SAMA Diagram

Process and Instrument Diagram - Process Equipment

Process and Instrument Diagrams - Flow Measuring Devices

Process and Instrument Diagrams- Valve Failure Mode

Process and Instrument Diagrams- Valve Actuator Types

Process and Instrument Diagrams- Process Valve

Process and Instrument Diagrams- Instrument Bubbles

Process and Instrument Diagrams- Line Connection

Process and Instrument Diagrams- Line Types

SAMA Diagrams- IV

Rectangular blocks such as the , P, I, and D shown in this diagram represent automatic
functions. Diamond-shaped blocks such as the A and T blocks are manual functions which must
be set by a human operator. Showing even more detail, the following SAMA diagram indicates the
presence of setpoint tracking in the controller algorithm, a feature that forces the setpoint value to
equal the process variable value any time the controller is in manual mode:

Here we see a new type of line: dashed instead of solid. This too has meaning in the world of SAMA diagrams. Solid lines represent analog (continuously variable) signals such as process variable, setpoint, and manipulated variable. Dashed lines represent discrete (on/off) signal paths, in this case the auto/manual state of the controller commanding the PID algorithm to get its setpoint either from the operator’s input (A) or from the process variable input (the flow transmitter: FT).

SAMA Diagrams-III

SAMA diagrams may show varying degrees of detail about the control strategies they document.
For example, you may see the auto/manual controls represented as separate entities in a SAMA
diagram, apart from the basic PID controller function. In the following example, we see a transfer
block (T) and two manual adjustment blocks (A) providing a human operator the ability to
separately adjust the controller’s setpoint and output (manipulated) variables, and to transfer
between automatic and manual modes:

SAMA Diagrams- II

A cascaded control system, where the output of one controller acts as the setpoint for another
controller to follow, appears in SAMA diagram form like this:

In this case, the primary controller senses the level in a vessel, commanding the secondary (flow)
controller to maintain the necessary amount of flow either in or out of the vessel as needed to
maintain level at some setpoint.

SAMA Diagrams - I

SAMA is an acronym standing for Scientific Apparatus Makers Association, referring to a unique
form of diagram used primary in the power generation industry to document control strategies.
These diagrams focus on the flow of information within a control system rather than on the process
piping or instrument interconnections (wires, tubes, etc.). The general flow of a SAMA diagram is
top-to-bottom, with the process sensing instrument (transmitter) located at the top and the final
control element (valve or variable-speed motor) located at the bottom. No attempt is made to
arrange symbols in a SAMA diagram to correlate with actual equipment layout: these diagrams are
all about the algorithms used to make control decisions, and nothing more.

A sample SAMA diagram appears here, showing a flow transmitter (FT) sending a process
variable signal to a PID controller, which then sends a manipulated variable signal to a flow control
valve (FCV):

Concept of Motor and Generator

This is very useful, as we can use to convey energy from one place to another, using metal wires as conduits for this energy. This is the basic idea behind electric power systems: a source of power (a generator ) is turned by some mechanical engine (windmill, water turbine, steam engine, etc.), creating an electric potential. This potential is then used to motivate free electrons inside the metal wires to drift in a common direction. The electron drift is conveyed in a circuit through long wires, where they can do useful work at a load device.

Given the proper metal alloys, the friction that electrons experience within the metal wires may
be made very small, allowing nearly all the energy to be expended at the load (motor), with very little
wasted along the path (wires). This makes electricity the most efficient means of energy transport
known.The electric currents common in electric power lines may range from hundreds to thousands of
amperes. The currents conveyed through power receptacles in your home typically are no more than 15 or 20 amperes.

Key Design Components of Final Control Elements

A final control element is the device manipulated by a control loop to affect the process, principally by means of changing a flow. Final control elements are an essential part of nearly every process control system. Without final control elements, there is no way of controlling the process. We could not change operating points or correct for disturbances. There may be several layers of control loops, but it is usually a flow that a final control element ends up changing in a process. The most notable exceptions are heater or electrode current and mixer speed.

