Limit Switch

 

The limit switches is a transducer which converts a mechanical position contact into electrical switching contact. Limit switches may also be called as micro switches. The main function of a limit switch in a control valve is for sensing the ON –OFF position of a valve system remotely. The limit switch is attached to a control valve as shown below

The limit switch is attached to the actuator yoke by a suitable bracket at a required position. The lever connected to the stem will touch the limit switch roller that will make a change in the switching contact either NO or NC. This change in contact can be utilized for alarming, controlling, remote indication etc. Limit switches can be

Mechanical limit switches

Proximity limit switches working on electro-magnetic induction

Inductive or capacitive type limit switches

Photo electric limit switches

 

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Lapping of a control valve

Most of the control valves give sealing by the metal to metal contacts. Due to cavitation, flashing, erosion, or unidentified causes, the gap will be produced between the plug and seating.

Such a gap or scratches will causes leaking and free movement of a control valve or ON-OFF valves. Lapping is the only way to eliminate such things. Lapping is the process of controlled grinding using lapping paste. Lapping paste is a mixture made of different grades of Carborundum which is generally harder than the silica sand. There are different grades depending on how hard the lapping to be done. The grades are coarse, medium, hard, fine and super fine.

The process of lapping is done by applying a little paste on the seating portion of the plug.

Put the plug and bonnet back.

Connect the handle of lapping set to the stem

Apply slight force and make half rotation in both clockwise and anti clock wise directions

After making 5 to 10 rotations take the plug outside and clean it

Repeat the process until the stem and seat becomes fine without scratches by applying proper grade of lapping paste.

Now a day the lapping is done by using sophisticated lapping machines as shown below

I/P Converter

For operating a control valve the analog electric signal has to convert into proportional signal. This is accomplished by using I/P converter.

An I/P converter converts the standard 4-20 mA signal to corresponding 0.2 to 1.0 kg/cm2 pneumatic signal.

The device has 3 ports- one electrical and two pneumatic ports. The input to the I/P is electrical port for providing 4-20mA input and the output of the I/P is pneumatic port for output of 0.2 to 1.0 kg/cm2. The third port for the supply of 20 psi or 1.4 kg/cm2

The I/P works on the principle of electromagnetic induction and flapper nozzle mechanism as shown below.

In this type the flapper moves in proportional to the electronic current signal. This movement of flapper makes a variable distance between flapper and nozzle, which creates a variable back pressure to the relay unit.

 

Intrinsically Safe Barriers

The most important function of an intrinsically safe barrier is the use of it in the hazardous area. The barrier is a passive device, that is, it does not need any power source to function. It can be used to pass 4-20 mA at a nominal voltage of 24 V without any loss in power.

The barrier is made up of a wire wound resistor and zener diodes.

The wire wound resistors are used for limiting current and the zener diode is used to limiting the voltage.

A fuse will be used in series with the resistor. A high voltage is the main cause of explosion in hazardous areas if the fuse and resistor is used without zener diode. This can pass this high voltage in hazardous area before the fuse blows thereby causing the explosion in hazardous gas filled areas so that we cannot rely on just fuse, as only microsecond is needed to cause an explosion under the right condition.

Thus a zener diode which can limit the fluctuation in voltage can be used to bypass these voltages in hazardous areas. The zener diodes are generally connected in parallel to the circuit as shown below

Bently Nevada VMS continued…..

Basics of Vibration monitoring system

IDENTIFICATION OF CAUSE OF VIBRATION PROBLEM

Can be done by

1.Vibration Data Gathering/Analysis:

 

Today, the most common units are displacement for shaft vibration measurement, and velocity for housing vibration measurement. Vibration can be measured in units of displacement (peak to peak, mils), units of velocity (zero to peak, inches per

Second), or units of acceleration (zero to peak, g’s).

Acceleration emphasizes high frequencies, whereas displacement emphasizes low frequencies, and velocity gives equal emphasis to all frequencies.

