Working Principles in Animation
Instrumentation working principles describe how industrial instruments measure, control, and monitor process variables like pressure, flow, temperature, and level. Using animations and clear visuals, this guide explains each instrument’s operation step by step for easy understanding by students and engineers.
Displacer type level transmitter work on principle of Buoyancy, weight of the displacer reduces as the level in the chamber increases. Strain gauge will sense full weight of displacer when chamber is empty.
Picture below shows the look of displacer type level transmitter
Displacer type level transmitter & Strain Gauge. Credit Essam Hakam
Load Cell : load cell is a force transducer. It converts force i.e. tension, compression, pressure, or torque into electrical signal. As force on load cell increases, the electrical signal changes proportionally.
Vortex flowmeters are suitable for measuring the flow of liquid, gas, or steam. sensor is often a piezoelectric crystal, which produces a small, but measurable, voltage pulse every time a vortex is created. Bluff Body(obstacle) causes vortices to be formed, frequency of vortices is proportional to flow rate, these vortices are sensed by sensor above by shedder bar.
Advantages The Advantages of a vortex meter are many. They are summarised below: • No moving parts to wear • No routine maintenance required • Can be used for liquids, gases, and steam • Stable long-term accuracy and repeatability • Lower cost of installation than traditional orifice-type meters • Available in a wide variety of temperature ranges from -185°C to roughly 425°C • Bar-like bluff design allows particulates to pass through without getting clogged • Available for a wide variety of pipe sizes • Available in a wide variety of communication protocols
DisAdvantage: Vortex meters are not a good choice for very low fluid velocities and are not recommended for velocities below approximately 9 cm/sec. At flow rates this low, the vortices are not strong enough to be measured accurately
Installations require a minimum straight run pipe length of 10 to 20 pipe diameters upstream and 5 to 10 pipe diameters downstream depending on the pipe configuration
Maintenance
No routine Maintenance
Over time, the meter shedder bar will erode from process flow. When this happens, flow measure will drift or become erratic. If measurement is suspect, the flow transmitter should be removed and the shedder bar inspected and replaced if needed
. In most cases, a signal failure indicates module failure.
Troubleshooting
No display visible and no output signals present 1. Check supply voltage. 2. Verify that there is no moisture in the termination compartment. 3. Check for blown fuses or damaged wires. 4. Electronics are defective. Replace with appropriate board.
No display signal but output signals are present 1. Check for proper ribbon cable connection from amplifier board to the display module. 2. Display module defective. Replace with appropriate board. 3. Electronics defective. Replace with appropriate board.
Measure value indicated on the local display but no signal output at the current or pulse output 1. Check low flow cut out for proper adjustment. 2. Check flowmeter status to verify that meter has not “failed low” (low flow). 3. Electronics board is defective. Replace with appropriate board
Flowmeter indicates flow when there is no flow: Check LFC, 2. Check for excessive vibration
Flowmeter output increases with flow, but suddenly goes to 4 mA as it approaches full flow: Replace Barrier
Coriolis Mass Flow Transmitter
Principles of Operation: As the mass of a fluid passes through a U-shaped tube, the force causes the tube to swing and twist
Mass is proportional to amount of force applied to the tube. Therefore, the mass flow can be measured by counting the frequency of the vibrations caused by the Coriolis effect. Depending on the size of the mass flowmeter, these vibrations can range from 80 per second to 1000 per second.
a drive coil energizes two magnetic pickoff coils
These pickoffs create an electrical frequency equivalent to the vibration of the tubes caused by the Coriolis effect on the tubes
Advantage: Coriolis meter performs best in liquid service with high flow rates. It measures mass flow, density, and temperature simultaneously. In addition, volumetric flow can be determiined from these parameters. It is capable of a high degree of accuracy, up to ±0.1%. For this reason, Coriolis meters are often used in the transfer of high value products.