By far, the most common final control element is the control valve, with its attendant positioner, actuator, and other components. Variable speed peristaltic pumps are used for the exceptionally small flows of bench top and pilot plant operations. Variable speed positive displacement pumps are used for small additive and reagent flows in production. For large flows in plants and powerhouses, variable frequency drives and dampers are sometimes used instead of control valves to reduce capital and operating costs.

Axial and centrifugal blowers, fans, and pumps are used for the flow ranges normally associated with gas and liquid streams in industrial plants. A variable frequency drive (VFD), particularly in large utility flow applications, can save energy by the elimination of a control valve and its pressure drop. However, the energy savings is usually overestimated for process streams by not taking into account the service time and efficiency at low flow and the loss in turndown due to static head.

A damper can reduce the cost of the final element or fit in a non-circular duct. Dampers are commonly used in HVAC systems, boilers, furnaces, and scrubbers to manipulate air and vent gas flows. Dampers have a lower pressure drop than a control valve, but generally the performance (e.g., rangeability, resolution, sensitivity, speed, and seal) of a damper is not as good as a control valve. The leakage and limited dynamic response and materials/ruggedness of construction of dampers relegate their application to mostly utility and vent systems.

Valve design, dynamics

The shaft of the actuator and the stem of the internal closure component (plug, ball, or disk) of the control valve are normally separate. The closure component may be cast and forged with the stem or the stem may be connected during valve assembly. The actuator shaft moves the stem that moves the closure component. (While “shaft” and “stem” are more appropriate terms for the actuator and the closure component, respectively, in practice the terms “stem” and “shaft” are used interchangeably.) The amount of play (looseness or gap) in the connections between the shaft, stem, and closure component is backlash that creates deadband and determines, in part, how well the valve will respond to small changes in signal. Excessive seal friction of a closure component that is rotated (e.g., ball or disk) can result in shaft windup. The location and type of connection of the positioner feedback mechanism for valve travel determines whether the positioner is seeing the response of just the actuator or the actual response of the closure component.

Previous methods of testing valve response involved making much larger changes in the valve signal than would normally be made in closed loop control. Most valves will look OK with these large changes in requested position. In service, the change in controller output from scan to scan is generally small (e.g., < 0.2%), except during the start of an operation or process. For small changes in valve signals, the resolution limit from sticktion and deadband from backlash that prevent a good response and create a sustained oscillation (limit cycle) are observable. Current test methods established by the ISA-75.25.01-2000 (R2006) standard address the effect of step size on response.

Control valves with excessive sticktion, backlash, and shaft windup can actually increase process variability when the loop is in automatic by the creation of oscillations from the continuous hunting of integral action to find a position it cannot attain exactly.

Smart digital positioners with a good closure component measurement have the sensitivity and tuning options to mitigate the consequences of stick-slip and backlash by fast feedback control. Built-in diagnostics can pinpoint problems such as packing friction besides monitoring the dynamic response of the valve. 

Sliding stem (globe) valves have the least amount of deadband because of the direct connection between the actuator shaft and trim stem, and low trim friction. For rotary valves, connections can be problematic since there is the need to convert the linear motion of a piston or diaphragm shaft to rotary motion and the changes in the effective lever arm length. Rotary valves originally designed by piping valve manufacturers for on-off or manual operation often have a non-representative position measurement and a degree of excessive backlash and shaft windup that cannot be corrected by a positioner.

Valve best practices

For best performance, users should consider the following during the specification of control valves:

• Actuator, valve, and positioner package from a control valve manufacturer
• Digital positioner tuned for valve package and application
• Diaphragm actuators where application permits (large valves and high pressure drops may require piston actuators)
• Sliding stem (globe) valves where size and fluid permit (large flows and slurries may require rotary valves)
• Low stem packing friction
• Low sealing and seating friction of the closure components
• Booster(s) on positioner output(s) for large valves on fast loops (e.g., compressor anti-surge control)
• Online diagnostics and step response tests for small changes in signal
• Dynamic reset limiting using digital positioner feedback

VFD cable problems

Belden Inc. has studied the radiated noise from cables between the VFD and the motor. Unshielded VFD cables can radiate 80V noise to unshielded communication cables and 10V noise to shielded instrument cables. The radiated noise from foil tape shielded VFD cables is also excessive. A foil braided shield and armored cable performs much better. Still, a spacing of at least one foot is recommended between shielded VFD and shielded instrumentation cables. The cables should never cross. As a best practice, separate trays to isolate VFD and instrumentation cables should be used to avoid mistakes during plant expansions and instrumentation system upgrades.