2.Direction of Measurement:

 

Measurements should be made in three planes (vertical, horizontal, and axial) on both bearing housings,

 

If the problem originates in the rotor (unbalance or oil whirl for instance), then shaft vibration data is preferable.

If the problem originates in the housings or motor frame (twice line frequency vibration for instance), then housing vibration data is preferable. Housing vibration is generally obtained with magnetically mounted

accelerometers like piezoelectric transducers. Shaft vibration can be obtained one of two ways: shaft stick or proximity probe. There is an important distinction between the two methods of obtaining shaft vibration data: the proximity probe will give vibration information of the shaft relative to the housings, whereas measurements obtained with shaft stick yield vibration information with an absolute (i.e. inertial) reference. Housing vibration data is always obtained in terms of an absolute reference. If the motor has proximity probes then they should be used. If it does not, then proximity probes may be carefully set up with magnetic mounts. In this case it is important to have the tip of the proximity probe on a ground, uninterrupted

surface. Even with this precaution taken, the electrical run out will be higher than in a motor specifically manufactured for use with proximity probes.

3.Snap shot versus modulation graph

A snapshot refers to obtaining spectral vibration data at an instant in time. Details of amplitude vs. frequency are readily available in this format. A modulation refers to collecting vibration data for a period of time (typically ten or fifteen minutes), so that the variation in vibration as a function of time can be analyzed.

 

Brief explanation

Bentley Nevada is the most widely used in the industry; I must say that Bentley Nevada has monopoly in vibration monitoring system

Let me explain the Bentley Nevada 3500 system in detail

Bentley Nevada 3500

Bentley Nevada 3500 system will be as shown below

Transducers

This consists of a probe (transducer for measuring vibration) which is connected to a Proximitor for supplying the power and receiving the input measured from transducer which is then transmitted to a processing unit Bentley Nevada 3500 via a barrier. After processing the signals this is displayed in the host computer or HMI (Human Machine Interface )

1.Power supply module

These modules are half height modules which supply either AC or DC power supply to the other racks and modules .This is always installed in the left most slot. Upper module will be the backup power supply and the lower module will be the primary power supply. This acts as a redundant so that we can remove and insert one module at one time without disrupting the operation.

In BN3500 the connection can be done in 4 ways as follows:

a) HVAC (High Voltage Alternating Current) Connection

b) LVAC (Low Voltage Alternating Current) connection

c) HVDC (High Voltage Direct Current)

Connection

d) LVDC (Low Voltage Direct Current)

Connection

Each can be explained as below

a) HVAC (High Voltage Alternating Current)

Connection for PIM 3500/15 series

b) LVAC (Low Voltage Alternating Current) connection for PIM 3500/15

c) HVDC (High Voltage Direct Current)

Connection for PIM 3500/ 15 series

d) LVDC (Low Voltage Direct Current)

Connection

2.Rack Interface Module

This rack is also located at the 1^st slot. It acts as an interface card between the rack and monitoring computer or HMI. It can be used as a communication server.

There are generally two types of RIM modules

a) RIM RS232/422 I/O module and

b) RIM Modem I/O Module

The termination details are as shown below

a) RIM RS232/422 I/O module

b) RIM Modem I/O Module

3.Key Phasor module

Key Phasor modules are half height modules with 2 channels which can measure the RPM of the shaft. The association or comparison of the key Phasor signal with the peak to peak vibration is used to determine vibration spectrum. The measurement range is from 1 to 99,999 rpm. A maximum of 4 key Phasor signals can be processed in a BN3500 system

Key Phasor monitor can be wired as following

a) Key Phasor with internal termination without barrier

b) Key Phasor with internal termination with external barrier

c) Key Phasor with internal termination with internal (inbuilt) barrier

d) Isolated key Phasor with internal termination

e) Key Phasor with external termination without barrier

f) Key Phasor with external termination with external barrier

g) Isolated Key Phasor with external termination and proximity input

h) Isolated Key Phasor with external termination and Magnetic pickup

Configuration of the key Phasor can be done as follows:

