About kishore karuppaswamy

Iam Btech having experience in saudi aramco as instrument engineer

HART Communication

Characteristics of HART

HART-Highway Addressable Remote Transducer

HART is a digital industrial Automation Protocol or Communication Protocol.

A HART device is a microprocessor-based process transmitter which supports a two-way communication with the Host.

HART digital signal is modulated onto the 4-20 mA analog signal at a higher frequency and is observed by the process control equipment

For any communication protocol explanation we have to consider OSI (Open System Interconnection) model of ISO, this gives us a general architecture of network specification,

OSI model has 7 layers








HART uses layer 1 layer 2 layer 4 and layer 7 and if wireless uses an additional layer 3

Layer 1 Physical layer

Layer 1 Physical layer

Data transmission between masters and field devices is physically realized by superimposing an encoded digital signal on the 4–20 mA current loop.

The physical layer defines an asynchronous half-duplex interface that operates on the analog current signal line. To encode the bits, the FSK method, based on the Bell 202 communication standard, is used. Digital value 0 is assigned frequency 2200 Hz, and digital value 1 is assigned frequency 1200 Hz.

HART masters are connected in parallel to the field devices.

HART wiring in the field usually consists of twisted pair cables.

The network technology used is

a) Either FSK for HART versions 1, 2,3,4,5

The HART Communication Protocol is based on the Bell 202 telephone communication standard and operates using the frequency shift keying (FSK) principle. The digital signal is made up of two frequencies: 1,200 Hz and 2,200 Hz representing bits 1 and 0, respectively. Sine waves of these two frequencies are superimposed on the direct current (dc) analog signal cables to provide simultaneous analog and digital communications


b) PSK for HART 6 and 7 versions

PSK Physical Layer—a higher speed physical layer option—is available in the HART 6 and HART 7 versions of the HART Protocol. PSK supports significantly faster communications with standard command/response throughput of up to 10-12 transactions per second simultaneous with the 4-20mA signal.

c) TDMA for wireless HART

A Wireless HART network utilizes Time Division Multiple Access (TDMA) technology to ensure that only one instrument is talking on a channel at any given time. This prevents message collisions within the Wireless HART network. A network is provided with an overall schedule which is divided into 10 ms timeslots. At any time, only one pair of instruments are communicating on the same frequency channel, however, it is possible that more than one pair of instruments can communicate at the same time using different channels. In most cases, only one pair of instruments is communicating in a given timeslot so the Wireless HART network will not monopolize the frequency spectrum that is shared with other wireless networks.

In HART individual bus devices can communicate via the topology specified below.

The physical layer can be of 5 types. This means that the network configuration used are

i)Point-to-Point Network

point to point

In point-to-point mode, the 4-20mA signal is used to communicate one process variable, while additional process variables, configuration parameters, and other device data are transferred digitally using the HART Protocol. The 4-20mA analog signal is not affected by the HART signal and can be used for control. The HART Communication digital signal gives access to secondary variables and other data that can be used for operations, commissioning, maintenance and diagnostic purposes

ii)Multi-drop Network

multi drop

The multi-drop mode of operation requires only a single pair of wires and, if applicable, safety barriers and an auxiliary power supply for up to 15 field devices (HART 5) or 62 field devices (HART 7) All process values are transmitted digitally. In multi-drop mode, all field device polling addresses must be unique in a range of 1-63 (depending on the HART Protocol Revision) and the current through each device is fixed to a minimum value (typically 4mA).

Use multi-drop connection for supervisory control installations that are widely spaced such as pipelines, custody transfer stations, and tank farms

iii)Split range network

split range with isolators

Split range control is a single control loop divided into two or more independent final control elements such as valves acting in different directions or in different steps. There are many ways to implement a split range control: software, valve calibration or by connecting two or more positioners to a single control signal (usually 4-20mA). A typical split range loop with two valves will be configured as follows:

 Intelligent Valve Positioner #1

Action: ATO (Air to Open)

Input current range: 4-12mA

Intelligent Valve Positioner #2

Action: ATC (Air to Close)

Input Current range: 12-20mA

When more than one positioner is installed in a single current loop, the HART loop address of each device must be set to 1, 2, or 3 (or other non-zero values) to allow a HART master to recognize each intelligent valve positioner when connected to all three devices on a single current loop.

iv)Wireless Mesh

wireless hart

As the need for additional process measurements increases, users seek a simple, reliable, secure and cost-effective method to deliver new measurement values to control systems without the need to run more wires.