VFD turndown

Since the inverter waveform is not purely sinusoidal, it is important to select motors that are designed for inverter use. These “inverter duty” motors have windings with a higher temperature rating (Class F). Another option that facilitates operation at lower speeds to achieve the maximum rangeability offered by a pulse width modulation (PWM) drive is a higher service factor (e.g., 1.15).

The turndown of a VFD could drop to 4:1 for the following systems:

• Older VFD technologies such as 6-step voltage (excessive slip at low speed)
• Systems with a high static head (flow plummets to zero at a low speed)
• Operation on the flat portion of the prime mover curve (cycling at low speed)
• Hot gases (motor overheats at a low speed)

VFD controls

The turndown (rangeability) of a VFD can be increased by ensuring the pump head is large compared to the static head, by using PWM inverters, and by dealing with the heating problems at low speeds. Turndown also depends upon the control strategy in the variable frequency drive.

Which is faster: A valve or VFD?

Exceptionally fast loops can ramp off-scale in milliseconds. These loops have essentially a zero process dead time and may have a high process gain due to a narrow control range (e.g., fractional inches of water column for furnace pressure). These loops require DCS scan times of 0.05 to 0.1 seconds. Special fast scan rate digital controllers or analog controllers are needed. DCS scan time requirements of 0.2 seconds or less signify a VFD opportunity. A properly designed VFD has no measureable dead time, while control valves and dampers take anywhere from 0.2 to 2.0 seconds to start to move. For example, an incinerator pressure and polymer pressure loop that could get into trouble in less than 0.1 second required a VFD and analog controller to stay within the desired control band.

A VFD has a negligible response time delay unless a deadband or dead zone is introduced into the drive electronics to slow response to process measurement noise, or if a low resolution input card is used. A control valve or damper has a dead time proportional to the resolution limit (e.g., from stiction and windup) and dead band (from backlash and windup) divided by the rate of change of the process controller output. For large or fast changes in signal, this dead time disappears.

VFD best practices

With a VFD, a tachometer or inferential speed feedback signal should be sent to the process controller in the DCS that is sending the signal to the drive. The speed feedback should be used in a similar way to the position feedback from a digital positioner to prevent the process controller output from changing faster than the VFD can respond. The use of the dynamic reset limit option for the loops in the DCS can automatically prevent the process controller from outrunning the response of any type of final element. For best performance, users should consider the following during the specification and implementation of variable frequency drive systems:

• High resolution input cards
• Pump head well above static head on-off valves for isolation
• Design B TEFC motors with class F insulation and 1.15 service factor
• Larger motor frame size
• XPLE (cross-linked polyethylene) jacketed foil/braided or armored shielded cables
• Separate trays for instrumentation and VFD cables
• Inverter chokes and isolation transformers
• Ceramic bearing insulation
• Pulse width modulated inverters
• Properly set deadband and velocity limiting in the drive electronics
• Drive control strategy to meet rangeability/speed regulation requirements
• Dynamic reset limiting using inferential speed or tachometer feedback

*The Article is from InTech.

ABB Positioner Commissioning

Step 1 - Unscrew the screws of Positioner.

Step 2 - There will be four Hard Buttons and one LCD Display.

Step 3 - The Hard buttons are for Mode, Up, Down and Enter.

Step 4 – Press Up+Down+Enter Hard buttons together. As soon as LCD will display P1.0 Unpress Enter. P1.0 should be set as per Condition (Linear/Rotary). After setting Condition Unpress Up+Down. The LCD will display 1…2…3…

Step 5 – Press Mode+Enter+Up Hard buttons together. Continuously Press Up button. As soon as LCD will display P11.0 is Inactive. Now, Unpress Mode+Enter.