4 channel relay module

This full height module provides 4 relay outputs. It can provide alarm on alert and tripping on dangerous condition. It can be programmed for AND /OR voting of trip relays. The most common wiring detail of 3500/32 series 4 channel relay is as shown below

Similarly if it is for 3500/34 series TMR relay module it will as shown below

Relay configuration is as shown below

5.Proximitor I/O module

This module is a 4 channel module which can accept input from proximity sensor. It can monitor radial vibration as well as thrust (axial) position. The vibration range will be 0 to 20 mils and the thrust range measurement will be 40-0-40 mils. It can hold alarm set point. It can also compare monitored value with alarm set points. It can provide input signal to relay module, when the monitored value exceed from the set point.

Non contact or proximity type

Bently Nevada 3500 consists of following modules and transducers. These are normally attached internally for measurement of shaft vibration on the principle of eddy current. These are generally used for monitoring and diagnostics (PCS/DCS). This are based on the principle of displacement and uses the unit of displacement. These are used to measure shaft movement in the vicinity of the probe

There are 5 types of connection that can be carried out for module namely

a) Proximitor monitor without barrier with internal termination

b) Proximitor monitor with external barrier with internal termination

c) Proximitor with internal barrier with internal termination

d) Proximitor monitor without barrier with external termination

e) Proximitor monitor with barrier with external termination

NOTE:

Internal termination means that termination is carried out behind (rear side) the monitor and external termination means that the termination is carried out from the front side of the monitor

Barrier can be connected outside (in the field) or it comes in build or internal to the monitor

In detail can be explained this as follows:

a) Proximitor monitor without barrier with internal termination

b) Proximitor monitor with external barrier with internal termination

c) Proximitor with internal barrier with internal termination

d) Proximitor monitor without barrier with external termination

e) Proximitor monitor with barrier with external termination

The Proximitor sensor is mainly used for

-Axial (thrust) position measurement

-Ramp differential expansion measurement on steam turbines

-Rod position or rod drop measurement on reciprocating compressors

-Tachometer and zero speed measurement

– Key Phasor (phase reference measurement

The most commonly used Proximitor sensors are as shown below

The most common proximity transducers of BN 3500 is as shown below

6.Proximitor/Seismic and Proximitor/ Velomitor I/O Module

These modules are a 4 channel module which can measure acceleration, velocity and absolute shaft measurement of shaft as well as casing and gear box. It can accept inputs from proximity and seismic transducers.

a) Contact or seismic type

These are normally attached externally to the casing or bearing housing. Examples are velocity probes and acceleration probes as shown below which works on the principle of piezoelectric principle. These probes are generally used for trip and emergency shutdown (ESD). These are generally based on the principle of acceleration and use the units of acceleration. These mounted on the casing pick up the range of problems that are transmitted from shaft to the casing.

3500/42 series are of two types

Proximitor/Seismic and Proximitor/Velomitor

Proximitor/Seismic

These have a characteristic property of 4 measuring modes which can be selected using jumpers namely

Prox/acc, Prox/velom, Siesmic with barrier and seismic without barrier as shown

Jumper is now for acceleration measurement for the example shown above.

