CALIBRATION PROCEDURE

Calibration Procedure For 248/644/3144 Temperature Transmitter

INDEX

                       

1.      Purpose

2.      Scope

3.      General Safety & permit to work.

4.      Tools & Materials Required

5.      Calibration Procedures

6.      Shop calibration procedure

ABBREVIATIONS

1.      TT                 - Temperature transmitter

2.      SMART       - Signal Modulated Addressable Remote Transducers.

3.      PPE              - Personal Protective Equipment.

4.      Non-IS         - Non Intrinsic Safe.

5.      LRV             - Lower Range Value.

6.      URV            - Upper Range Value.

7.      HART          - High way Addressable Remote Transducer.

8.      DCS             - Distributed Control System

9.      ILD              - Instrument Loop Drawing

10.  RIB              -  Remote Instrument Building

1.      Purpose

Ø  To provide a Standardized set of Guidelines for the calibration of 248/644/3144 Temperature transmitter.

2.          Scope

Ø  This Calibration procedure is applicable for all 248/3144 SMART type Rosemount Temperature Transmitters.

3.            Permit to Work & General safety

Ø  Obtain the necessary work permit.

Ø  Ensure appropriate PPE used.

Ø  Make sure whether any safety personal assistance is required.

Ø  Make sure whether the concerned loop is related to control or any trip systems, take necessary action before proceeding to attend the transmitter.

4.       Tools & Materials Required.

Ø  Multimeter.

Ø  Temperature Calibrator.

Ø  HART communicator.

Ø  Required tools.

 

For oxygen service use oxygen clean calibrator & oxygen clean  tubes and fittings

 5.          Calibration Procedures 

5.1. On line Hart communicator

Ø  Note down the transmitter range & unit from master document in the work shop.

Ø  Before checking/adjusting the transmitter, record the actual temperature indication in the control room.

Ø  Before proceeding to check the transmitter, aware of the service conditions.

OXYGEN SERVICE Ø  Do not use stain gloves. Ø  Do not use oil & grease. Ø  Do not use Non –IS Calibrator and electronic devices.

Ø  Ensure the temperature is having Trip; follow the procedure for Trip Override.

Ø  Ensure sensor is Thermocouple / RTD.

Ø  Remove the sensor leads & insulate.

Ø  Ensure the grounding connection.

Ø  Connect the calibrator leads in the sensor terminals.

Ø  Connect the Hart communicator in transmitter loop terminals.

Ø  Refer HART menu tree for guidance.

 

Ø  Select Device Setup & enter

Ø  Select Diag/ Service & enter

Ø  Select Calibration & enter

Ø  Select sensor 1 trim & enter

Ø  Select sensor 1 Input trim & enter

Ø  Set the control loop manual & O.K

Ø  Adjust the calibrator to the desired lower trim value.

Ø  Select O.K once the temperature stabilizes

Ø  If deviation is observed, do the Trim procedure again.

Ø  Adjust the calibrator to the desired upper trim value.

Ø  Select O.K once the temperature stabilizes

Ø  If deviation is observed, do the Trim procedure again.

Ø  Verify the reading with control room operator.

Ø  In case of field mounted display is not applicable Ensure that the HART reading is the same as calibrator reading.

Ø  If the accuracy is not with in the limits do the calibration again. 

Ø  Ensure the power supply voltage to the transmitter

Ø  Repeat the calibration and observe the repeatability of the transmitter readings in the multimeter by up scale and down scale.

Accuracy is +/- 0.5 deg C  for 248 Transmitter

Accuracy is +/- 0.12 deg C  for 3144 Transmitter with RTD sensor

Ø  Record all the calibration readings and transmitter manufacturer’s informations in the calibration report.

Ø  If the loop under MANUAL or TRIP override, observe the loop stability

     And normalize to auto and remove the trip Over ride.          

Ø  Close the work permit.

Ø  Submit work order for supervisor approval and file the same.

Report to supervisor if error is not with in the limits after calibration. Remove transmitter to shop for further investigation.

5.      Shop Calibration Procedure

Ø  Verify the transmitter range & unit from master document in the work shop

Ø  Clean the transmitter.