Step 6 – Press Enter Button until LCD Display 1…2…3… P11.0 is active that will be displayed in LCD.

Step 7 – Press Mode+Up P11.1 for FS Load Function and Enter the Hard Button. The LCD will display Complete and will display 1…2…3...

Step 8 – Press Mode+Down P11.0 shows active and then press Enter and make it Inactive and further LCD displays 1…2…3..

Step 9 –  Press Mode+Up and keep on pressing Up until P11.3 is not displayed when it is displayed configure in NV save .Press Enter that will LCD Display 1…2…3…(Position Sense)

Step 10 – Press Mode+Up until it will show Manual in Display. Then Press Down Button continuously to change the present value to 0. Then further press Up continuously to make present value 75(Valve Open and Close Accordingly in Manual).

Step 11 – Press Enter+Up+Down will display P1.0 and as soon as the LCD shows unpress Enter button.P1.0 is linear. LCD will display 1….2…3….

Step 12 – Press Mode+Up LCD will display P1.1, Press Enter LCD will display 1…2…3… the Positioner will automatically run for Calibration. The LCD will display 10...20...40... …200 and LCD will Display complete.

·         Step 10 – Manual Calibration

·         Step 12 – Auto Calibration.                                 

Pressure Switches- II

The below photograph shows two pressure switches sensing the same fluid pressure as an
electronic pressure transmitter:

A legacy design of pressure switch uses a bourdon tube as the pressure-sensing element, and a
glass bulb partially filled with mercury as the electrical switching element. When applied pressure
causes the bourdon tube to flex sufficiently, the glass bulb tilts far enough to cause the mercury
to fall against a pair of electrodes, thus completing an electrical circuit. A great many pressure
switches of this design were sold under the brand name of “Mercoid,” with a few appearing in this
photograph of a steam boiler (the round-shaped units with glass covers allowing inspection of the
bourdon tube and mercury tilt switch):

Pressure Switches- I

A pressure switch is one detecting the presence of fluid pressure. Pressure switches often use
diaphragms or bellows as the pressure-sensing element, the motion of which actuates one or more
switch contacts.
The “normal” status of a switch is the condition of minimum stimulus. A pressure
switch will be in its “normal” status when it senses minimum pressure (e.g. n applied pressure, or
in some cases a vacuum condition).If the trip setting of a pressure switch is below atmospheric pressure, then it will be “actuated” at atmospheric pressure and in its “normal” status only when the pressure falls below that trip point (i.e. a vacuum).

Proximity Switches

A proximity switch is one detecting the proximity (closeness) of some object. By definition, these
switches are non-contact sensors, using magnetic, electric, or optical means to sense the proximity
of objects.The “normal” status of a switch is the condition of minimum stimulus. A proximity
switch will be in its “normal” status when it is distant from any actuating object.

Being non-contact in nature, proximity switches are often used instead of direct-contact limit
switches for the same purpose of detecting the position of a machine part, with the advantage of
never wearing out over time due to repeated physical contact. However, the greater complexity (and
cost) of a proximity switch over a mechanical limit switch relegates their use to applications where
lack of physical contact yields tangible benefits.

Most proximity switches are active in design.They incorporate a powered electronic circuit to sense the proximity of an object. Inductive proximity switches sense the presence of metallic objects through the use of a high-frequency magnetic field. Capacitive proximity switches sense the presence of non metallic objects through the use of a high-frequency electric field. Optical
switches detect the interruption of a light beam by an object.

The schematic diagram symbol for a proximity switch with mechanical contacts is the same as
for a mechanical limit switch, except the switch symbol is enclosed by a diamond shape, indicating
a powered (active) device:

Many proximity switches, though, do not provide “dry contact” outputs. Instead, their output
elements are transistors configured either to source current or sink current. The terms “sourcing”
and “sinking” are best understood by visualizing electric current in the direction of conventional
flow rather than electron flow.