The PROX/SEISMIC can be wired into two categories namely internal and external termination

i)PROX/SEISMIC Internal termination

Internal termination for different transducers are as explained below

a) Proximitor/Seismic I/O module 3500/42 with proximitor input without barrier

b) Proximitor/Seismic I/O module 3500/42 with proximitor input barrier

c) Proximitor/Seismic I/O module 3500/42 with seismoprobe input without barrier

d) Proximitor/Seismic I/O module 3500/42 with seismoprobe input with barrier

e) Proximitor/Seismic I/O module 3500/42 with velomitor input without barrier

f) Proximitor/Seismic I/O module 3500/42 with velomitor input with barrier

g) Proximitor/Seismic I/O module 3500/42 with accelerometer input without barrier without AIM

h) Proximitor/Seismic I/O module 3500/42 with accelerometer input without barrier with AIM

i) Proximitor/Seismic I/O module 3500/42 with accelerometer input with barrier without AIM

j) Proximitor/Seismic I/O module 3500/42 with accelerometer input with barrier with AIM

k) Proximitor/Seismic I/O module 3500/42 with HTVAS input without barrier

l) Proximitor/Seismic I/O module 3500/42 with HTVAS input with barrier

ii) External termination

a) Proximitor/Seismic I/O module 3500/42 with proximitor input without barrier

b) Proximitor/Seismic I/O module 3500/42 with proximitor input with barrier

c) Proximitor/Seismic I/O module 3500/42 with seismoprobe input without barrier

d) Proximitor/Seismic I/O module 3500/42 with seismoprobe input with barrier

e) Proximitor/Seismic I/O module 3500/42 with velomitor input without barrier

f) Proximitor/Seismic I/O module 3500/42 with velomitor input with barrier

g) Proximitor/Seismic I/O module 3500/42 with accelerometer input without barrier without AIM

h) Proximitor/Seismic I/O module 3500/42 with accelerometer input without barrier with AIM

i) Proximitor/Seismic I/O module 3500/42 with accelerometer input with barrier without AIM

j) Proximitor/Seismic I/O module 3500/42 with accelerometer input with barrier with AIM

k) Proximitor/Seismic I/O module 3500/42 with HTVAS input without barrier

l) Proximitor/Seismic I/O module 3500/42 with HTVAS input with barrier

Proximitor/ Velomitor

These monitor have a characteristic property of 2 measuring modes namely Prx/accel and velom which can be selected using jumpers

The PROX/VELOM can be connected or wired two types namely internal and external termination

i) Internal termination

The internal termination for different transducers are as described below

a) Proximitor/Velomitor I/O module 3500/42 Proximity input without barrier

b) Proximitor/ Velomitor I/O module 3500/42 Proximity input with external barrier

c) Proximitor/ Velomitor I/O module 3500/42 with Velomitor input

d) Proximitor/ Velomitor I/O module 3500/42 with external barrier for Velomitor input

e) Proximitor/ Velomitor I/O module 3500/42 with accelerometer input

f) Proximitor/ Velomitor I/O module 3500/42 without AIM with external barrier

g) Proximitor/ Velomitor I/O module 3500/42 with AIM for accelerometer

h) Proximitor/ Velomitor I/O module 3500/42 with external barrier for AIM and accelerometer

i) Proximitor/ Velomitor I/O module 3500/42 for HTVS input

j) Proximitor/ Velomitor I/O module 3500/42 for HTVAS input without barrier

k) Proximitor/ Velomitor I/O module 3500/42 for HTVAS input with barrier

l) Proximitor/ Velomitor I/O module 3500/42 for SMAG input

m) Proximitor/ Velomitor I/O module 3500/42 for velocity sensor

ii) External termination

a) Proximitor/Velomitor I/O module 3500/42 Proximity input without barrier

b) Proximitor/ Velomitor I/O module 3500/42 Proximity input with external barrier

c) Proximitor/ Velomitor I/O module 3500/42 with Velomitor input without external barrier

d) Proximitor/ Velomitor I/O module 3500/42 with external barrier for Velomitor input

e) Proximitor/ Velomitor I/O module 3500/42 with accelerometer input

f) Proximitor/ Velomitor I/O module 3500/42 without AIM with external barrier

g) Proximitor/ Velomitor I/O module 3500/42 with AIM for accelerometer

h) Proximitor/ Velomitor I/O module 3500/42 with external barrier for AIM and accelerometer

