signal
Components of the control loop communicate with each other via standard signal, either pneumatic or electronic. Process information such as pressure, flow, temperature and level are converted to standard signals through instrumentation. The standard electrical signals are sent to the control system ( DCS ) through signal cable.
The signal cable are going through the following path :
1. Sensor to converter / transmitter ( single pair cable or special cable )
2. Converter / Transmitter to junction box single pair instrument cable )
3. Junction box to DCS Marshalling cabinet ( multicore cable )
As an example, consider a standard level control loop on 5 meters high tank of water consisting of an electronic differential pressure transmitter, a controller and a linear control valve using 4-20 mA signals. Assume a level is at steady state with the tanks at a level of 2 meters and a valve opening at 42%. Signal around the loop would be calculated as follows :
Transmiter output = ( 2 mtr /5 mtr ) x (20 mA-4mA) + 4 mA
= 10,4 mA
Controller output = ( 42%/100%0 x (20 mA-4 mA) + 4 mA
= 10,72 mA
Note : this example uses a standard output signal 4-20 mA, cause every company has a different standard. Maybe 0-20 mA, 0-10 V, or in pneumatic uses 3-15 psi.
DCS and Related Part
Distributed Control System ( DCS ) has a bundle of a part with related together in a rack room, electrical room, and a control room.
2. Basic DCS I/O electronic
2.1 Electronic Review
In electronic system, it is necesarry to be familiar with some basic terms. There are current, voltage, resistance, and impedance.
Current is a flow of electronic in a wire. this flow is usually considered to be from negative end to positive end. Sometime, the opposite of electron flow is used to define current. In order for electron to flow, a pressure or force must be applied to make them move. this is called voltage and it is measured in volts. The higher the voltage, the greater the force applied to the electronics. If a current is open for any reason, such as a switch or breaker wire, then the current will not flow. Voltage might still be present, the effective resistance of the circuit is so high that the power supply can not push any electron through it, so current stops.
Every device in use in a electric circuit has a resistance to the force of voltage.This will also tend to restrict the flow of electron through the device. The relationship between voltage, current and resistance is V = IxR. Impedance is a type of resistance found in AC circuit. Since our DCS using field I/O is DC, impedance is not discussed.
2.2 Fusing and Circuit Protection
Fusing is used to protect power supplies from short circuit and other electro-mechanical faults. Short circuits are condition in which the total circuit resistance is dropped to zero. This will cause the power supply to generate an infinite currrent, resulting in severe damage to the output components of the power supply.
A fuse is a special piece of wire,enclosed in a glass tube, designed to pass a fixed amount of current. if the current exceeds the designed amounts,the wire will melt, opening the circuit and preventing any voltage or current from passing.
2.3 Relay
Relays are electro-mechanical devices that are used to switch current off and on only. They are consists of an electronic coil and one or more sets of mechanical switches called contacts. The contancts are held inplace by spring. the type of contact can be either normally open or normally closed, this depending upon the state they are in when the relay is sitting on a shelf and not connected to anything.
The relay operates on the basis that a voltage, when applied to the electric coil, will cause the coil to develop a magnetic field ( this is called energized ). The magnetic field overcomes the force of the spring and will cause the contacts to change state. In this way, it operates as a switch and can open and close circuits under direction from a processor. When the coil is de-energized, the spring holding the contacs will cause the switches to return to their normal state.
