timer indutrial automation
DESCRIPTION
industrial automationTRANSCRIPT
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Industrial Mechatronics Lecture # 6
Hammad Nazeer Office: B Block, Blue Faculty Room
Email: [email protected]
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Timers
Mainly used for providing delays in between sequences & operations
There are 4 different types of Timers:
– Off Delay Timers
– On Delay Timers
– Retentive On timers
– Retentive Off timers
Examples of Usage:
– Consider a garage light which should remain ON for 2 minutes before turning off.
Non Retentive
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Off Delay Timers
The timer turns ‘ON’ as soon as the input turns high
Starts incrementing when the input has turned false and turns ‘OFF’ when a certain time has been achieved
Examples:
– A garage light which should remain ON for 2 minutes before turning off.
– Consider a car whose ignition key has been turned off but the car engine remain ‘ON’ for some time
– Cooling fans remain “ON” for some time after the oven has been turned off
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ON Delay Timers
Starts incrementing when the input has becomes true and turns ‘ON’ when a certain time has been achieved
It turns OFF immediately as the input turns OFF.
Examples:
– Consider a car whose ignition key has been turned ON but the car engine turns ON after some delay
– An On delay timer would allow an oven to reach a specific temperature before starting production
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Retentive Timers
• Retentive timers:
– They don’t lose their accumulated values once the enable input lines go low
– They retain the accumulated value until the enable input lines goes high again
– They function like stop watches. They can start and stop and retain their current values until a reset button is pressed
• Non Retentive timers:
– The timer value goes to Zero once the enable input goes low
– Thus non retentive timers lose the accumulated value
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Basic Similarities in Timers
• There are some basic common aspects in a Timer blocks made by different PLC vendors:
– Timers will have a number to identify them (for example T7 in case of Rockwell)
– Time Base:
• Timers can be programmed with different time basis, for example 1 second, 0.1 second and 0.01 second
• Example:
– If a timer has 0.1 second time base and the user entered 50 as the number of delay increments then delay would be 5 seconds
– Preset Value:
• The preset value is the number of increments the timer has to count before it changes it output. 50 is the preset value in the previous case
– Accumulated Value:
• It refers to the current increment the timer has reached during its operation
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Rockwell Timers
• On Delay Timer: – It starts accumulating when the rung
becomes true and continues until the
preset value becomes equal to the accumulated value or the rung goes false
– Basic Symbol used is T and the file number is 4 (T4).
• Status Bits Usage: – Enable Bit (EN): It turns on immediately when the rung goes true and
remains set until the rung goes false or timer is reset
– Timing Bit (TT): It remains true when the rung goes true or accumulated value is less then preset value
– Done Bit (DN): It is set when the accumulated value equals the preset value
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Example of On Delay Timer
• The preset value is 4000ms, so delay of 4 seconds. • The preset value is 4000ms, so delay of 4 seconds.
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Addressing Special Bits
RsLogix 500 RsLogix 5000
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Rockwell Timers
• Off Delay Timer: – It starts accumulating when the rung
becomes False and continues until the
preset value becomes equal to the accumulated value or the rung goes True
• Status Bits Usage: – Enable Bit (EN): It turns on immediately when the rung goes true and
remains set until the rung goes false or timer is reset
– Timing Bit (TT): It remains true when the rung goes False and accumulated value is less then preset value
– Done Bit (DN): It is set when rung becomes true and reset when accumulated value is equal to preset value
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Example of Off Delay Timer
• The preset value is 3500ms, so delay of 3.5 seconds.
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Retentive ON timer
• Similar to ON timer except that it retains its value.
• The preset value is 4000ms, so delay of 4 seconds
• How can we use the timer after the cycle has completed?
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Example
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Example
• Consider the scenario in which a start button turns on the Heater
and the Stop button (normally closed) turns it off. Initially there is a
delay of 10 sec before the heater turns ‘ON’. After the heater is
turned ‘OFF’ the cooling fans remain ON for 5 minutes
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Cascaded Timers
• The timers are connected to each other and thus are called
cascaded timers
• Each timer drives the other timer
• Mainly used when a single timer can’t provide the delay
required
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Timers of other PLC Vendors
• GE FANUC TIMERS & CONTACTS:
• There are of the following basic types:
• ONDTR (On delay timer) Retentive timer
• OFDT (Off delay timer) Retentive timer
• TMR (On delay timer) Non retentive timer
• Contact addressing in GE FANUC:
• %I represents inputs %I0005 represents real input 5
• %Q represents outputs %Q0003 represents real output 3
• %R represents system registers
• %AI Analog Inputs
• %AQ Analog Outputs
ONDTR
TB
Time
Base R
PV
%R0001
Enable Input Output ONDTR
TB
R
PV
%R0001
Enable Input Output
Time
Base
ONDTR
TB
R
PV
%R0001
Enable Input Output ONDTR
TB
R
PV
%R0001
Enable Input ONDTR
TB
R
PV
%R0001
Enable Input ONDTR
TB
R
PV
%R0001
Enable Input Output
Time
Base
ONDTR
TB
R
PV
%R0001
Enable Input ONDTR
TB
R
PV
%R0001
Enable Input ONDTR
TB
R
PV
%R0001
Enable Input Output
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Timers of other PLC Vendors • Gould Modicon Timers & Contacts:
• The figure shows a Non retentive Gould
Modicon Timer.