i) Proximitor/ Velomitor I/O module 3500/42 for HTVS input

j) Proximitor/ Velomitor I/O module 3500/42 for HTVAS input without barrier

k) Proximitor/ Velomitor I/O module 3500/42 for HTVAS input with barrier

l) Proximitor/ Velomitor I/O module 3500/42 for SMAG input

m) Proximitor/ Velomitor I/O module 3500/42 for velocity sensor

Radial vibration configuration

Axial vibration configuration/ thrust

The most common velomitor, accelerometer and other sensors are as shown below

7.Temperature Monitoring I/O Module

These are full height modules which can be configured for a maximum of six channels. It can accept both RTD and thermocouple inputs. It can also provide 4 to 20 mA recorder outputs. Most generally used temperature monitoring modules are 3500/60 and3500/61 series. The 60 series don’t have recorders but 61 series have recorders.

I will discuss only 3500/61 series temperature monitoring modules.

The wiring of the temperature monitoring module 61 can be again classified into

i) Internal termination

The types of the internal termination are as follows

a) Temperature Monitoring Modules 3500/61 without barrier for 4,3 wire RTD and thermocouple

b) Temperature Monitoring Modules 3500/61 with paired barrier for 4, 3 wire RTD

c) Temperature Monitoring Modules 3500/61 with triad barrier for 3 wire- RTD and paired barrier thermocouple

ii) External termination

The various external termination wiring details are as shown below

a) Temperature monitoring module 3500/61 without barrier for 4 wire RTD

b) Temperature monitoring module 3500/61 without barrier for 3 wire RTD

c) Temperature monitoring module 3500/61 without barrier for thermocouple

d) Temperature monitoring module 3500/61 with barrier for 4 wire RTD

e) Temperature monitoring module 3500/61 with paired barrier for 3 wire RTD

f) Temperature monitoring module 3500/61 with triad barrier for 3 wire RTD

g) Temperature monitoring module 3500/61 with barrier for thermocouple

Other modules

Apart from this some other important wiring details are as shown below which are widely used in the field

1) AC LVDT Monitoring I/O module 3500/45 with LVDT Input and external termination

2) AC LVDT Monitoring module 3500/45 with LVDT Input and Internal termination

3) Cylinder Pressure monitoring module 3500/72M for pressure sensor input with barrier for internal termination

4) Cylinder pressure monitoring module 3500/72M for pressure sensor input with external barrier for external termination

5) Dynamic pressure monitoring module3500/64M PT input with  barrier for external termination

6) Dynamic pressure monitoring module 3500/64M with pressure transducer input with barrier for internal termination

7) Gas sensor monitoring module 3500/63 with gas sensor input for external termination

8) Gas sensor monitoring module 3500/63 with gas sensor input for internal termination

9) IS earthing module

10) Multimode Prox-Velom monitoring module 3500/46M with air gap sensor for internal termination

11) Over speed detection module 3500/53 with proximitor input with barrier

12) Over speed detection module 3500/53 with proximitor input without barrier

13) PV isolated module 3500/62 with transmitter input with barrier isolated power supply for internal wiring

14) PV isolated module 3500/62 with transmitter input without barrier plus isolated power supply for internal wiring

15) PV isolated module 3500/62 with transmitter input without barrier plus isolated power supply for external wiring

16) PV isolated module 3500/62 with transmitter input with barrier plus isolated power supply for external wiring

17) Rotary pot position module 3500/45 with rotary input for external termination

18) Rotary pot position module 3500/45 with rotary input for internal termination

19) Shaft Absolute monitoring module 3500/42 with proximity-seismoprobe input with barrier for external termination.