Engineers must use caution when selecting a Coriolis meter for gas or vapour service, because the reduced mass may cause the meter to operate in the lower part of the flow range, where accuracy is sacrificed. Other constraints are: • Creates a large pressure drop in gas or vapour service • When measuring liquids, no gas or bubbles can be present • When measuring a gas no liquid may be present • Pipeline vibration can cause problems during operation
coils and RTD inside the element are electrically connected to the core processor.
Maintenance: Coriolis meter element does not require any maintenance.
Zero Calibration To perform a zero Calibration the element must be at normal operating temperature, and full of process fluid. Block in the flow meter downstream, verify there is no flow. Wait until the PV stabilizes. Use your communication device to access the Calibration mode, and select Auto Zero, the transmitter will calibrate automatically. While the transmitter is calibrating the LED on the local display will turn red. When the Calibration is complete, the LED will turn green.
Density Calibration To perform a density Calibration you must have a low-density fluid and a high-density fluid. You may use air and water. Fill the element completely full with the low-density fluid, and block in the transmitter downstream. Use your communication device to access the Calibration menu, and select Density Cal, then select D1 Calibration. Follow the prompts to complete the low-density Calibration. The LED will indicate when the Calibration begins and ends, just as in the zero Calibration. When the low-density Calibration is complete, fill the element with the high-density fluid. Use your communication device to select D2 Calibration, and follow the prompts. The LED will indicate when the Calibration is complete. Empty the high-density liquid from the element, and return the transmitter to service.
core processor counts the electrical pulse created by the pickoffs in the element, and reads the temperature from the RTD
Troubleshooting:
If the LED is red, there is a problem with one of the components in the device. Connect a communication device to the transmitter to access the menu. Look for the Status alarm Use the trouble shooting section in the manuals to look up the Status alarm codes. In the User Manual for the element, there is a list of resistance readings for the coil, pickoffs, and the RTD. If all the resistance readings are close to the ones in the manual, you should run one more test.
put one test lead on the outer case of the element, and the other lead on one of the wires coming out of the element, and test for continuity. Continue to test each wire individually for continuity with the outer case; the meter should indicate an open circuit. If you get any resistance reading at all, between one of the wires and the outer case, the element is shorted to the case, and will have to be replaced.
most accurate type of flow meter for measuring liquids in the upper flow range.
Three main components, the transmitter, the core processor, and the sensor, or element
Ultrasonic Flow Transmitter
two types Doppler Effect & Transient time.
time between sound intervals is called the transit-time. The transit-time of the ultrasonic wave is an indication of velocity. Time-transit meters work well with clean liquids with a laminar flow, or gasses that reflect sound waves.
Doppler effect is the measure of sound wave frequency verses distance
Ultrasonic flow transmitters that use the Doppler effect bounce the waves off particles traveling in the fluid. . Doppler effect meters require a liquid that contains solid particle, bubbles, or turbulence that give the waves something to reflect off. This technology also works on gasses that reflect sound waves
Advantages: Out of pipe installation, No pressure drop, Low maintenance, because there are no moving parts
DisAdvantages: Transit-time meters do not work well with slurries or liquids that have particles traveling in them. • Doppler effect meters do not work well with clean liquids with a laminar flow. • Doppler effect meters have an accuracy of only about 2%. • Obstructions can create false echoes.
Maintenance: Transducer cables should be inspected for cracks or damage to the insulation, and the electronics should be kept clean and dry.
Calibration: There is no sensor Calibration for an ultrasonic flowmeter. The reading is affected by the configuration. If the correct parameters have been entered, it will read correctly. The low flow cut-off can be adjusted if the meter shows a flow when there is not one.
Troubleshooting: Troubleshooting should begin with checking to see if the transmitter has power to it, and inspecting cables
Check error codes in manual.
space between sound intervals in an ultrasonic flowmeter called- Transit-time
Magnetic Flow Transmitter(Emerson 8700)
As per Faraday’s law of electromagnetic induction, conductor that passes through a magnetic field will produce a voltage proportional to the velocity of the conductor. Two electrodes pass through the insulator, and contact the fluid. As the conductive fluid passes the coils, it creates a voltage. The voltage is conducted by the electrodes to the transmitter.