Ø  Connect 24Vdc from calibrator with 250 ohms loop resistance in series.

Ø  Connect multimeter in series with the transmitter.

Ø  Connect HART communicator and check LRV & URV.

Ø  Apply the temperature corresponding to LRV and note down the mA in the multimeter.In case of any error, follow the procedure in step 5.

Ø  Apply the temperature corresponding to URV and note down the mA reading, In case of any error, follow the procedure in step 5.

Report to supervisor if error is not with in the limits after repeat calibration.

Ø  If abnormal found, replace the transmitter or repair it accordingly

Ø  Do the calibration procedure again.

Ø  Apply temperature corresponding to intermediate values and note down the readings.

Ø  Record all the calibration readings and transmitter manufacturer’s informations in the calibration report.

INSTRUMENTATION ENGINEERING INTERVIEW QUESTIONS(PART 5)

PART 5

1.What is furnace draft control?
Balanced draft boilers are generally used negative furnace pressure. When both forced draft and induced draft are used together, at some point in the system the pressure will be same as that of atmosphere. Therefore the furnace pressure must be negative to prevent hot gas leakage. Excessive vacuum in the furnace however produces heat losses through air infiltration. The most desirable condition is that the one have a very slight negative pressure of the top of furnace.

2.What is intrinsically safe system?
Intrinsic safety is a technique for designing electrical equipment for safe use in locations made hazardous by the presence of flammable gas or vapours in the air. Intrinsically safe circuit is one in which any spark or thermal effect produce either normally or under specified fault conditions is incapable of causing ignition of a specified gas or vapour in air mixture at the most ignited concentration.

3.What is zener diode? What is voltage regulator?
The breakdown region of a p-n diode can be made very sharp and almost vertical diodes with almost vertical breakdown region are known a s zener diodes. A zener diode operating in the breakdown region is equivalent to a battery. Because of this current through zener diode can change but the voltage remains constant. It is this constant voltage that has made the zener diode an important device in voltage regulation.
Voltage regulator: The output remains constant despite changes in the input voltage due to zener effect.

4.What is force balance principle? State some of its’ advantages?
Force balance principle: A controller which generates an output signal by opposing torque. The input force is applied on the input bellows which moves the beam. This crackles nozzle back pressure. The nozzle back pressure is sensed by the balancing bellows which brings the beam to balance. The baffle movement is very less about 0.002 for full scale output.
Advantages:
1. Moving parts are fewer.
2. Baffle movement is negligible
3. Frictional losses are less

5.What is motion balance principle?
A controller which generates an output signal by motion of its parts. The increase in the baffle is to move towards the nozzle. The nozzle back pressure will increase. This increase in the back pressure acting on the balancing bellows, will expand the bellows. The nozzle is moved upward due to this. The nozzle will move until motion almost equals the input baffle motion.

6.How will you test a transistor with a multimeter?
1. Emitter +ve of meter and base -ve output =Low resistance
2. Emitter -ve of meter and base +ve output =High resistance
3. Collector +ve and base -ve output =Low
4. Collector -ve and base +ve output =Low
Emitter: Collector = High resistance
PNP: Opposite Results

7.Explain ratio control system?
A ratio control system is characterized by the fact that variations in the secondary variable don’t reflect back on the primary variable. A ratio control system is the system where secondary flow is hold in some proportion to a primary uncontrollable flow.
If we assume that the output of a primary transmitter is A. and the output of the secondary transmitter is B, and that the multiplication factor of the ratio relay is K, then for equilibrium conditions which means set valve is equal to measured valve, we find the following relation:
KA-B=0 or B/A = K where ‘K’ is the ratio setting off the relay.

8.What is solenoid valve? Where it is used?
A solenoid is electrically operated valve. It consists of solenoid coil in which magnetic plunger moves. This plunger is connected to the plug and tends to open or close the valve. There are two types of solenoid valves:
1. Normally Open
2. Normally closed
Use: It is used for safety purpose in different electric work

INSTRUMENTATION ENGINEERING INTERVIEW QUESTIONS(PART 4)

PART 4

1.What is the use of single seated valve?
The single seated valve is used on smaller sizes where an absolute shut off is required. The use of single seated valve is limited by pressure drop across the valve in the closed or almost closed position.