 Each Wireless HART network includes three main elements:

Wireless field devices connected to process or plant equipment. These devices can be a device with Wireless HART built in or an existing installed HART-enabled device with a Wireless HART adapter attached to it.

Gateways enabling communication between the field devices and host applications connected to a high-speed backbone or other existing plant communications network.

A Network Manager responsible for configuring the network, scheduling communications between devices, managing message routes, and monitoring network health. The Network Manager can be integrated into the gateway, host application, or process automation controller.

Each device in the mesh network can serve as a router for messages from other devices. In other words, a device doesn’t have to communicate directly to a gateway, but just forward its message to the next closest device. This extends the range of the network and provides redundant communication routes to increase reliability

v)Control in field (PID)

control in field

Microprocessor-based smart instrumentation enables control algorithms to be calculated in the field devices, close to the process. Some HART transmitters and actuators support control functionality in the device, which eliminates the need for a separate controller and reduces hardware, installation, and start-up costs. Accurate closed-loop control becomes possible in areas where it was not economically feasible before. While the control algorithm uses the analog signal, HART communication provides the means to monitor the loop and change control set point and parameters. Placing control in the field enhances control functionality. Measurement accuracy is maintained because there is no need to transmit data to a separate controller. Control processing takes place at the high update rate of the sensor and provides enhanced dynamic performance.

Layer 2 (data layer)

Layer 2 (Data layer)

The data link layer provides a reliable, transaction-oriented communication path to and from field devices for digital data transfer.

The data link layer supports the application layer above it and requires services from the physical layer below it.

Divided into two sub layers: the logical link control responsible for addressing, framing, and error detection; and the medium access control that controls the transmission of messages across the physical link.

The elements of the HART frame are summarized as follows:

The delimiter is the first field in a HART message. It is used for message framing by indicating the position of the byte count. Three frame types are supported by the HART data link layer STX(0x2) indicates master to a field device, STX is generally Start of the transaction ACK(0x6) Slaves response to the STX, and finally the BCK(0x1) burst acknowledge frame periodically transmitted by a burst-mode device.

hart message format

The address field can be short or long. The protocol supports both five (5) byte unique addresses and one (1) byte polling addresses. The expansion bytes are optional. This field is 0–3 bytes long and its length is indicated in the delimiter.

The command byte encodes the master commands of the three categories: universal, common practice, and device-specific commands. The byte count character indicates the message length, which is necessary since the number of data bytes per message can vary from 0 to 25.

The data field is optional and consists of an integral number of bytes of application layer data.

The response message includes two status bytes at the beginning of the data portion of the message.

This check byte field is 1 byte long. The check byte value is determined by a bitwise exclusive OR of all bytes of a message including the leading delimiter.

 HART protocol is Master/Slave based communications protocol. Slave communication is initiated only when the Master requests. Two Masters can connect to each HART loop.

Primary Master can be the Distributed Control System, Programmable Logic Controller (PLC) or any Personal Computer. Secondary Master is generally a Handheld Terminal or another PC.

Slave Devices consist of Transmitters, Actuators, and controllers which respond to commands from Master.

Types of data link layer communications are Request/Response, Burst Mode, Events and Event Notifications.

Request response mode

HART Communications protocol uses Request/Response messages to access and change parameter values, invoke device methods, configure devices and in wireless HART manage the network devices

Burst mode

Allows the master to instruct the slave device to continuously broadcast a standard HART reply message.

Master receives the message in burst mode until it tells the slave to stop bursting.

Wireless HART devices support Burst mode whereas in Wired it is optional.

Events and event notification

Event notification publishes changes in the Device Status.

It is possible to specify limited set of bits that will trigger event notifications.

A de-bounce interval is configured.

Once the event is released, it is transmitted repeatedly until it is acknowledged.

Event notifications are built upon burst mode operation. The two distinct methods to display events are: Device Status and Common Practice Command 48.

Layer 3 (only for wireless communication) Network Layer

Layer 3

Network Layer (only for wireless Communication)

DLL moves packets between devices, hop by hop, the network layer moves packets end-to-end within the wireless network.

The 2.4 GHz ISM frequency band is divided into 16 non-overlapping frequency channels. Wireless HART instruments use a pseudo-random channel hopping sequence to reduce the chance of interference with other networks. Network layer security provides end-to-end data integrity and privacy across the wireless network.

Wireless HART is beyond the scope of this article

Layer 4(Transport layer)

Layer 4(Transport layer)


Block Data Transfer

It allows the device to transfer blocks of information.