Advantages:
The Advantages of an electromagnetic flow meter are: • Unobtrusive • No pressure drop in the process fluid • Unaffected by environmental changes • Unaffected by changes in pressure viscosity or density • Can measure forward or reverse flow
DisAdvantages: Conductivity of the process fluid must be 5 microsiemens per cubic meter minimum
process fluid must be free of bubbles.
mag meter requires 5 times the pipe diameter of straight pipe before, and 2 times the pipe.
Maintenance: electronics should be kept clean and dry. The housing and conduit should be inspected periodically.
Calibration: Mag meters can be calibrated for zero by blocking in the pipeline downstream while the flow tube is full of fluid, then use the communicator to put the transmitter in Auto Zero mode. Ask operator to close downstream valve
Troubleshooting:
Troubleshooting should begin with checking to see if the transmitter has power. Check error codes, check grounding.
Calibration Procedure: Accept job request
2. Receive required paperwork.
3. Use the correct PPE
4. Explain any precautions required.
5. Inform operations regarding the loop type. Controller to be in manual if meter is part of a control loop or in override if it is a safeguarding loop.
6. Confirm with area operator.
7.confirm instrument tag number in the field before starting work.
8. Visually inspect all instruments, installation, line-up of the loop to be tested as well as other nearby instrumentation.
9. Ensure that power supply is OK.
10. Carry out a loop check.
11. Terminals should not be corroded.
12. Check internal wiring of the amplifier.
13. All wiring should be properly connected to terminals.
14. Check all configurations.
15. If a problem still occurs, the problem could be internal and the meter has to be removed for cleaning or sensor/shedder bar needs replacement.
16. Inform operations job is completed and normalize the system. 17. Sign off required paperwork.
Before proceeding with the function check, if the vortex meter is part of a control loop or a safeguarding loop, what should you do? Put in manual & put back in Auto/Cascade once work done.
Differential Pressure Flow Transmitter
Differential Pressure Transmitter measures “Difference In Pressure” across pressure element i.e. Orifice, Ventury Tube, Flow Nozzle etc. Flow rate is proportional to square root of differential pressure. Thus measuring differential pressure can help us in measuring flow rate. Q α √(ΔP/ρ)
Flame Detector: Flame detector for the detection of a fire in a fire alarm system • Flame scanner for monitoring the condition of a flame in a burner
Principles of Operation: flame eye is used to ensure that a flame is present so that the burner control system can allow the ignition or continued burning of combustible fuels. Flame eyes are designed to detect an actual flame and not the surrounding hot surfaces. If no flame is detected, the burner control system prevents the main gas valve from opening or shuts the main gas and pilot valves if operating.
methods to detect a burner flame: Ultraviolet radiation (UV), IR, Visible light and variations (VL, CCTV, CCTV/IR3 )
Emission of Radiation:
Fire also releases a vast amount of heat energy (infrared). Relatively little UV energy and visible light energy is emitted
non-hydrocarbon fire (for example hydrogen) does not show a CO2 peak. during the burning of hydrogen no CO2 is released.
This “flicker” characteristic is present in varying magnitude and frequency, in all radiating bodies in a furnace environment, but is sufficiently greater in most flames, allowing them to be distinguished from secondary heat sources.
Heat Radiation:
All objects emit energy and, at temperatures as low as 300°K (27°C), radiated heat can be a problem for infrared flame detectors with a very high sensitivity. Dual or multi-channel infrared detectors suppress the effects of heat radiation by means of sensors, which detect just off the CO2 peak frequency, for example 4.1 µm
general rule of thumb is that the mounting height of the flame detector should be twice as high as the highest object in the field of view (such as burner assemblies).