2.What is the use of double seated valve?
In double seated valves the upward and downward forces on the plug due to reduction of fluid pressure are nearly equalized. It is generally used on bigger size valves and high pressure systems. Actuator forces required are less.

3.What is the use of valve positioner?
Valve positioner can be used for following reasons:
1. Quick action
2. Valve hysterisis
3. Viscous liquids
4. Split range.
5. Line pressure changes on valve
6. Bench set not standard
7. Reverse valve operations

4.What are primary elements of measuring pressure? Which type of pressure can be measured by these elements?
Primary elements of measuring pressure are:
1. Bourdon Tube
2. Diaphragm
3. Capsule
4. Bellows
5. Pressure springs
These elements are known as elastic deformation pressure elements.

5.Name different types of bourdon tubes?
Types of bourdon tubes:
1. C type
2. Spiral
3. Helix

6.What are different types of control valves?
The commonly used control valves can be defined as follows:
a. Depending on Action:
Depending on action there are two types of control valves
1. Air to close 
2. Air to close
b. Depending on body:
Depending on body there are 4 types of control valves
1. Globe valves single or double seated
2. Angle valves
3. Butterfly valves
4. Three way valves

INSTRUMENTATION ENGINEERING INTERVIEW QUESTIONS(PART 3)

PART 3

1.How is automatic reference junction compensation carried out in temperature recorders?
In automatic reference junction compensation, variable nickel resistor is used. As the temperature changes, so does its resistance. This reference junction compensator is located, so that it will be at the temperature of the reference junction. The reference junction is at the poset where the dissimilar wire of the thermocouple is rejoined. This joint is invariably at the terminal strip of the instrument.

2.What are de-saturators?
When, in some processes, e.g. batch processes, long transient responses are expected during which a sustained deviation is present the controller integral action continuously drives the output to a minimum or maximum value. This phenomenon is called ‘integral saturation of the control unit’. When this condition is met, then this unit is de-saturated.

3.Explain the working of Rota meter.
Variable area meters are special form of head meters. Where in the area of flow restrictor is varied. So as to hold the differential pressure constant. The rota meter consists of a vertical tapered tube through which the metered fluid flows in upward direction. As the flow varies the ‘float’ rises or falls to vary the area of the passages that the differential across it balances the gravitational force on the ‘float’. The differential pressure is maintained constant. The position of the ‘float’ is the measure of the rate of flow.

4.What is the working principle of the magnetic meter?
An electric potential is developed when a conductor is moved across the magnetic field. In most electrical machinery the conductor is a wire. The principle is equally applicable to a moving, electrically conductive liquid. The primary device of commercial magnetic meters consist of straight cylindrical electrically insulated tube with a pair of electrodes nearly flush with the tube walls and located at opposite end of a tube diameter. This device is limited to electrically conducting liquids. The magnetic meter is particularly suited to measurement of slurries and dirty fluids.

5.Explain the mechanism behind the turbine meter?
Turbine meters consist of straight flow tube within which a turbine or fan is free to rotate about it s axis which is fixed along g the centre line of the tube. Mostly, a magnetic pick up system senses the rotation of the rotor through the tube walls. The turbine meter is a flow rate device
, since the rotor speed is directly proportional to the flow rate. The output is usually in the form of electric pulses from the magnetic pick up with a frequency proportional to the flow rate.

6.How would you choose differential range?
The most common range for differential range for liquid measurement is 0-100. This range is high enough to minimize the errors caused by unequal heads in the seal chambers. It is also dependent on the differences in the temperature of the load lines. The 100 range permits an increased in capacity up to 400. While decrease down up to 20 by merely changing the range tubes or range adjustments.

INSTRUMENTATION ENGINEERING INTERVIEW QUESTIONS AND ANSWERS (PART 2)

PART 2

1. How D.P. transmitter can be applied to close tank?
In closed tank, bottom of the tank is connected to the high pressure side of the transmitter. Top of tank is connected to the lower pressure side of the transmitter. In this way vessel pressure can be measured.