It is classified as a Transport layer service.

Establishes connection between host and slave and transfers stream of data.

It maximizes the utilization of HART Communication.

Connection for this kind of communication is established by the command 111 to a specific port.

Command 112 is used to transfer data to and from the field device

layer 4

HART-IP, an Internet protocol (IP) enabled version of HART, was developed. HART-IP gives enterprise level systems and applications access for block data transfer, DATA HANDLING OVER ENTIRE NETWORK and integration of runtime measurement and device diagnostics information from HART devices through existing plant IP networks using Ethernet, Wi-Fi, fibre optic, packet-radio, satellite or 3G/4G cellular.


HART-IP is a simple-to-use, high-level application technology that  is independent of the underlying media, thus HART-IP operates with Ethernet media as well as mesh or ring topologies. Similarly, HART-IP can run on Power over Ethernet (PoE) for such infrastructure and devices. Speeds of 10 Mbit/s, 100 Mbit/s, and 1 Gbit/s are supported. Using a simple HART command, HART-IP delivers all requested smart device information – not just the Primary Variable. This makes HART-IP the most simple to use and suitable back haul network for Wireless HART gateways, wired HART multiplexers, remote I/O and native HART-IP field

devices. HART-IP offers straightforward access to large amounts of stranded HART measurement and diagnostic information from complex or multi-variable devices that concentrate measurements into a single output. It allows the information from these devices to be easily integrated with TCP/IP networks, without the need to go through any translation processes and with no loss of information

HART-IP uses conventional client-server architecture. A client can be either a host system or a host application while servers can be Wireless HART gateways, HART multiplexers, HART Remote I/O or individual HART devices. Client-server communication utilizes either/both UDP or TCP transport. Servers also support a minimum of two simultaneous client sessions.

Layer 7 Application layer

Layer 7 Application layer

Electronic Device Description Language (EDDL)

Is a machine readable language used to describe the devices in a common and consistent way. It describes the device, methods provided by device, measurement and device parameters supported, configuration information.

A DD file provides a picture of all the parameters and functions of a device in a standard language.

HART DDL is used to write the DD. Resembles C Language.

The application layer is HART. Because of this, access to Wireless HART is readily available by most host systems, handhelds, and asset management systems.

Accessing Data

The most common data types are Process Variable/Primary Variable (PV), a percentage of range, and a digital reflection of analog mA signal or the device status.

These values are mapped to the HART protocol PV, Secondary Variable (SV), Tertiary Variable(TV), Fourth Variable (FV).

Example: Mass flow meter has the derived values obtained.

PV – mass flow value.

SV – Static Pressure.

TV – Temperature.

FV – Digital mA signal reflectionThese mappings are user selectable.

Wiring Parameters and Commanding Devices. HART also describes how to write data back to the instrument.

HART also supports the commands for calibrating the instruments based on the application requirements.

For Wired Devices all the communications are carried out over 4-20 mA current loop wiring.

For Wireless HART devices the communication is carried out over–the–air through IEEE 802.15.4 radios.

Design Approach

The HCF (HART Communications Foundation) provides HART specifications that can be used by suppliers to design and build devices, tools, and applications.

The device description DD.

HART messages.

Service or Protocol Structure.

HART Commands which are the content of HART messages.


Analysis of motor/pump vibration

Vibration in a pump can be due to

1.Electrical imbalance

2.Mechanical unbalance – motor, coupling, or driven equipment

3.Mechanical effects – looseness, rubbing, bearings, etc.

4.External effects – base, driven equipment, misalignment, etc.

5.Resonance, critical speeds, reed critical etc

To solve a vibration problem one must differentiate between cause and effect 

Is the vibratory force the cause of the high levels of vibration or is there a resonance that amplifies the vibratory response.May be the support structure is just not good enough to minimize the displacement.


There are many different forces and interactions as a result of the power source and the interactions between the stator and rotor.


These can be classified as (frequency vibration oversize, symmetry, load, and unbalance)

Can be remembered as “FOULS” in a pump/motor

“F” stands for frequency of vibration like twice line frequency vibration,

“O” stands for oversize coupling and parts

“U” stands for unbalance like motor, thermal, driven machine etc

“L” stands for load related vibration

“S” stands for Symmetry of rotor/stator


“F” category

1.Twice Line Frequency Vibration:

2.One Times Line Frequency Vibration:

3.Rotor Bar Passing Frequency vibration:

4.Mode Shapes and Natural Frequencies of core Vibration 


“O” category

5.Oversize Coupling and parts: 

“U” category

6.Motor Unbalance.