The following schematic diagrams contrast the two modes of switch operation, using red arrows
to show the direction of current (conventional flow notation). In both examples, the load being
driven by each proximity switch is a light-emitting diode (LED):

Limit Switches

A limit switch detects the physical motion of an object by direct contact with that object.
An example of a limit switch is the switch detecting the open position of an automobile door,
automatically energizing the cabin light when the door opens.The “normal” status of a switch is the condition of minimum stimulus. A limit switch will be in its “normal” status when it is not in contact with anything (i.e. nothing touching the switch actuator mechanism).

Limit switches find many uses in industry, particular in robotic control and CNC (Computer
Numerical Control) machine tool systems. In many motion-control systems, the moving elements
have “home” positions where the computer assigns a position value of zero. For example, the axis
controls on a CNC machine tool such as a lathe or mill all return to their “home” positions upon
start-up, so the computer can know with confidence the starting locations of each piece. These home
positions are detected by means of limit switches. The computer commands each servo motor to
travel fully in one direction until a limit switch on each axis trips. The position counter for each
axis resets to zero as soon as the respective limit switch detects that the home position has been
reached.

A typical limit switch design uses a roller-tipped lever to make contact with the moving part.
Screw terminals on the switch body provide connection points with the NC and NO contacts inside
the switch. Most limit switches of this design share a “common” terminal between the NC and NO
contacts like this:

Hand Switch

A hand switch is an electrical switch actuated by a person’s hand motion. These may take the form of toggle, push button, rotary, pull-chain, etc. A common form of industrial push button switch looks something like this:

The threaded neck inserts through a hole cut into a metal or plastic panel, with a matching nut
to hold it in place. Thus, the button faces the human operator(s) while the switch contacts reside
on the other side of the panel.

When pressed, the downward motion of the actuator breaks the electrical bridge between the
two NC contacts, forming a new bridge between the NO contacts:

The schematic diagram symbol for this type of switch looks much like the real thing, with the
normally-closed contact set on top and the normally-open contact set below:

Temperature Switch

A temperature switch is one detecting the temperature of an object or Atmosphere at times. Temperature switches often use bimetallic strips as the pressure-sensing element, the motion of which actuates one or more contacts(which can be a switch).
The “normal” status of a switch is the condition of minimum stimulus. A temperature switch will be in its “normal” status when it senses minimum temperature

If the trip setting of a temperature switch is below ambient temperature, then it will be “actuated” at ambient temperature and in its “normal” status only when the temperature falls below that trip point (i.e. colder than ambient).

Some Useful Conversions

Conversion formula for temperature

• oF = (oC)(9/5) + 32
• oC = (oF - 32)(5/9)
• oR = oF + 459.67
• K = oC + 273.15

Conversion factors for distance

1 inch (in) = 2.540000 centimeter (cm)
1 foot (ft) = 12 inches (in)
1 yard (yd) = 3 feet (ft)
1 mile (mi) = 5280 feet (ft)

1.3.3 Conversion factors for volume
1 gallon (gal) = 231.0 cubic inches (in3) = 4 quarts (qt) = 8 pints (pt) = 128 fluid ounces (fl. oz.)
= 3.7854 liters (l)
1 milliliter (ml) = 1 cubic centimeter (cm3)

Conversion factors for velocity

1 mile per hour (mi/h) = 88 feet per minute (ft/m) = 1.46667 feet per second (ft/s) = 1.60934
kilometer per hour (km/h) = 0.44704 meter per second (m/s) = 0.868976 knot (knot – international)

Conversion factors for mass

1 pound (lbm) = 0.45359 kilogram (kg) = 0.031081 slugs
1.3.6 Conversion factors for force
1 pound-force (lbf) = 4.44822 newton (N)
1.3.7 Conversion factors for area
1 acre = 43560 square feet (ft2) = 4840 square yards (yd2) = 4046.86 square meters (m2)
1.3.8 Conversion factors for pressure (either all gauge or all absolute)
1 pound per square inch (PSI) = 2.03603 inches of mercury (in. Hg) = 27.6807 inches of water (in.
W.C.) = 6.894757 kilo-pascals (kPa)