2. How D.P. transmitter can be applied to open tank?
In open tank the lower pressure side is vented to the atmosphere. All pressure is applied to the high pressure side. This vessel pressure is measured through high pressure side.

3. Explain the working of an electronic level troll?
The variation in level of buoyancy resulting from a change in liquid level varies the net weight of the displacer increasing or decreasing the load on the torque arm. This change is directly proportional to change in level and specific gravity of the liquid. The resulting torque tube movement varies the angular motion of the rotor in RVDT providing a rotor change proportional to the rotor displacement, which is converted and amplified to a D.C. current.

4. Explain the working of an enraf level gauge?
Enraf level gauge is based on the ser powered null balance technique. A displacer serves as continuous level sensing element. A two phase ser motor controlled by a capacitive balance system winds unwinds the the measuring wire until the tension in the weight springs is in balance with the weight of the displaced part immersed in the liquid. The sensing system in balance measures the two capacitance formed by the moving central sensing rod provided by the two capacitor plates and the si plates.

5. What is the constant voltage unit?
The constant voltage circuit consists of a rectifier, CR and a filter capacitor. It is followed by two stages of zener regulation. Abridge configuration is provided to lamp line voltage zener regulation. Regulation 1 and regulation 2 provides relatively provide constant current. Resistors form a bridge that may remoment line voltage effects.

6. Explain the burnout feature.
Burnout provides the warnsug feature of driving indicator at the end of scale, if the input circuit is open. A burnout resistor is provided which develops a voltage drop between the measuring circuit and amplifier. The polarity of the signal determines the direction of the servo drive upon an open circuit in the input.
Upscale burnout: R value 10 M
Downscale burnout: R value 22 M

7. Why thermo wells are used? What materials are used in thermo wells?
In numerous applications, it is neither desirable nor practical to expose a temperature sensor directly to a material. Wells are therefore used to protect against damage corresion, arosion, aborsion and high pressure processes. A thermo well is also useful in protecting a sensor from physical damage during handling and normal operations.
Materials used in thermo wells: Stainless steel, Inconel, Monel, Alloy Steel, Hastelloy.

INSTRUMENTATION ENGINEERING INTERVIEW QUESTIONS AND ANSWERS(Part-1)

Hello Friends, here i am posting about important interview part 1 questions which are mostly  asked by the all core companies  like HONEYWELL, SOLITONTECH , MAHINDRA SATYAM , L&T etc.  So please make use of it.  All the best!!!

PART 1

QUESTIONS:

1. What are different types of orifice plates? State their uses.
2. How do you identify an orifice in the pipeline?
3. Why is the orifice tab provided?
4. Explain Bernoulli’s theorem. State its application.
5. How can a D.P. transmitter be calibrated?
6. How is flow measured in square root?
7. Name different parts of a pressure gauge. Explain the use of hair spring in the pressure gauge.

ANSWERS:

1. What are different types of orifice plates? State their uses.
Different orifice plates are:
 1. Concentric
 2. Segmental
 3. Eccentric
 Concentric: These plates are used for ideal liquid as well as gases and steam service. Concentric holes are present in these plates, thats why it is known as concentric orifice.
 Segmental: This plate has hole in the form of segment of the circle. This plate is used for colloidal and sherry flow measurement.
 Eccentric: This plate has the eccentric holes. This plate is used in viscous and sherry flow measurement.

2. How do you identify an orifice in the pipeline?
An orifice tab is welded on the orifice plate which extends out of the line giving an indication of the orifice plate.

3.Why is the orifice tab provided?
Following reasons justify for providing orifice tab:
1. Indication of orifice plate in a line
2. The orifice diameter is marked on it.
3. The material of the orifice plate.
4. The tag number of the orifice plate.
5. To mark the inlet of an orifice.