7.Thermal Unbalance

8.Coupling Unbalance:

9.Driven Machine Unbalance: 

“L” category

10.Load Related Magnetic Force Frequencies and Mode Shapes 

“S” category

11.Elliptical stator due to Fundamental Flux:

12.Non Symmetrical Air-gap:

13.Eccentric Rotor:

14.Broken Rotor Bar:

15.Maintaining Balance in the Field:

16.Forcing Frequency Response Vibration


A brief explanation is as follows

1.Twice Line Frequency Vibration:

The power source of a pump is a sinusoidal voltage that varies from positive to negative peak voltage in each cycle. Many different problems either electrical or mechanical in nature can cause vibration at the same or similar frequencies

A power supply produces an electromagnetic attracting force between the stator and rotor which is at a maximum when the magnetizing current flowing in the stator is at a maximum either positive or negative at that instant of time.As a result there will be 2 peak electromagnetic forces (causes vibration here) during each cycle of the voltage or current wave reducing to zero at the point in time when the current and fundamental flux wave pass through zero


This will result in a frequency of vibration equal to 2 times the frequency of the power source (twice line frequency vibration). This particular vibration is extremely sensitive to the motor’s foot flatness, frame and base stiffness and how consistent the air gap is between the stator and rotor, around the stator bore. It is also influenced by the eccentricity of the rotor.

2.One Times Line Frequency Vibration:

Although not nearly as prevalent as twice line frequency vibration, one times line frequency vibration can exist. Unbalanced magnetic pull may result in vibration at line frequency (one times line frequency) as well as the usual twice line frequency vibration. If the rotor or stator moves from side to side, the point of minimum air gap may move from one side of the motor to the other. When the frequency of this motion corresponds to the frequency of the travelling flux wave, the unbalanced magnetic pull will shift from side to side with the point of minimum gap, resulting in vibration at line frequency. This line frequency vibration is normally very small or non-existent, but if the stator or rotor system has a resonance at, or near, line frequency, the vibration may be large.

3.Rotor Bar Passing Frequency Vibration:

High frequency, load-related magnetic vibration at or near rotor slot passing frequency is generated in the motor stator when current is induced into the rotor bars under load. The magnitude of this vibration varies with load, increasing as load increases. The electrical current in the bars creates a magnetic field around the bars that applies an attracting force to the stator teeth. These radial and tangential forces which are applied to the stator teeth create vibration of the stator core and teeth. This source of vibration is at a frequency which is much greater than frequencies normally measured during normal vibration tests. Due to the extremely high frequencies, even very low displacements can cause high velocities if the frequency range under test is opened up to include these frequencies. Though these levels and frequencies can be picked up on the motor frame and bearing housings, significant levels of vibration at these higher frequencies will not be seen between shaft and bearing housing where they could be damaging.


4.Mode Shapes and Natural Frequencies of Core Vibration:

Under the applied magnetic forces (due to phase current) the stator core is set into vibration in the same manner that a ring of steel would respond if struck. Depending upon the modal pattern and frequencies of the exciting force, as described above, the stator would vibrate in one or more of its flexural modes m of vibration.


5.Oversize Coupling:

One consideration in coupling selection is coupling size. The coupling should be large enough to handle the application, including the required service factor, but should not be exceptionally large. Potential results of oversize couplings are:

*Increased motor vibration due to increased coupling unbalance and/or a change in the critical speed or rotor response due to increased weight. This is particularly true for flexible shaft machines.

*A greatly oversize coupling can result in greatly severe shaft bending, excessive vibration, and, heavy rubbing of seals, ultimately resulting in catastrophic shaft failure.

6.Motor Unbalance:

Balancing is required on all types of rotating machinery, including motors, to obtain a smooth running machine. This is performed in the factory in a balance machine at a level of precision determined by the motor speed, size, and vibration requirements. Fundamental requirements for precision balance on any machine are:

*Parts must be precision manufactured for close concentric and minimal unbalance individually.

*Looseness of parts, which can result in shifting during operation, causing a change in balance, must be avoided or minimized.

*Balance correction weights should be added at or near the points of unbalance.