Conversion factors for pressure (absolute pressure units only)

1 atmosphere (Atm) = 14.7 pounds per square inch absolute (PSIA) = 760 millimeters of mercury
absolute (mmHgA) = 760 torr (torr) = 1.01325 bar (bar)
1.3.10 Conversion factors for energy or work
1 British thermal unit (Btu – “International Table”) = 251.996 calories (cal – “International Table”)
= 1055.06 joules (J) = 1055.06 watt-seconds (W-s) = 0.293071 watt-hour (W-hr) = 1.05506 x 1010
ergs (erg) = 778.169 foot-pound-force (ft-lbf)

Conversion factors for power

1 horsepower (hp – 550 ft-lbf/s) = 745.7 watts (W) = 2544.43 British thermal units per hour
(Btu/hr) = 0.0760181 boiler horsepower (hp – boiler)

Terrestrial constants

Acceleration of gravity at sea level = 9.806650 meters per second per second (m/s2) = 32.1740 feet
per second per second (ft/s2)
Atmospheric pressure = 14.7 pounds per square inch absolute (PSIA) = 760 millimeters of mercury
absolute (mmHgA) = 760 torr (torr) = 1.01325 bar (bar)
Atmospheric gas concentrations:
• Nitrogen = 78.084 %
• Oxygen = 20.946 %
• Argon = 0.934 %
• Carbon Dioxide (CO2) = 0.033 %
• Neon = 18.18 ppm
• Helium = 5.24 ppm
• Methane (CH4) = 2 ppm
• Krypton = 1.14 ppm
• Hydrogen = 0.5 ppm
• Nitrous Oxide (N2O) = 0.5 ppm
• Xenon = 0.087 ppm
Density of dry air at 20oC and 760 torr = 1.204 mg/cm3 = 1.204 kg/m3 = 0.075 lb/ft3 = 0.00235
slugs/ft3
Absolute viscosity of dry air at 20oC and 760 torr = 0.018 centipoise (cp) = 1.8 × 10−5 Pascalseconds
(Pa·s)

Process Control System information at your fingertips

Consol Energy, a publicly owned Pittsburgh-based producer of coal and natural gas, is one of the leading diversified energy companies in the U.S. Due to their various operations, they have a vastly distributed control system network. Multiple remote SCADA/HMI branches all connect back to a main control center in Claypool Hills, Virginia. They were experiencing a problem with blind spots (i.e., areas of their process they did not have vision into). This included the operator’s HMI screens at any number of their remote stations. Frequent SCADA/HMI-related problems caused a great deal of time to be put into supporting these remote operations over the phone or making frequent site visits to these extremely remote locations. The time and manpower required to support this kind of remote application was significant.

One such site was a gas processing facility in West Virginia, the next state over. The entire remote processing system was operated by a skeleton crew. The data from the remote location was sent back to the main control center in Virginia, but it did not provide enough information to properly troubleshoot and find the root cause of issues.

Visual confirmation of operator activity

Consol Energy decided to implement a video management system that included the capability to record operator consoles. The console recorder is a software module that enables automatic recording of the HMI or SCADA operator’s console display. With this tool, Longwatch archives exactly what the operator was seeing, because it records the video that is being sent to the display itself. Playing back what the operator was seeing proved to be a very valuable method for troubleshooting, training, and process improvement.

The recorder software provides access to live and recorded video of the operator’s screens. In this way, the control room in Virginia can have access to exactly what the remote operator’s screens look like at any given point in time. Managers can view their operator’s screens live or go back in time to any point to see what the screen looked like in the past.

The operator’s console should be looked upon as an asset, just like an important piece of equipment or part of your process. Consol Energy is now able to troubleshoot issues in real time or find out why an operator did not acknowledge an alarm. Was it due to operator error or did the HMI screen malfunction?