Square Law: flame detector can detect a fire with an area (A) at a certain distance, then a flame area 4 times larger
UV Detection: Ultraviolet (UV) detectors work with wavelengths shorter than 300 nm. These detectors detect flame events within 3 milliseconds to 4 milliseconds due to the UV radiation emitted at the instant of their ignition. UV sources such as lightning, arc welding, radiation, and arcs emitted by pilot igniters can trigger false alarms. In order to reduce false alarms a time delay is often included in the UV Flame detector design.
Troubleshooting: Get area operator to carry out a gas test. 8. Clean the glass eye, removing any dust, ash, or dirt.
To check the alignment, check the power supply to the flame eye. The voltage should be 240 VAC. 12. Install a jumper on the output contact. Have the operator light the burner 13. Look at the flame shape; it should not be distorted or unstable. Have the operator adjust the flame as needed to improve the flame. 14. Make sure the flame eye shutter is functioning. Try to hear it for shutter movement if possible. You can also check the free movement of the shutter when the scanner is disconnected and isolated completely
Combustion: Fire Triangle Heat- O2- Fuel
O2- During some maintenance procedures, an inert gas such as nitrogen may be used to displace the oxygen in order to reduce the risk of fire or explosion. Displacing the oxygen removes the oxygen leg from the fire triangle
Fuel Leg: Area Classification
Heat leg: electrical and non-electrical. combustion engines, welding and grinding activities, metal against metal sparks, and smoking. Only Intrinsic type instrument is allowed in Zone 1.
Fuel Characteristics:
Combustion of a liquid occurs when flammable vapours are released from its surface and they ignite. The amount of flammable vapour given off from a liquid will depend largely on the: • Temperature of the liquid • Ability of the liquid to vaporise • Amount of liquid surface exposed • Length of time the liquid surface is exposed • Air movement over the surface.
Flammable: flash point between 22°C and 55°C, (e.g., diesel, paraffin, oils).
Highly Flammable: flash point of less than 21°C, which generally give off an ignitable vapour without being heated (e.g., petroleum spirit).
Extremely Flammable: (LPG), such as propane, butane, methane, etc.).
Flash Point: Flash point is the minimum temperature where enough vapours can evaporate from a liquid to form a flammable atmosphere in air. Hydrogen -256°C(Its extremely flammable but due to light weight it doesn’t get time to get burnt & escape upwards in atmosphere.
Propane -104°C, Paraffin 38°C
Explosive Limits: For combustion to occur, the ratio of vapour and air must be within a defined range of proportional limits. These limits are known as the lower explosive limit (LEL)(below it very less gas, too much air, doesn’t burn) and the upper explosive limit (UEL)(above it too much gas, less air. Doesn’t burn)
Ignition Temperature: Ignition temperature (sometimes referred to as fire point) is the minimum temperature where combustion can start and continue to burn even after removal of the heat source that ignited the fire. Combustion can occur spontaneously without an actual arc or spark when materials exceed their ignition temperature.
Ignition Energy = Voltage x Current x Time
0.017 mWS of energy will ignite a flammable atmosphere of hydrogen.
Sources of ignition:
Electrical: voltmeters and insulation resistance testers, are a potential source of electrical sparks. Only use these instruments under controlled circumstances, i.e., under the control of a work permit and LEL tests to ensure gas-free conditions.
Hot Surfaces: lighting fixtures, motor starters, switches, and motors may operate with increased temperatures on their exterior surfaces. An overloaded motor with an incorrectly set thermal overload device may produce a surface temperature hot enough to ignite hazardous atmospheres
Batteries: Short-circuited circuits powered by automotive type batteries can generate current levels as high as 1000 amps. In addition to their arcing potential, lead-acid batteries, during charging cycles, will release hydrogen and oxygen gases that can create an explosive atmosphere. This is why battery rooms utilizing this type of battery require ventilation. Some portable electric instruments require low power batteries, if used in hazardous areas. The use of high-power batteries in the same equipment may jeopardize its area certification rating. Only perform battery replacement in a non-hazardous area and always replace with the manufactures recommended batteries
Friction: Grinding, drilling, hammering
Static Electricity: movement of fluids can also generate electrostatic charges, such as a non-conductive liquid flowing through a filter screen. Flow at the nozzle of an aerosol canister may generate up to 5000 V and the nozzle of high-pressure steam cleaning equipment may generate up to 10000 V.