3. DCS Part
In general, DCS has 3 important part with connecting together to carry on/back data to the field. They are :
1. Controller/control processing unit
2. Cross Connection cabinet
3. Operator Station
3.1 Controller
Inside this cabinet, it has a controller as a brain of process control. Controller in this case called AC450( Advant Controller ) includes :
a. CPU with memory ( system software and application software )
b. Submodules carrier SC510 or SC520
c. Voltage Regulator SR511
d. Backup Power Supply SB510
e. Supervisory module TC520
f. LAN module CS513
g. Program Card Inteface MB510
3.2 Cross Connection Cabinet
I/O modules are set up on cross connection cabinet which include end of external wiring from field and also internal wiring connected to each module terminal. The I/O modules consist of theree basic components :
1. Connection Unit
Different types of connecton unit used are S100 and S800. In my pulp mill uses S800 and in power mill uses S100. S800 Connection Unit has :
1. TU830 for AI810, AO810, and DI810
2. TU831 for DO820
2. Board Modules
- S800 Board Modules
- AI810 for analog input signal
- AO810 for analog output signal
- DI810 for digital input signal
- DO820 for digital output signal
3. Cable
Connection from controller C1520 to S800 I/O CI810VI has 2 kid of connection :
- TK515 cable, used to connect from CI520 to TC512
- Fiber Optic, used to connect from CI520 to TC514
3.3 Operator Station
The operator station called human machine interface is an interface between the oprator and controller. All process information from controllers is presented on the operator station. The controller via operator station also carries out the operator command. Operator station is connected to the MB300 (Mater bus 300) via RTA board (back of operator station ). The stream of information controller using CS513 on the controller, use AUI cable (TK575) through tranceiver.
4. Software Application
The ABB DCS software application or process application consist of 2 parts :
1. Database (DB)
Every single connection unit like S800 will have its own database in the controller. The data base for I/Os corresponds to their type of I/Os are :
- AI database element for the analog input I/O
AI = analog input ( signal fro field )
- AO database element for the analog output I/O
AO = analog output ( signal from DCS )
- DI database element for the digital input I/O
DI = digital input ( contact at field )
- DO database element for the digital output I/O
DO - digital output ( power 24vdc to field )
2. PC program
The PC program are the process control application programmed in ABB Master Programming Language (AMPL). It is a function block language with graohics representation which has been developed especially for process control application.The smallest unit of the language is called PC element. A fully functional control loop consist of several PC elemnets and the input and output of the element are connected to the input and outputs of other elements or from/to process I/O point.
3. List Of Drawing
List of drawing which could explain what is interlock, what's the properties included its database, alarm settins, list of alarm, and also software which is installed ON ABB system.
The signal cable are going through the following path :
1. Sensor to converter / transmitter ( single pair cable or special cable )
2. Converter / Transmitter to junction box single pair instrument cable )
3. Junction box to DCS Marshalling cabinet ( multicore cable )
As an example, consider a standard level control loop on 5 meters high tank of water consisting of an electronic differential pressure transmitter, a controller and a linear control valve using 4-20 mA signals. Assume a level is at steady state with the tanks at a level of 2 meters and a valve opening at 42%. Signal around the loop would be calculated as follows :
Transmiter output = ( 2 mtr /5 mtr ) x (20 mA-4mA) + 4 mA
= 10,4 mA
Controller output = ( 42%/100%0 x (20 mA-4 mA) + 4 mA
= 10,72 mA
Note : this example uses a standard output signal 4-20 mA, cause every company has a different standard. Maybe 0-20 mA, 0-10 V, or in pneumatic uses 3-15 psi.
DCS and Related Part
Distributed Control System ( DCS ) has a bundle of a part with related together in a rack room, electrical room, and a control room.
2. Basic DCS I/O electronic
2.1 Electronic Review
In electronic system, it is necesarry to be familiar with some basic terms. There are current, voltage, resistance, and impedance.
Current is a flow of electronic in a wire. this flow is usually considered to be from negative end to positive end. Sometime, the opposite of electron flow is used to define current. In order for electron to flow, a pressure or force must be applied to make them move. this is called voltage and it is measured in volts. The higher the voltage, the greater the force applied to the electronics. If a current is open for any reason, such as a switch or breaker wire, then the current will not flow. Voltage might still be present, the effective resistance of the circuit is so high that the power supply can not push any electron through it, so current stops.
Every device in use in a electric circuit has a resistance to the force of voltage.This will also tend to restrict the flow of electron through the device. The relationship between voltage, current and resistance is V = IxR. Impedance is a type of resistance found in AC circuit. Since our DCS using field I/O is DC, impedance is not discussed.