Remote emergency management

After the success of the console recording approach, Consol Energy wanted to add visual monitoring of their remote assets. At the same plant where the operator’s consoles were being recorded, Class I Division 2 cameras were put in place to monitor critical, potentially hazardous areas of their manufacturing process. When emergency situations arise, there is a need to determine the whereabouts of site personnel and also establish which part of the plant is affected.  The Class I Division 2 pan-tilt-zoom cameras provide remote “eyes” necessary to accurately assess the situation.

Consol Energy now has complete vision into their remote applications. The advanced video management system deployed provides video from operator screens along with video from hazardous area cameras that can be viewed anywhere on their network.

*The Article is from InTech

Securing and monitoring a crude oil pipeline

In January of 2011, the Pipeline and Hazardous Materials Safety Administration (PHMSA) invoked a requirement for Chevron to secure and monitor their remote block valve sites for pipeline leaks. PHMSA is a U.S. Department of Transportation agency that develops and enforces regulations for the safe, reliable, and environmentally sound operation of the nation’s 2.6-million mile pipeline transportation system and the nearly one million daily shipments of hazardous materials by land, sea, and air. Pipeline leaks can have a devastating cost in terms of lost production and cleanup effort, not to mention the environmental impact.

Chevron began investigating the options for security, monitoring, and leak detection. Their initial investigation included technologies ranging from 24-hour manned surveillance to radioactive isotope tracers for leak detection. After the evaluation, they decided on a remote video monitoring solution that included advanced video management software and a new hazardous area thermal sensor.

Chevron utilized an advanced video management solution that included the following system components:

• Control Room: Video control center software for integration of video into operator SCADA/HMI screens.
• Remote Site:  Remote DVR appliance for on-site recording, alarming, and direct communication to the PLC.
• Cameras:
  • Thermal imaging camera for pipeline leak detection
  • Pan-tilt-zoom camera for overall site surveillance

A new type of sensor

The solution provided integrates a thermal imaging used to detect hydrocarbon leaks and spills. The camera is optimized for persistent, 24-hour leak detection in locations where pipes rise above ground. The camera is used to detect thermal anomalies present when fluid or high-pressure gaseous leaks occur. The system provides spill detection over the full range of temperature conditions.

Smarter and faster alarm verification

When the thermal camera senses a leak detection event, it immediately alerts the PLC at the remote site via Modbus TCP. The PLC will then send a prioritized alarm message back to the control center. The Longwatch video engine simultaneously records a ten-second video clip surrounding the leak event. This snippet of video is sent over the control network back to the operator’s console. The operator now has the ability to have more information about the event in the form of video. This allows smarter and faster decision-making and gives the operator the information needed to respond to the event appropriately.

*The Article is from InTech

Signal Ranges - Graphical Interpretation

A helpful illustration in understanding analog signal ranges is to consider the signal
range to be expressed as a length on a number line. 

For example, the common 4-20 mA analog current signal range would appear as such:

If one were to ask the percentage corresponding to a 14.4 mA signal on a 4-20 mA range, it
would be as simple as determining the length of a line segment stretching from the 4 mA mark to
the 14.4 mA mark:

As a percentage, this thick line is 10.4 mA long (the distance between 14.4 mA and 4 mA) over
a total (possible) length of 16 mA (the total span between 20 mA and 4 mA). Thus:

This same “number line” approach may be used to visualize any conversion from one analog scale
to another. Consider the case of an electronic pressure transmitter calibrated to a pressure range of
-5 to +25 PSI, having an (obsolete) current signal output range of 10 to 50 mA. The appropriate
current signal value for an applied pressure of +12 PSI would be represented on the number line as
such:

Finding the “length” of this line segment in units of milliamps is as simple as setting up a proportion between the length of the line in units of PSI over the total (span) in PSI, to the length of the line in units of mA over the total (span) in mA:

Solving for the unknown (?) current by cross-multiplication and division yields a value of 22.67
mA. Of course, this value of 22.67 mA only tells us the length of the line segment on the number
line; it does not directly tell us the current signal value. To find that, we must add the “live zero”
offset of 10 mA, for a final result of 32.67 mA.

Thus, an applied pressure of +12 PSI to this transmitter should result in a 32.67 mA output
signal.