternating relay circuit used with a duplex pumping system
• Use an Alternating Relay to ensure that both pumps get equal run time.
• In the off state, the Float SW is open, the Alternating relay is in the Load A position; both Loads (M1 and M2) are off.
• When the Float SW closes, it energizes the first load (M1) and PL1.
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Part 4. Latching RelaysAlternating Relay (Impulse Relays)
Figure 7-36 DPDT cross-wired contact version of a dual pumping application
Alternate Mode
• Normal Level
Lead and lag Flow SWs close simultaneously => Pumps A and B on (for heavy flow)
Only one pump is operating most of the time; yet the system has the capacity to handle twice the load
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Part 5. Relay Control Logic
Control Circuit Inputs and Outputs
Figure 7-37 Typical inputs and outputs of a control ladder diagram
• Input section
• Output section
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Boolean Algebra
Also see - Digital Logic (pages 257-258)
Boolean Logic
Logic AND
Logic OR
Logic NOT
Truth Table
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AND OperationM Coil ON = STOP (closed) AND START (ON)ORM Coil ON = STOP (closed) AND M Auxiliary Contact Closed
STOP START
M
V+ V-
CoilM Auxiliary
Contact
OR OperationM Coil ON = SATRT (ON) OR M Auxiliary Contact Closed
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Boolean Algebra – Logic AND
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V-
AND OperationM = A AND B
A B
M
V+
Coil
V-
AND OperationM = A AND B
A B
M
V+
Coil
A B M0 0 0 0 1 01 0 01 1 1
Truth TableInputs Output
Boolean EquationM = AB
Boolean Algebra – Logic OR
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Boolean Algebra – Logic NOT
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A
M
V+
Coil
V-
A
Standard Digital NOT Gate
M
A M0 1 1 0
Boolean EquationM = NOT A
Truth TableInputs Output
Boolean Equation
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A B C F
0 0 0 00 0 1 10 1 0 00 1 1 11 0 0 01 0 1 11 1 0 11 1 1 1
Truth TableInputs Output
Boolean EquationF = (AB) + CF = (A AND B) OR C
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Part 5. Relay Control Logic
AND Logic Function
Figure 7-38 AND logic function
OR Logic Function
Figure 7-39 OR logic function
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Part 5. Relay Control Logic
Combinational Logic Functions
Figure 7-40 AND/OR combinational logic
Both (On/Off switch AND Limit switch) must be ON AND (Sensor contact or PB be ON) => Contactor coil ON
Not Logic Function
Figure 7-41 Not logic function
Use to prevent accidental contact with live electrical connections.
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Part 5. Relay Control Logic
NAND Logic Function
Figure 7-42 NAND logic function
For dual-tank liquid filing operation
NAND = NOT (FS-1 OFF AND FS-2 OFF) => Pump starter coil (OFF) => Pump Motor shut down
NOR Logic Function
Figure 7-43 NOR logic function
NOR = NOT (Stop-1 OFF, Stop-2 OFF, Stop-3 OFF)
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Summary & Conclusion
Questions?Contact Prof. Lin through:
Email: [email protected]
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