2.2 Fusing and Circuit Protection
Fusing is used to protect power supplies from short circuit and other electro-mechanical faults. Short circuits are condition in which the total circuit resistance is dropped to zero. This will cause the power supply to generate an infinite currrent, resulting in severe damage to the output components of the power supply.
A fuse is a special piece of wire,enclosed in a glass tube, designed to pass a fixed amount of current. if the current exceeds the designed amounts,the wire will melt, opening the circuit and preventing any voltage or current from passing.
2.3 Relay
Relays are electro-mechanical devices that are used to switch current off and on only. They are consists of an electronic coil and one or more sets of mechanical switches called contacts. The contancts are held inplace by spring. the type of contact can be either normally open or normally closed, this depending upon the state they are in when the relay is sitting on a shelf and not connected to anything.
The relay operates on the basis that a voltage, when applied to the electric coil, will cause the coil to develop a magnetic field ( this is called energized ). The magnetic field overcomes the force of the spring and will cause the contacts to change state. In this way, it operates as a switch and can open and close circuits under direction from a processor. When the coil is de-energized, the spring holding the contacs will cause the switches to return to their normal state.
3. DCS Part
In general, DCS has 3 important part with connecting together to carry on/back data to the field. They are :
1. Controller/control processing unit
2. Cross Connection cabinet
3. Operator Station
3.1 Controller
Inside this cabinet, it has a controller as a brain of process control. Controller in this case called AC450( Advant Controller ) includes :
a. CPU with memory ( system software and application software )
b. Submodules carrier SC510 or SC520
c. Voltage Regulator SR511
d. Backup Power Supply SB510
e. Supervisory module TC520
f. LAN module CS513
g. Program Card Inteface MB510
3.2 Cross Connection Cabinet
I/O modules are set up on cross connection cabinet which include end of external wiring from field and also internal wiring connected to each module terminal. The I/O modules consist of theree basic components :
1. Connection Unit
Different types of connecton unit used are S100 and S800. In my pulp mill uses S800 and in power mill uses S100. S800 Connection Unit has :
1. TU830 for AI810, AO810, and DI810
2. TU831 for DO820
2. Board Modules
- S800 Board Modules
- AI810 for analog input signal
- AO810 for analog output signal
- DI810 for digital input signal
- DO820 for digital output signal
3. Cable
Connection from controller C1520 to S800 I/O CI810VI has 2 kid of connection :
- TK515 cable, used to connect from CI520 to TC512
- Fiber Optic, used to connect from CI520 to TC514
3.3 Operator Station
The operator station called human machine interface is an interface between the oprator and controller. All process information from controllers is presented on the operator station. The controller via operator station also carries out the operator command. Operator station is connected to the MB300 (Mater bus 300) via RTA board (back of operator station ). The stream of information controller using CS513 on the controller, use AUI cable (TK575) through tranceiver.
4. Software Application
The ABB DCS software application or process application consist of 2 parts :
1. Database (DB)
Every single connection unit like S800 will have its own database in the controller. The data base for I/Os corresponds to their type of I/Os are :
- AI database element for the analog input I/O
AI = analog input ( signal fro field )
- AO database element for the analog output I/O
AO = analog output ( signal from DCS )
- DI database element for the digital input I/O
DI = digital input ( contact at field )
- DO database element for the digital output I/O
DO - digital output ( power 24vdc to field )
2. PC program
The PC program are the process control application programmed in ABB Master Programming Language (AMPL). It is a function block language with graohics representation which has been developed especially for process control application.The smallest unit of the language is called PC element. A fully functional control loop consist of several PC elemnets and the input and output of the element are connected to the input and outputs of other elements or from/to process I/O point.
3. List Of Drawing
List of drawing which could explain what is interlock, what's the properties included its database, alarm settins, list of alarm, and also software which is installed ON ABB system.
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