• The delay can be calculated by multiplying the
preset value with the time base
• The Timer has two outputs, one which operates when the timer
accumulated value equals the preset value and the other output is
inverted
• Contact Addressing:
• 0 at the start represents outputs 0005 represents the 5th real
output
• 1 at the start represents inputs 1002 represents the 2nd real input
• 4 at the start represents Storage registers example 4004
Reset
Preset Value
Time Base
Storage Register
Enable Output
Output
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Solve
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Solve
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Counters
• Counters are used in many important industrial applications
• Mainly used in Production lines where the items have to be counted
• When we are counting the number of products we might use a count up timer
• When we are counting the number of parts left we might use a count down timer
• The choice of counter to be used depends on the application
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Operation of Counter
• There are different types of counters:
– Count up
– Count down
• They use a low to high transition for counting action
• Timers count time increments whereas counters count pulses on input lines
• Timer increments its value with each low to high transition and turns ‘ON’ when the accumulated value equals the preset value
• Counters are edge triggered devices and don’t accumulate when the level is remain high (level triggered)
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Rockwell Automation Counters
• Rockwell Automation Counters – Use the filer number 5 for counters and the symbol C
– So counter values would be stored in C5:0
– Counters are retentive and a reset bit must be used to return the accumulated value to zero
• Counters have the following essential elements: – CU (Count Up bit)
– CD (Count Down bit)
– DN (Done bit)
– OV (Overflow bit)
– UN (Underflow bit)
– PRE (Preset value)
– ACC (Accumulated value)
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Count Up Timers
• Count Up Timers (Retentive): – The accumulator (ACC) value increases
with every low to high transition
– The done bit (DN) is set when the accumulated value equals the preset value
– The over flow bit (OV) turns on when the counter value increases by 32,767. It then wraps around and starts counting from -32,768 (this is how 16 bit signed numbers are stored)
– The count up (CU) shows that the Counter has been enabled (it turns on when ever the rung condition goes true)
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Example of Count Up Counter
• Contact B is used to Reset the counter
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Example
• A count up (CU) Counter is used to remove the 6th Part of
every 11 parts that are detected and then resets the
counters
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Count Down Counter
• Count Down Timers (Retentive): – The accumulator (ACC) value decreases
with every low to high transition
– The done bit (DN) is set when the accumulated value equals or greater then the preset value
– The over flow bit (OV) turns on when the counter value decreases by -32,768. It then wraps around and starts counting from 32,767
– The count down (CD) shows that the Counter has been enabled (it turns on when ever the rung condition goes true)
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Example of Counters
• Count Up & Count Down Counters can have the same
registers
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Cascading Counters
• What is happening here?
• When will the last counter done bit (DN) be set?
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What is the output?
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Counters from Other Vendors
• GE FANUC TIMERS:
• There are of the following basic types:
• UPCTR (Up counter) Retentive Counter
• DNCTR (Down Counter) Retentive Counter
• UPCTR:
• Every time the input turns “High” it increments the Counter value
by ‘1’ and if it is equal to the preset value, the counter turn ‘ON’
• The ‘R’ input is used to reset the counter
• DNCTR:
• Every time the input turns “High” it decrements the Counter value
by ‘1’ and if it is equal to the preset value, the counter turn ‘ON’
• The ‘R’ input is used to reset the counter
ONDTR
TB
R
PV
%R0001
Enable Input ONDTR
TB
R
PV
%R0001
Enable Input UPCTR
R
PV
%R0001
Enable Input Output
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• Gould MODICON Counters:
– When the input pin transitions from
Low to high the counter increments the
Counter value
– The reset pin must be high for the counter to
Count
– The output value goes high when the input value equals the preset value
– The counter also provides an inverted output
Counters from Other Vendors
Reset
Preset Value
CTR
Storage Register
Enable Output
Output
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Solve