Solutions:
Use brass hammers instead of iron hammers to reduce the possibility of sparks
aluminium and rusty iron or steel is a possible source of ignition known as thermite action. Do not use aluminium ladders in hazardous areas and remember that aluminium paint in hazardous areas also requires caution.
Continuous Grade (Zone 0) A release which is continuous or for long periods, more than 1000 hours per year
Primary Grade (Zone 1) A release which may occur either regularly or at random times during normal operation for considerable periods between 10 hours to 1000 hours per year
Secondary Grade (Zone 2) A release which is unlikely in normal operating conditions and in any event it occurs is only for a short time, less than 10 hours per year A grade of release is considered from the location or source at which a flammable gas, vapour or liquid may be released into the atmosphere
Welded pipe joint Non Hazardous • Area above liquid in a closed tank Zone 0 • Pump gland Zone 1 • Flanged pipe joint Zone 2
Materials that rise in the atmosphere, such as hydrogen, can collect in roof spaces.
Heavier vapours with a density >1, such as butane or propane, may collect in locations lower than ground level, such as holes and pits, and never disperse. They can also drift along at ground level, possibly into an area classified non-hazardous
Zone 0 inst must be intrinsic safe.
Inside tank Zone 0, Above tank vent & inside boundary wall Zone 1, outside tank boundary wall Zone 2.
NEC classification: Class 1 Denotes areas where flammable gas, vapour, or liquid is present
Class 2 Denotes areas where combustible dust is present
Class 3 Denotes areas where ignitable fibres are present
Division 1 Flammable or combustible atmospheres exist under normal operating conditions or have a high likelihood of presence. Division 2 Flammable or combustible atmospheres may exist under abnormal operating conditions or have a low likelihood of presence.
Combustible Dust IEC Zone 20 Zone 21 Zone 22 NEC Class 2 Division 1 Class 2 Division 2
Standard Description IEC International Electrotechnical Commission NEC National Electrical Code (United States) CEC Canadian Electrical Code
Ex designation indicates that the instrument equipment has been constructed and tested for use in an explosive atmosphere
Ex d- Flameproof, Ex ia- Intrinsic safe (Zone 0), ib- zone 1,2, ic-zone2
T5 temperature rating of 100°C is calculated with rated ambient temperature of the equipment (standard rated ambient temperature is 40°C.) and an anticipated temperature rise of 60°C
T3 max 200°C, T6 max 85°C
IP 1st Digit IP 2nd Digit (6- Dust tight),(5- Protected against water projected in jets from any direction, 6- Protected against water projected in powerful jets from any direction, 7- Protected against temporary immersion in water) IP 67
Safety Barrier : The Zener diode limits the voltage to a value referred to as open circuit voltage. The fuse will blow when the diode conducts. This interrupts the circuit, which prevents the diode from burning and allowing excess voltage to reach the hazardous area.
Process
Measuring unit • Controlling unit • Correcting unit
Pressure can be measured at any location in a vessel containing only gas, as pressure is exerted by gas equally in all directions. For a vessel containing liquid, hydrostatic head acts to increase pressure from top to bottom.
Because of the compressibility of gases, their flow is more often expressed in mass units, whereas liquid flows are more often expressed in units of volume
most widely used types of flow measuring devices are: • Differential pressure meters • Rotameter • Positive displacement meters • Turbine meters
controller counters the deviation with an output signal, called the manipulated value (MV) that it transmits to the correcting unit.
movement of the bellows is controlled by the measurement signal (0.2 bar to 1.0 bar) from the process variable.
When the opposing forces of the spring and the bellows are equal, there is no movement of the flapper, which is connected between them. When there is a difference between the opposing forces, an error signal is produced causing the flapper to move either toward or away from the nozzle. In this way, the process measurement is compared with the setpoint to produce a movement of the flapper
movement of the flapper against the nozzle varies the output signal according to the error signal.
electrical equivalent of a throttling valve is a variable resistor, variable speed drive, or another type of device to control a variable speed motor.