7.Thermal Unbalance:

Thermal unbalance is a special form of unbalance. It is caused by uneven rotor heating or uneven bending due to rotor heating. The proper solution is to determine the reason for uneven heating affecting shaft straightness, and fix the rotor.All rotors will have some change in vibration in transitioning from a cold state to a hot one.However, if the application is one of continuous duty, and, vibration levels are not excessive during start-up (i.e. motor cold), it is permissible to allow more change cold to hot without any damage to the motor. In these situations if the lowest vibration levels are desired at operating conditions, a hot trim balancing procedure can be performed. To perform this procedure, run the motor until all conditions thermally stabilize, and quickly perform a trim balance. If necessary,run the motor again after the initial trial weights have been installed and let the motor thermally stabilize before taking additional vibration measurements for final weight correction

8.Coupling Unbalance:

Use of a proper key and a balanced coupling leaves the machine alignment and mounting and the driven equipment balance as the remaining major factor in system vibration.

9.Driven Machine Unbalance:

Under normal circumstances, the unbalance of the driven machine should not significantly affect the motor vibration. However, if the unbalance is severe, or if a rigid coupling is being used, then the unbalance of the driven machine may be transmitted to the motor

10.Load Related Magnetic Force Frequencies and Mode Shapes 

The frequencies of the load related magnetic forces applied to the stator teeth and core equal the passing frequency of the rotor bars. A magnetic force is generated at the passing frequency of the rotor slot (FQR), which is motor speed in revolution per second times the number of rotor slots The forces applied to the stator teeth are not evenly distributed to every tooth at any instant in time; they are applied with different magnitudes at different teeth, depending upon the relative rotor-and stator-tooth location. This results in force waves over the stator circumference. The mode shape of these magnetic force waves is a result of the difference between the number of rotor and stator slots


11.Elliptical stator due to Fundamental Flux:

For 2-pole motors the Electro-mechanical force will attempt to deflect the stator into an elliptical shape. The primary resistance to movement is the strength of the core back iron and the stiffness of the housing around the stator core, which is restraining the core’s movement.


12.Non Symmetrical Air-gap:

Twice line frequency vibration levels can significantly increase when the air gap is not symmetrical between the stator and rotor.


13.Eccentric Rotor:

An eccentric rotor, which means the rotor core OD is not concentric with the bearing journals, creates a point of minimum air gap which rotates with the rotor at one times rotational frequency. Associated with this there will be a net balanced magnetic force acting at the point of minimum air gap, since the force acting at the minimum gap is greater than the force at the maximum gap.This net unbalance force will rotate at rotational frequency, with the minimum air gap, causing vibration at one time rotational frequency.The flux causing the magnetic force is the fundamental flux wave, which rotates around the stator at the synchronous speed of the motor. The rotor attempts to keep up with the rotating flux wave of the stator, but the rotor slips behind the stator field as needed to create the necessary torque for the load. When the high point of the rotor (point of minimum air gap) aligns with the high point (maximum) of the stator flux, the force will be a maximum, and then it will decrease, becoming small under a point of minimum flux. Thus, an unbalance force is created which rotates at rotational speed and changes in magnitude with slip. The end result is a one times rotational speed vibration, which modulates in amplitude with slip. This condition occurs at no load or full load.


14.Broken Rotor Bar:

If a broken rotor bar or open braze joint exists, no current will flow in the rotor bar.As a result the field in the rotor around that particular bar will not exist. Therefore the force applied to that side of the rotor would be different from that on the other side of the rotor again creating an unbalanced magnetic force that rotates at one times rotational speed and modulates at a frequency equal to slip frequency times the number of poles. If one of the rotor bars has a different resistivity a similar phenomenon (as in the case of a broken rotor bar) can exist.Broken rotor bars or a variation in bar resistivity will cause a variation in heating around the rotor.This in turn can bow the rotor, creating an eccentric rotor, causing basic rotor unbalance and a greater unbalanced magnetic pull.


15.Maintaining Balance in the Field:

When a finely balanced high speed motor is installed in the field, its balance must be maintained when the motor is mated to the remainder of the system. In addition to using a balanced coupling, the proper key must be used.One way to achieve a proper key is to have the shaft key way completely filled, with a full key through the hub of the coupling and the entire key outside the coupling crowned to match the shaft diameter. A second approach is to use a rectangular key of just the right length so that the part extending beyond the coupling hub toward the motor just replaced the unbalance of the extended open key-way. This length can be calculated if the coupling hub length and key-way dimensions are known.An improper key can result in a significant system unbalance, which can cause the vibration to be above acceptable limits

16.Forcing Frequency Response Vibration

*Weak Motor Base:

