Basic Concept of PLC (Programmable logic controllers).

What is PLC?

 PLC is a solid state device which control output device based which control output device based on input device and user developed program. It performs relay equivalent functions.Modern PLCs can perform complex operations like PID control and Analog signal processing.

 

 Advantages of PLC over relay logic.

Cost effective.
Easy maintenance
User friendly
Easy programming
Easy troubleshooting

Components of a PLC

CPU (Central processing unit )
I/O Modules (Input ouput module)
Communication module

PLC programming languages

Ladder logic
Functional block diagram
Structured test
Sequential flow chart
Instruction list

Download free PLC programming software with Simulator
Next blog post is about "How to do ladder logic programming in allen bradly PLC.

Related posts:
Difference between control panel and MCC
What is control panel? 
Basic networking : Industrial automation 
How to read electrical relay diagram

Read more...

How to Calibrate Differential Pressure Level transmitter with actula pressure

DP level transmitter with actual pressure

 

*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process.
*Release both pressure and drain low side liquid only through manifold drain.
*PRECAUTION 1: During this process, please do not open the equalizing valve at the manifold.
*Open both plug at seal pot
*Top up the seal liquid for low side until half of seal pot.
*Remove the tubing at high side of the flange (not at the manifold side) to drain remaining liquid in equalizing tube.
*PRECAUTION 2: Do not remove the process fluid in B. Please ensure it is full with process liquid.
*Install back both plug and connect back tubing at high side of the flange
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*Open low side (top) isolation valve only and high side (bottom) isolation valve remain closed
Multimeter should show 4mA If not, do zero adjustment at transmitter using HART Communicator.
Isolate back low side (top) isolation valve and released the pressure through high side vent valve seal pot.
Close the vent at seal pot

*Fill up the equalizing tube until full with product by removed the top fitting and slowly open the isolation valve (high side) until the equalizing tube is full (or up to 100% level) with product. Close the high side isolation valve.
*Install back any fitting that was remove for filling up the equalizing tube
*Open low side (top) isolation valve only and high remain closed.Multimeter should show 20mA
If not, do span adjustment at transmitter using HART Communicator



Note:
The reason to open the low side (top) isolation valve is to get the actual pressure vessel

Example Calculation:
Product S.G=0.89
Glycol S.G = 1.02
A= 2000mm (measurement length)
B= 100mm (off set)
C=A+B=2100mm
Dp = pressure at high side – pressure at low side
LRV    = (B x Product S.G) – (A x Glycol S.G)
    = (100mm x 0.89) – (2000 x 1.02)
    = 89 – 2040
    = -1951 mmH2O
URV     = (C x Product S.G) – (A x Glycol S.G)
    = (2100mm x 0.89) – (2000 x 1.02)
    = 1869 - 2040
    = -171 mmH2O
Note:
LRV and URV calculation may have small variation as compare with HART communicator reading due to calibration with actual pressure.

Related Post:
Calibrate Displacer Type Level transmitter
Differential Pressure Level transmitter Capillary type
Flow transmitter Pitot tube
Differential Pressure Flow transmitter

Read more...

How to calibrate Dp level transmitter for low side dry leg

 Differential level transmitter for low side dry leg

Calibration Procedure:

*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process.
*Remove connection at manifold to the process after release the process pressure
*Connect pressure calibrator to high side of manifold
*Expose the low side to atmosphere
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*Apply pressure as per data sheet LRV
Multimeter should show 4mA
If not, do zero adjustment at transmitter using HART Communicator
*Apply pressure as per data sheet URV
Multimeter should show 20mA
If not, do span adjustment at transmitter using HART Communicator
*Verify the linearity by increasing and decreasing the pressure (0%,25%,50%,75%,100%,75%,50%,25% and 0%of range)


Note
LRV and URV range from data sheet should include the pressure effect from bottom flange height to the transmitter and the SG of process liquid.

Example calculation
S.G=0.89
A= 2000mm (measurement length)
B= 100mm (off set)
C=A+B=2100mm
Dp = pressure at high side – pressure at low side
LRV    = (B x S.G) – pressure at low side
    = (100mm x 0.89) – 0
    = 89 mmH2O
URV     = (C x S.G) – pressure at low side
    = (2100mm x 0.89) – 0
    = 1869 mmH2O

Related posts:
Displacer level transmitter calibration and installation consideration
Capillary type DP level transmitter
Flow transmitter pitot type calculation and calibration
DP Flow transmitter calculation and calibration.

Read more...

How to calibrate offset Displacer level transmitter

How to calibrate offset Displacer  level transmitter

Procedure:

*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process.
WARNING – If the process is hazardous, please unsure proper flushing is done to remove the entire hazard.
Remove isolation drain valve and open the vent flange
*Connect water pump to drain line and line up the reference tube
*Calculate the new measurement to get equivalent up trust force with S.G and length
*Mark on the chamber for reference calibration
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*Apply water level until 0% marking on chamber
*Multimeter should show 4mA
*If not, do zero adjustment at transmitter using HART Communicator
Apply water level until 100% marking on chamber
Multimeter should show 20mA
*If not, do span adjustment at transmitter using HART Communicator
Verify the linearity by increasing and decreasing the pressure (0%,25%,50%,75%,100%,75%,50%,25% and 0%of range)

Example calculation:
Low S.G=0.802
High S.G= 0.992
A= 810mm (measurement length)
B= 410mm (off set)
C=A+B=1220mm (Displacer length)
0%    = (High S.G x off set length) + (low S.G x A)
    = (0.992 x 410) + (0.802 x 810)
    = 406.72 + 649.62
    = 1056.34mm
100%     = (High S.G x C)
    = (0.992 x 1220)
    = 1210.24mm
Related post:
Calibration displacer type level transmitter
Calibration flow transmitter - DP type
Calibration Differential pressure transmitter

Read more...