Process lag • Measurement lag • Transmission lag • Response lag
degree of accuracy of any process control system can be maximized by minimizing these lags.
Process Lag- heat exchanger will not rise to 300°C immediately after steam flow increases.
interval from the time a final control element change occurs to the time the process variable begins to change is called “dead time.”
Transmission Lag- interval between signal transmissions from detecting element to the arrival of the controller output signal response at the final control element
Distances between the instruments in the loop • Size of the pneumatic tubing • Signal pressure
Response lag- arrivals of the signal to the control valve until the control valve responds to the signal with actual movement.
there will be some dead time before the temperature at the sensing element begins to decrease
Measurement lags are greatest in temperature sensing devices and less significant in flow, level, and pressure measuring devices.
Transmission lag is usually more significant in pneumatic control loops than in electronic control loops
small input to the controller produces a large output
P.B < 100% is narrow band every 1% change in input, there is a 2% change in output.
A narrow proportional band can reduce the amount of “offset” in a control loop. Offset is defined as a sustained difference between setpoint and measured value created by the proportional action when trying to correct an upset in the process
wide proportional band can reduce the amount of cycling in a process control system
With a PB of 100%, a 20 cm (20%) change in tank level will cause the valve plug to move 2 cm (20%) to keep the level at the setpoint value. Using a 50% PB, the valve plug will now move 4 cm when the tank level changes 20 cm. With 200% PB, the valve plug will move 1 cm with a 20 cm level change.
Reset (Integral) Action Reset action (also known as integral action) adjusts the output of a proportional controller to eliminate the offset
Reset is generally expressed in terms of “minutes per repeat” (mpr)
repeats per minute indicate the number of times per minute that the proportional action is applied to the controller output
(PI) controller has no offset. The disAdvantage, however, is a longer period of oscillation and a longer time required the oscillation to cease.
rate action “anticipates” the potential magnitude of a disturbance and takes corrective action before the full change occurs. It does this by measuring the rate of change of the PV deviation (with respect to time) and generates a controller output that is proportional to this rate of change. When the process is at setpoint (and not changing), there is no rate action
When the input signal to a proportional-plus-rate controller changes, the controller measures the speed of the change and produces an instant “boost” to the proportional output signal. In effect, this control action opposes changes in the input and “tries” to stop changes as soon as they are detected. When the input stops changing, the rate contribution to the control action stops, leaving only the proportional part of the controller output, as shown in the following figure
(BMS) for the heater provides semi-automatic operation that requires the operator to initiate a start sequence and to reset/restart the unit after a safety shutdown. The BMS also provides start-up and shutdown sequencing, a status and annunciation display, heater interlock monitoring, emergency shutdown capabilities, and remote control interface signals
Triconex Fault Tolerant Controller
safety features include power failure interlock logic, an emergency shutdown (ESD) pushbutton, a watchdog timer, and an erroneous flame detection system.
Upon power failure, the BMS output power will be lost, all of the outputs will be de-energized, all the burners and pilots will be shut down, the fuel train is blocked in, and the fuel gas vents are opened.
ESD pushbutton or a watchdog timer activates the ESD/Master Control Relay (MCR) system. shutdown valves close regardless of the condition of the logic in the PLC
watchdog timer monitors an output from the PLC that toggles periodically as determined by the PLC program. If this output stops toggling, the watchdog timer times out and trips the MCR.
Erroneous Flame Detection Anytime a flame is detected when there should not be one, the local control panel and the BMS panel cannot be reset, and the start sequence will not be permitted to start.