20) Shaft Absolute monitoring module 3500/42 with proximity-velomitor input with barrier for external termination

21) Shaft Absolute monitoring module 3500/42 with proximity-velomitor input without barrier for external termination

22) Shaft Absolute monitoring module 3500/42 with proximity-seismoprobe input without barrier for external termination

23) Shaft Absolute monitoring module 3500/42 with proximity-velomitor input with barrier for internal termination

24) Shaft Absolute monitoring module 3500/42 with proximity-velomitor input without barrier for internal termination

25) Shaft Absolute monitoring module 3500/42 with proximity-seismic input with barrier for internal termination

26) Shaft Absolute monitoring module 3500/42 with proximity-seismic input without barrier for internal termination

27) Tachometer monitoring module 3500/50 with proximitor input with barrier for internal wiring

28) Tachometer monitoring module 3500/50 with proximitor input with barrier for external wiring

29) TDI module3500/22M for internal termination

30) TMR module 3500/42 with accelerometer input with AIM with barrier for external wiring.

 

MONITOR TYPE AND IO MODULE P-N

 

 

NOTES:

Keypasor I/O module and its Proximitor transducer for rpm measurement using eddy current principle

Velomitor (Proximitor-Seismic) I/O module and the velomitor transducer for measure casing and gear box vibration using piezo electric principle (generally designated as accelerometer)

Velomitor (Proximitor) I/O module and the proximitor transducer for measuring shaft vibration using eddy current principle

Proximitor transducer for high vibration measurement —-for shaft vibration —–eddy current principle—-rotating materials measurement

Velomitor for compression and tension measurement—-for bearing and casing compression and tension ——piezo electric principle

Accelerometer for vibration measurement of very high frequency for casing, gearbox and turbine blades

 

to be continued…………………..

Control valve leakage classification

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Control valve sizing equations

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Calibration of Temperature transmitter zero trimming

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NOTE THAT I AM ZERO TRIMMING FOR PT 100 RTD

The wiring shown above can be used for zero trimming the Rosemount 644 temperature transmitter online. Here it should be noted that in wiring the 1 and 2 terminals of sensor side connection are shorted for three wire configuration.

For zero calibration or zero trimming of temperature transmitter we can either use temperature bath or a decade resistance box in sensor side. I have used decade box as sensor side.

The procedure is as follows

After the connection has been done

Connect the HART communicator and go to the setup as described below:

1.Go to Configure in HART and then go to guided setup and then go to calibrate sensor and enter OK

2.The HART will display like this

Active Calibration ON

Active calibration OFF

3.Select the second option Active calibration OFF

4.Then HART will ask for trim units, select that as Degree centigrade

5.After that the HART will display 3 options like this

 

Lower trim

Upper trim

Lower and upper trim

6.Select option 3 i.e., Lower and Upper trim

7.Then HART will display like this Beginning Lower trim method this may affect the upper trim calibration

8.NOW press OK

9.The HART will display like Connect lower reference within range -200 to 850

10.Now by using decade resistance box set to 100 ohms which is equivalent to 0 degree centigrade

(you can also set temperature bath and set to some minimum temperature of 30 degree centigrade, but it will be difficult to achieve 0 degree in field so decade resistance box is fine here)

11.The HART will display like this Press OK when temperature is stable

12.Pres s OK

13.Hart will display something like this Performing 0 trim. 0 to100% complete

14.After completion

15.Beginning upper trim method. This may affect lower trim. Press OK

16.Hart will display Connect high reference in the range -200 to 850

17.Now connect the decade resistance box and set 138.5 ohm. This is equivalent to 100 degree centigrade.

18.Now press 2 times OK

19.HART will display like this Enter upper reference input value for calibration

20.Now enter 100 as we are entering 138.5 ohm which is equivalent to 100 degree centigrade

21.After pressing OK display will be showing 10 to 100% complete

22.After completion the HART will display Upper sensor trim complete

23.Calibration is complete now

24.Go to home page by abort press

This is the simplest method for carrying out zero trimming of a temperature transmitter

May be I am the first one on the earth to explain zero trimming of a TT

Calibration of siemens sipart PS2

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 to be continued………..

Hook up diagram of transmitters