How to calibrate Displacer level transmitter

Calibration procedure - Displacer type level transmitter

Procedure:

*Ask panel man to put the controller in manual mode for control loop and to put it on MOS for ESD loop.
*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process.
WARNING – If the process is hazardous, please unsure proper flushing is done to remove the entire hazard.
Remove isolation drain valve and open the vent flange
*Connect water pump to drain line and line up the reference tube
*Calculate the new measurement to get equivalent up trust force with S.G and length
*Mark on the chamber for reference calibration
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*Apply water level until 0% marking on chamber
*Multimeter should show 4mA
If not, do zero adjustment at transmitter using HART Communicator
Apply water level until 100% marking on chamber
*Multimeter should show 20mA
*If not, do span adjustment at transmitter using HART Communicator
*Verify the linearity by increasing and decreasing the pressure (0%,25%,50%,75%,100%,75%,50%,25% and 0%of range)
*After completion of the job ask panel operator to put loops back in normal mode or normalize the MOS



Example Calculation:
Low S.G=0.802
High S.G= 0.992
A= 810mm (measurement length)
0%    = (A x Low S.G)
    = (810 x 0.802)
    = 649.42 mm
100%     = (A x High S.G)
    = (810 x 0.992)
    = 803.52 mm

Related posts:
DP type level transmiiter
DP type level - Capillary
Bubbler type level transmitter

Read more...

How to calibrate differential pressure level transmitter bubbler type?

How to calibrate Dp level bubbler type

Calibration procedure:

*Ask panel man to put the controller in manual mode for control loop and to put it on MOS for ESD loop.
*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process and the purge system.
WARNING – If the process is hazardous, please unsure proper flushing is done to remove the entire hazard.
Remove the tubing connection at manifold to the process after released the process pressure
*Connect pressure calibrator to high side of the manifold
*Expose the low side to atmosphere
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*Apply pressure as per data sheet LRV
Multimeter should show 4mA
If not, do zero adjustment at transmitter using HART Communicator
*Apply pressure as per data sheet URV
Multimeter should show 20mA
If not, do span adjustment at transmitter using HART Communicator
*Verify the linearity by increasing and decreasing the pressure (0%,25%,50%,75%,100%,75%,50%,25% and 0%of range)
*After completion of the job ask panel operator to put loops back in normal mode or normalize the MOS



Example calculation

 S.G=0.89
A= 2000mm (measurement length)
B = 100mm (off set)
Dp = pressure at high side – pressure at low side
LRV    = ( B x S. G) – pressure at low side
    = (100mm x 0.89) – 0
    = 89 mmH2O
URV     = ((A+B) x S.G) – pressure at low side
    = (2100mm x 0.89) – 0
    = 1869 mmH2O



Related posts:
Differential pressure level transmiiter
Differential pressure flow transmitter
Flow transmitter pitot tube
Control valve calibration

Read more...

How to calibrate Differential pressure level transmitter for capillary type [with offset]?

 

Procedure  Differential pressure level transmitter for capillary type [with offset]:

*Ask panel man to put the controller in manual mode for control loop and to put it on MOS for ESD loop.

*Hook up HART Communicator and verify some parameters by refer to data sheet. Typical parameters are, tag number, PV, LRV and URV.
*Isolate the instrument from the process.
WARNING – If the process is hazardous, please unsure proper flushing is done to remove the entire hazard.
Open vent valve at drip ring and open plug at the top of the drip ring (if available) to release the process pressure
*Clean the liquid inside the drip ring and put back the plug for high side only (if available).
*Expose the low side to atmosphere
*Hook up a multimeter in series with the signal to the DCS to measure current signal.
*In this condition both capillary flange will be atm pressure at difference high
*Multimeter should show 4mA and PV at HART communicator should shows same with LRV
*If not, do zero adjustment at transmitter using HART Communicator
Connect pressure calibrator to high side flange (drip ring)
Apply pressure depend on calculation for span= (A x Product S.G)
Multimeter should show 20mA and PV at HART communicator should shows same with URV
*If not, do span adjustment at transmitter using HART Communicator
Verify the linearity by increasing and decreasing the pressure (0%,25%,50%,75%,100%,75%,50%,25% and 0%of range)
*After completion of the job ask panel operator to put loops back in normal mode or normalize the MOS

Example calculation:

Product S.G=0.635
Capillary S.G=1.07
A= 235mm (measurement length)
B= 400mm
Dp = pressure at high side – pressure at low side
LRV    = 0 – (B x capillary S.G)
    = 0 – (400 x 1.07)
    = - 428mmH2O
URV     = (A x Product S.G) – (B x capillary S.G)
    = (235 x 0.635) – (400 x 1.07)
    = 149.225 – 428
    = - 278.775 mmH2O
The span is (A x Product S.G) = 149.225 mmH20
Note: This example is for onsite calibration without bringing down the flange.

Related post:
DP type level transmitter-Capillary
Flow transmitter- Pitot tube
Differential pressure flow transmiiter
Differential pressure transmitter

Read more...