4. Explain Bernoulli’s theorem. State its application?
Bernoulli’s theorem states that the ‘total energy of a liquid flowing from one point to another remains constant’. It is applicable for non-compressible liquids. For different types of liquid flow Bernoulli’s equation changes. There is direct proportion between speed of fluid and its dynamic pressure and its kinetic energy. It can be used in various real life situations like measuring pressure on aircraft wing and calibrating the airspeed indicator. It can also be used to low pressure in the venturi tubes present in carburetor.

5. How can a D.P. transmitter be calibrated?
D.P. transmitter can be calibrated using following steps:
1. Adjust zero of Xmtrs.
2. Perform static pressure test: Give equal pressure on both sides of transmitter. Zero should not shift either side. If the zero shifts then carry out static alignment.
3. Perform vacuum test: Apply equal vacuum to both the sides. Zero should not shift.
4. Calibration procedure: Give 20 psi air supply to the transmitter and vent L.P. side to atmosphere. Connect output of the instrument to the standard test gauge. Adjust zero. Apply required pressure to the high pressure side and adjust the span. Adjust zero gain if necessary.

6. How is flow measured in square root?
Flow varies directly as the square root of pressure. Thus, F=K of square root of applied pressure. Since this flow varies as the square root of differential pressure. The pressure pen does not directly indicate flow. Thus flow can be determined by taking the square root of the pen. Assume the pen reads 50% of the chart. So, flow can be calculated using the pen measure in the chart.

7. Name different parts of a pressure gauge. Explain the use of hair spring in the pressure gauge.
Pressure gauge includes following components:
1. ‘C’ type bourdon tube.

2.  Connecting link3.  Sector gear
4.  Pinion Gear
5.  Hair spring
6.  Pointer
7.  Dial
Use of hair spring: Hair spring is responsible for controlling torque. It is also used to eliminate any play into linkages.

How to Calibrate Your DP Transmitter

To calibrate an instrument involves checking that the output of the given instrument corresponds to given inputs at several points throughout the calibration range of the instrument. For the analog DP transmitter, its output must be calibrated to obtain a zero percent (4mA) to 100 percent (20 mA) output proportional to the DP transmitter’s zero percent to 100 percent range of input pressures.


Calibration: A Technician's Guide (ISA Technician)

In other words calibration of the transmitter is required to make the transmitter’s percent input equal to the transmitter’s percent output. This is accomplished by adjusting screws located and clearly marked as ZERO and SPAN on the analog transmitter’s outer casing. The ZERO and SPAN screws may also be referred to as the ZERO and RANGE adjustment screws for some manufacturers of DP transmitters.   If you got here looking for information on smart transmitter calibration please see : How to Calibrate Smart Transmitters  Whatever the model/manufacturer of your DP transmitter, it can be easily calibrated according to the manufacturers specific instruction on how to calibrate it. For every calibration you need to do, consult your manufacturer’s specific instruction for calibrating the specific DP transmitterHowever there are general guidelines you need to follow before you calibrate any transmitter:

Step 1:

Ensure all the materials needed for the calibration are within reach e.g meters, pressure source, pressure gauge, Digital multimeter, power supply module(24V) etc


Step 2:

Record and put down the following(can easily be sourced from transmitter nameplate): (a) Transmitter make and model (b) Transmitter calibration range (c) Transmitter span (d) Transmitter MWP(Maximum Working Pressure)

Step 3:

Connect all the equipment needed for the calibration exercise in the appropriate manner. To ensure you don’t make any mistake, you should draw a connection diagram for all equipment involved paying particular attention to polarity of transmitter and power source! Then connect them according to your connection diagram. A typical DP cell transmitter calibration diagram is shown below:


For your application, this could be modified slightly. For example if the pressure source is a hand pump, you can easily control the pressure applied to the DP cell. However, if you are doing field calibration that requires the use of the actual process pressure, you will need a pressure regulator in conjunction with a pneumatic calibrator to help you control the pressure applied to the DP cell.