If the motor is sitting on a fabricated steel base, such as a slide base, then the possibility exists that the vibration which is measured at the motor is greatly influenced by a base which itself is vibrating. Essentially, this requires that support vibration near the motor feet to be less than 30% of the vibration measured at the motor bearing. To test for a weak base, measure and plot horizontal vibration at ground level, at bottom, middle, and top of the base, and at the motor bearing. If the motor is on a rigid base, the vibration at the bearing will closer to .25 mils but if support is not rigid it will be showing 2.50 mils as shown below


A weak motor base usually results in high 1x vibration, usually in the horizontal direction as shown above. However, it may also result in high 2X (twice rotational frequency) or 2f (twice line frequency) vibration, which also is a common vibration frequency in motors. The support posts must be tied together and heavily stiffened with the intention to meet the criteria for a “massive foundation.”Even where resonance of the base is not a factor, heavy stiffening of a light support structure can greatly reduce vibration.

*Reed Critical Base Issues:

A vertical motor’s reed critical frequency is a function of its mass, distribution of mass, and base geometry. The reed critical should not be confused with the motor rotor’s lateral critical speed. If the motor’s operating speed (or any other frequency at which a forcing function is present) coincides with the reed critical, great amplification in the vibration amplitude will occur Machine weight, center of gravity location, and static deflection. Bases found in typical installations are not as stiff, and correspondingly, the reed critical frequency will be lowered. If the reed critical drops into a frequency at which there is a forcing function present (most commonly the operational speed), the reed critical frequency will have to be changed. Usually, this is not difficult to do, and is most commonly accomplished by either changing the stiffness of the base, or by changing the weight of the base/motor. Where the reed critical drops below the operational speed to about 40% to 50% of running speed, this can result in sub-harmonic vibration at the system resonant speed in motors with sleeve guide bearings.

*Resonant Base:

If the motor’s operating speed (or any other frequency at which a forcing function is present) coincides with the base resonant frequency, great amplification in the vibration amplitude will occur. The only solution to this problem is to change the resonant frequency of the base. Usually, this is not difficult to do, and is most commonly accomplished by either changing the stiffness of the base, or by changing the weight of the base/motor.

*Bearing Related Vibration:

Sleeve bearing machines may occasionally experience “Oil Whirl” vibration, which occurs at a frequency of approximately 45% of running speed. This may be quite large, particularly if there is a critical speed at or just below 45% of running speed, which is referred to as an “oil whip” condition. Other than basic bearing design considerations which will not be dealt with here, a common cause is high oil viscosity due to low oil temperature in flood lubricated motors operating in cold ambient conditions.Similar sub-harmonic vibration, but low in amplitude, may occur in ring lubricated bearings, probably due to marginal lubrication. Other causes of vibration are journal out of roundness or bearing misalignment.


Can be done by

*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, displacement emphasizes low frequencies, and velocity gives equal emphasis to all frequencies.

*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. 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 a 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.

*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.


Maintenance Items

-Check for loose bolts – mounting or other loose parts

-Keep motor clear of dirt or debris

-Check for proper cooling and inlet temperatures or obstructions such as rags, lint or other enclosures

-Check Bearing and stator Temperatures

-Lubricate as recommended

-Check proper oil levels

Check vibration periodically and record using a check list as shown below

*Are all bolts tight? Has soft foot been eliminated?

*Is hot alignment good? If it’s not possible to verify hot alignment, has cold alignment been verified (with appropriate thermal compensation for cold to hot)?

*Is any part, box top cover, piping vibrating excessively (i.e. are any parts attached to motor in resonance)?

*Is the foundation or frame the motor is mounted to vibrating more than 25% of motor vibration (i.e. is the motor base weak or resonant).

*Is there any looseness of any parts on motor or shaft?

*Integrity of fans and couplings – have any fan blades eroded/broken off, are any coupling bolts loose/missing, is coupling lubrication satisfactory? 

*Ideally, vibration measurements should be obtained with the motor operating under the following conditions:

*Loaded, Coupled, Full Voltage, All Conditions Stabilized

Normal operating conditions

* First measurement to be obtained.

*Represents state of machine in actual operation.

* May indicate which test should be taken next.

Unloaded, Coupled, Full Voltage:

* Removes load related vibration, while everything else remains the same.

*Not always possible to get to zero load, but some reduced load is usually possible.

Unloaded, Uncoupled, Full Voltage:

*Removes all effects of coupling and driven machine.

*Isolates motor/base system.