No single system fault will affect the process.
second fault in line with an existing fault may then initiate a safe trip sequence. Triconex System Alarm is to alert maintenance personnel of the fault. On-Line replacement of the module without any special tools or programming is allowed.
power module has built in diagnostic circuitry which checks for out-of-range voltages and over-temperature conditions. A short on a leg disables the power regulator rather than affecting the power bus
Triconex provides 2 Mbytes of SRAM for User written program control logic, the SOE data, the I/O data, and the diagnostics and communication buffers
three main processors (MP’s)
TMR controller is designed to continue operation after failures. These failures may occur in an input leg, in a main processor, or in an output leg
A dedicated I/O communication (IOC) processor on each main processor manages the data exchange between the MP’s and their corresponding I/O module processor leg. A triplicated I/O bus
each input module is polled
Sequence of Operation
all of the gas flow valves closed. These valves should not be operable until at least two pilots are confirmed on. If less than two burners are lit, the BMS software logic will shut down the heater:
- Verify Valve Position and Check for Leaks
- Heater Reset
- Heater Purge
- Pilot Fuel Valve Line-up and Ignition
- Burner Fuel Valve Line-up
Check for misalignment of the relay gasket. 11. Clean the nozzle. 12. Check the air supply filter regulator for water accumulation. Blow out any water if necessary
. Ensure the air supply is set at 1.4 bar (20.0 psi)
Verify the measurement indicator arm and the measurement link are at a right angle.
Ctrl valve Overhaul- Use SEAT RING REMOVER to remove seat ring, Replace the packing parts.
Reliability
IPS( Instrumented Protected System)
Process safety reviews • Hazard and operability (HAZOP) study • Layer of Protection Analysis • Cause and effect matrices
functionalities of IPSs may be documented in the piping and instrumentation diagrams (P&ID), the instrument logic diagrams (ILD), and cause and effect (C&E) diagrams
Operational override • Maintenance override
Combustion Limits
Fuel/air ratio is within proper limits. • Ignition source with adequate temperature and energy is present
Lower explosibility limit (LEL) is 4% gas in the air supply. • Upper explosibility limit (UEL) is 10% gas in the air supply. To prevent unburned fuel from entering the furnace, the fuel/air ratio must be within the explosibility limits and must be ignited. Combustion is possible only within the explosibility limits.
Safe Firing: 1. furnace must first be purged with air, an inert gas, or steam. Before lighting the (first) burner, the firing chamber must be checked for the presence of an explosive mixture.
Before supplying fuel to the burner, adequate combustion air availability should be checked. 5. The fuel should have a homogeneous composition. If not, the amount of air needed will vary, and the mixture will be too rich or too poor in oxygen. 6. If ignition does not occur within a safe time limit, it must be possible to turn off the fuel supply completely.
fuel supply must be shut off completely if the fuel supply is interrupted. 10. If flame failure occurs or the auto safety devices fail, it must be possible to shut off the fuel supply to the burner within a safe interval.
Safeguarding Requirements during Operation
Full Flame
Minimum and Maximum Gas Pressure
Combustion Air Supply
Level of Fuel Gas Knockout Drum: Liquefied fuel gas must be prevented from entering the furnace through the burner. Liquid entering the burner supplies excessive fuel, exceeding the UEL. This stops combustion and allows unburned fuel to enter the furnace. Subsequent rapid vaporization of the liquid leads to a very hazardous condition, especially if the combustion chamber swings from fuel-rich to air-rich.
Integral windup: when integral is too much & process doesn’t settle, it will keep integrating & loose control. solution to this problem is to configure the master controller with a limit to stop integral action when the high limit relay engages.
6 Safety System during Operation: Flame is extinguished. 2. Heating gas pressure is too low. 3. Combustion airflow is insufficient. 4. Furnace supply flow is too low. 5. Emergency button is pressed. 6. Electrical power supply fails. 7. Instrument air fails. 8. Knockout drum level is high
Ultrasonic Level Transmitter
Principle of Operation:
Tank Gauging System
Vibrating Level Switch: Forks are vibrated by device, when fluid level touches the forks, vibration frequency reduces.
Signal Quality Metrics Technology:
Capacitance Level Transmitter: Capacitance changes as the level increases in the tank.
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