Step 4:

Most transmitter calibration done is a five point calibration. That is for 0%, 25%, 50%, 75% and 100% of input span or range (in this case pressure input into the DP transmitter). This should correspond exactly to 0%, 25%, 50%, 75% and 100% of the transmitter output span (4- 20mA). The graph below illustrates the correlation between input and output values.
Readings are taken for both increasing and decreasing input values and the corresponding transmitter output values are recorded

Step 5:

In most calibration done, you will be doing either a bench(shop) calibration – A bench calibration is a procedure where the device is calibrated at a calibration bench using calibration devices to simulate the process, – or a field calibration where the actual process is used. Whether you are doing a bench calibration or a field calibration, the low port of the DP transmitter cell is vented to the atmosphere(as shown in the connection diagram above) and the high port of the DP transmitter connected to a pressure source e.g a hand pump or any other suitable pressure source in a bench calibration or the actual process pressure through a pressure regulator and a pneumatic calibrator in a field calibration. So once your equipment is well setup, power it up and pressurize the high port of your DP transmitter. Record the current reading in (m A) which will be your first data point. Continue pressurizing the transmitter and recording your readings for the five points (0%, 25%, 50%, 75% and 100% of input pressure). All the reading obtained will be the as found readings. If you calibrate the DP transmitter before first testing and recording the as found data, the history of the device performance data will be lostYou are now ready to calibrate the DP transmitter. Note that during the calibration process, the transmitter’s zero percent, (LRV), is to be calibrated to the , LRV, of the calibration range and the transmitter’s span is to be calibrated to the, URV, of the calibration range. For example, suppose a DP transmitter with output 4 – 20mA is to be used to measure pressure in the range 0 – 300 psig, then the transmitter zero percent (LRV) is 4mA and will be calibrated to 0psig and the transmitter’s 100%, URV, which is 20mA will be calibrated to 300psig. Locate the manufacturer’s instruction manual and with it locate the transmitters ZERO and SPAN adjustment screws sometimes called Zero and Range adjustment screws. Note that these screws each connect to a variable resistance (potentiometer) and can be turned indefinitely. That is the potentiometer is of a type that once fully adjusted clockwise or counter clockwise the screw may continue to turn without further varying the resistance for either direction.                        

The potentiometer has a maximum of 20 turns between minimum and maximum resistance therefore turning the ZERO or SPAN screws clockwise or counter-clockwise for 20 turns will cause the potentiometer to be at either maximum or minimum. Please note that for the analog DP transmitter, the ZERO and SPAN adjustments are interactive. That is, adjusting one has an effect on the other. Specifically, changes made to the span adjustment almost always alter the DP transmitter’s ZERO point. This back and forth adjustment of the ZERO and SPAN is what makes the DP transmitter calibration sometimes tedious.

Step 7:

Turn the ZERO and SPAN screws both 20 turns clockwise. Next turn both screws10 turns counter clockwise to approximately adjust the potentiometer to the mid resistance point (50%).Step 8:Apply the 0% (LRV) pressure to the transmitter’s High side, and the transmitter’s low side vented so that there is no differential pressure acting across the transmitter’s DP cell.Step 9:Adjust the ZERO screw on the transmitter while observing the current meter to cause the indication to be 4m A, which is the transmitters LRV output. This may not be exactly 4mA but depending on your plant’s acceptable margin of error, you should get a value very close to 4mA.Step 10:Next pressurize the high side of the DP transmitter to cause the pressure applied to the high side to increase to the 100 percent value (URV) of the calibration range.   Step 11:Adjust the SPAN screw while observing the meter’s current indication to cause the meter to indicate 20 mA, which is the 100% (URV) output value signal for the DP transmitter.Step 12:100% input to the transmitter (pressure) exactly equals the transmitters 0 % through 100 % output (4 - 20 mA current). A correctly calibrated DP transmitter can be described as one where the % input equals the % output for all values between 0 and 100 percent.                        Once you are satisfied with the level of accuracy of the calibration result, you are done with the calibration of the DP transmitter otherwise you will have to continue fine tuning the calibration process until a reasonable accuracy is achieved.Calibration: A Technician's Guide (ISA Technician)You must understand that for accurate calibration of any instrument including your DP transmitter, the manufacturer’s manual is the ultimate guide towards achieving a very good calibration. The steps outlined above may differ from your manufacturer’s procedure however, they are a good guide.