Unloaded, Uncoupled, Reduced Voltage (25% if possible):

*Effect of magnetic pullover forces minimized (most effective use is in comparison to vibration at full voltage,

*25% usually only possible at motor service shop or motor manufacturers facility. If motor is a Y-Δ

connected motor, then Y connection is effectively 57% voltage as compared to Δ connection at the same terminal voltage. A comparison of vibration under both connections will reveal voltage sensitivity of motor.

Unloaded, Uncoupled, Coast Down:

*Will make any resonance/critical speed problem apparent for entire motor/base/driven equipment system.


As motor ages, the vibration levels may slowly increase.There may be a multitude of reasons of why the levels may increase over time:

Degradation of the bearings (sleeve bearings) loosening of rotor bars

Accumulation of debris in the oil guards, between rotor and stator, etc.

Changes in mounting conditions: deterioration of grouted base, changes in alignment/soft foot, etc

Loosening of things mounted to the motor

The factor limiting the vibration limits at these levels is the motor bearings. Generally, sleeve bearings (as compared to anti friction bearing motors) are more restrictive in terms of vibration limits. Sleeve bearing motors can operate continually at one-half their diametrical bearing clearance, without any damage.They can operate at slightly higher levels for short periods of time as well, but these higher limits must be established with the motor manufacturers.If the motor is sitting on a weak base, higher housing vibration limits and shaft vibration limits (if measured by shaft stick and not by a proximity probe) can be tolerated.Vibration problems can vary from a mere nuisance to an indication of imminent motor failure. With solid knowledge of motor fundamentals and vibration analysis, it is possible to identify the root cause of the problem, and more significantly correct.


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Oil in Water Analyser


BSW Analyser


Capacitive Level Transmitter


LRV and URV Level Transmitter


Instrument Loop Diagram


Laser Level Transmitter


Turbine Flow Transmitter


Zero Suppression and Elevation


Bently Nevada 3500 VMS


Control Valve Servicing


Safety Integrity Level


Instrumentation Working Principle


Instrumentation Gland Sizes


LRV and URV of DP level transmitter


Instrumentation working principle continued


Level measurement using Pressure gauge


Tips and tricks in field Instrumentation


Data Communication Protocol


Pressure Unit Conversion


Calibration of  GWR level transmitter


Control Valves


ERS Level transmitter Parameters


Calibration of wet leg tube Level transmitter


Calibration of capillary type Level transmitter


mV conversion chart


Gulf JOB



Reynolds Number


Calibration of displacer type LT


My profile


Chemical hazard pictogram



RTD conversion chart


Ingress Protection




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Instrumentation tube fittings

Tube fittings are used to join or connect a tube end to another member, whether that other member be another tube end such as through T-fittings and elbow fittings, for example, or a device that needs to be in fluid communication with the tube end, such as for example, a valve.

Any tube fitting must accomplish two important functions within the pressure, temperature and vibration criteria that the tube fitting is designed to meet. First, the tube fitting must grip the tube end so as to prevent loss of seal or tube blow out. Secondly, the tube fitting must maintain a primary seal against leakage

The different types of tubing are

a) Flareless Compression Type (Single Ferrule)

(b) Flareless Compression Type (Double Ferrule)

(c) Bite Type

(d) Flared Fitting


The important parts of fitting are


Before that male and female threads are distinguished as follows


The different types of fittings based on type of threads is as below


The fitting can be of brass, carbon steel, SS 316/316L,Duplex steel, super duplex steel, Super 6Mo, Monel 400, Alloy 825,Alloy 625, Alloy Carbon 276, Titanium grade 2 and 5 and PVC

The fittings can be classified as

  1. 1.NIPPLE (both side NPT/BSP)

    2.UNION (both side Metric or fractional OD with end caps)

    3.CONNECTOR (One side Metric/Fractional OD compulsory and other side may be NPT/BSP)

    4.CONVERTER (Fraction to metric conversion, i.e. one side end tube of inch and other side OD metric conversion with end caps )

    5.ADAPTER (one side tube end with NPT/BSP/METRIC/FRACTIONAL and other side with machine threaded NPT/BSP/METRIC/FRACTIONAL/SPECIAL THREADED)

    6.REDUCER (one side end tube with inch/metric and other side threaded with inch/metric, but of different sizes. Here it should be noted that if one side is metric other side will also be metric, only its size changes)

    7.PLUG (one side NPT/BSP/METRIC OD and the other side blinded)

    8.ELBOW (in shape of our elbow)

    9.T (in the shape of T)

    10.CROSS (in the shape of cross)

    11.BARBED (simply push the fitting inside the tube)

    12.INSERT (inserting fitting inside connecting tubes with different ends)


Let me explain in detail

1.NIPPLE {both side NPT or both side BSP}:

Here are some situations in which two female ends in a tube system need to be connected. The fitting for this job is a nipple. A nipple is a fitting with two male-threaded ends. It will be having either both side NPT or BSP.

Nipple is used to connect two other fittings as shown below



A union allows the convenient future disconnection of tubes for maintenance or fixture replacement. A union allows easy connection and disconnection, multiple times if needed. This type of fitting has either metric of fractional OD with end caps on both sides



This will be having one side compulsorily Metric fractional OD and another side NPT or BSP




A converter have port one side as tube end (inch) and port 2 as OD metric conversion (with end caps) which means if port 1 is metric then port 2 will be inch and is used for inch metric conversion




 These fittings are designed to change the end type of a tube, allowing it to connect to fittings and tubes of many sizes. They can have threaded or slip socket ends to connect to an endless variety of tubes and fittings. Adapters can be either male or female-threaded, as well as socket or spigot.

 An adapter have port one side as turned end tube (with NPT /BSP/METRIC/FRACTIONAL measurements) and port two side as machined end tube or threaded  NPT /BSP/METRIC/FRACTIONAL/special threads like barbed thread but of different sizes. Thus in an adapter both sides will be of different types threading.



A reducer allows for a change in tube size to meet hydraulic flow requirements of the system or adapt to existing tube of a different size.

Reducer have port one side as (tube end) and port two as machine threaded but the remains same type (either inch or metric) and obviously of different sizes in order to reduce. This means if port one is metric then port 2 will also be metric but size changes.



A PLUG HAVE having one side as NPT/BSP/METRIC/FRACTIONAL and the other end as blinded.Plugs are like caps, but instead of stopping the flow in a tube, they stop the flow in a fitting.

They are put on the end of a pipeline that does not need to be connected to another pipe. They can stop a tube line that you plan on expanding later or give you easy access to a system when needed.


8.ELBOW in the shape of elbow

An elbow is installed between two lengths of pipe (or tubing) to allow a change of direction, usually a 90° or 45° angle; 22.5° elbows are also available. The ends may be machined for butt welding,threaded(usually female). When the ends differ in size, it is known as a reducing (or reducer) elbow.


9.T (in the shape of T)

A tee, the most common pipe fitting, is used to combine (or divide) fluid flow. It is available with female thread sockets, solvent-weld sockets or opposed solvent-weld sockets and a female-threaded side outlet. Tees can connect tubes of different diameters or change the direction of a tube run, or both


Ts are of many types, some of them are

This will combine or reduce a flow.

Types of T are

a.Union T


b.Drop size T


c.Run T here a portion of flow from main flow will be diverted into a side branch


d.Branch T


10.CROSS in the shape of cross

Crosses can add a great deal of structural integrity to a framework for multiple flow direction in a tube


11.BARBED (Because they’re insert fittings, they’re sized by the inside diameter (ID) of tubing. Fortunately, most tubing has the ID printed right on it, making it easy to find the right size. Installing barbed fittings is simple, as well: simply push the fitting inside the tube)




This is used for inserting fitting inside connecting tubes with different ends.


Most popular make of fittings are Parker, Swagelok, Midland, HOKE, MANNESMANN, FESTO, HY-LOK, FESTO etc



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Radar (Non Contact) Level Transmitter working and Parameters

Working Principle

A radar signal is emitted via a horn antenna, reflected on the measuring surface and received with a time delay (Doppler’s effect).The frequency difference is transformed via an electronic circuit into the difference of the frequency spectrum and then the distance is calculated.


Important Parameters and settings of a CONE type Radar LT (Rosemount 5600)

Consider a tank as shown below

Untitled - Copy

LRV = 0 mm

URV = 10600 mm

Tank height = 11310 mm

Distance Offset = 0 mm (normally assumed zero)

Minimum Level offset = 0 mm (normally assumed zero)

Calibration distance = 0 mm (normally assumed zero)

Upper Null Zone = 500 mm

Antenna Cone 6” PTFE

Tank type Vertical cylinder

Tank bottom type Flat

Tank environment

  1. 1.Process condition Rapid change OFF

    2.Product DC between 2.5 and 4 (here crude oil)

    3.Basic volume Calculation method not changed

Tank Presentation

Negative level as 0

No alarm if empty ON

No alarm if full   ON

Slow search OFF

Bottom echo visible ON

General Threshold

3340 mV


No. Of sensors 0

Type RTD PT 100


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