Process Instrumentation And Control Pdf

process instrumentation and control pdf

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Source : ourmumbaicity. Handbook for Control Valve Sizing — page not available. Probably many other are in the same situation.

Instrumentation & Control

So far we have just looked at instruments that sense, control, and influence process variables. Transmitters, controllers, and control valves are respective examples of each instrument type.

However, other instruments exist to perform useful functions for us. Quite often process transmitters are not equipped with readouts for whatever variable they measure: they just transmit a standard instrument signal 3 to 15 PSI, 4 to 20 mA, etc.

An indicator gives a human operator a convenient way of seeing what the output of the transmitter is without having to connect test equipment pressure gauge for PSI, ammeter for mA and perform conversion calculations.

Moreover, indicators may be located far from their respective transmitters, providing readouts in locations more convenient than the location of the transmitter itself. An example where remote indication would be practical is shown here, in a nuclear reactor temperature measurement system:.

It would be unsafe for human beings to approach the nuclear reactor when it is in full-power operation, due to the strong radiation flux it emits. There is nothing preventing us from connecting multiple indicators, at multiple locations, to the same 4 to 20 milliamp signal wires coming from the temperature transmitter. This allows us to display the reactor temperature in as many locations as we desire, since there is no absolute limit on how far we may conduct a DC milliamp signal along copper wires.

A numerical-plus-bargraph indicator appears in this next photograph, mounted in the face of a metal panel inside of a control room:. This particular indicator shows the position of a flow-control gate in a wastewater treatment facility, both by numerical value It is directly wired in series with the same milliamp current signal sent to the gate actuator. A less sophisticated style of panel-mounted indicator shows only a numeric display, such as this unit shown here:.

The following photograph shows a field-mounted indicator, operating directly from the electrical power available in the mA loop. The numerical display of this indicator uses LCD technology rather than red-glowing LEDs, in order to use less electrical power:.

Recorders usually have indications built into them for showing the instantaneous value of the instrument signal s simultaneously with the historical values, and for this reason are usually designated as indicating recorders. Paper chart recorders are a form of instrumentation with a long history. Note the circular form of the paper chart, allowing the pen to draw a trace as the circular chart slowly spins.

A padlock on the front glass cover prevents tampering with the chart recording:. A typical chart from one of these recording devices is shown in this illustration, taken from page of the same engineering periodical:. Another design of paper chart recorder is the strip style, using a long strip of paper between two spools one to play out the paper and another to take it up. Like the circular chart recorder design, the strip chart recorder also has a long history.

Pressure drop caused by a burst 4-inch water pipe is also seen on this recording, between PM and PM. Both circular and strip chart recorder designs survive to this day. Two circular chart recorders are shown in the following photograph, used to record temperatures at a powdered milk processing facility:. Two more chart recorders appear in the next photograph, a strip chart recorder on the right and a paperless chart recorder on the left. The strip chart recorder uses a scroll of paper drawn slowly past one or more lateral-moving pens, while the paperless recorder does away with paper entirely by plotting graphic trend lines on a computer screen:.

Recorders are extremely helpful for troubleshooting process control problems. Here, the setpoint SP appears as a perfectly straight red line, the process variable as a slightly erratic blue line, and the controller output as a moderately erratic purple line. We can see from this trend that the controller is doing exactly what it should: holding the process variable value close to setpoint, manipulating the final control element as far as necessary to do so.

The fact that the process variable never deviates significantly from the setpoint tells us the control system is operating quite well. What accounts for the erratic controller output, then? The answer to this question is any factor requiring the controller to change its output in order to maintain the process variable at setpoint.

Variations in process load would account for this: as other variables in the process change over time, the controller is forced to compensate for these variations in order to ensure the process variable does not drift from setpoint.

Referencing our previous example of a steam boiler water level control system, one of these influencing variables is steam demand. A wildly-fluctuating output signal may indicate a problem somewhere else in the process placing undue demands on the control system , but there is certainly no problem with the control system itself: it is doing its job perfectly well.

Here is an example of a trend recording for a process in manual mode, where the process variable response is seen graphed in relation to the controller output as that output is increased and decreased in steps:. This delay is called dead time , and it is generally detrimental to control system performance. Imagine trying to steer an automobile whose front wheels respond to your input at the steering wheel only after a 5-second delay!

This would be a very challenging car to drive. The same problem plagues any industrial control system with a time lag between the final control element and the transmitter.

Typical causes of this problem include transport delay where there is a physical delay resulting from transit time of a process medium from the point of control to the point of measurement and mechanical problems in the final control element. This next example shows another type of problem revealed by a trend recording during manual-mode testing:. Here, we see the process quickly responding to all step-changes in controller output except for those involving a change in direction. This problem is usually caused by mechanical friction in the final control element e.

Sometimes it becomes useful to temporarily place a recorder into an instrumentation system for diagnostic purposes. Another type of instrument commonly seen in measurement and control systems is the process switch. The purpose of a switch is to turn on and off with varying process conditions. Usually, switches are used to activate alarms to alert human operators to take special action.

In other situations, switches are directly used as control devices. If this switch activates, something has gone wrong with the compressor control system, and the high pressure alarm PAH, or pressure alarm, high activates to notify a human operator. All three switches in this air compressor control system are directly actuated by the air pressure in the vessel: in other words, these are direct process-sensing switches.

For example, the chlorine wastewater disinfection system shown earlier may be equipped with a couple of electronic alarm switches to alert an operator if the chlorine concentration ever exceeds pre-determined high or low limits:.

Note how the diagram shows these two alarm units connected to the electronic mA signal output by the chlorine analyzer AT. Since both alarms work off the 4 to 20 milliamp electronic signal output by the chlorine analytical transmitter AT rather than directly sensing the process, their construction is greatly simplified.

If these were process-sensing switches, each one would have to be equipped with the analytical capability of directly sensing chlorine concentration in water. In other words, each switch would have to be its own self-contained chlorine concentration analyzer, with all the attendant complexity. In addition to providing alarm capability, this SPA module also provides a digital display a small LCD screen to show the analog signal value for operational or diagnostic purposes.

Some of the alarm types provided by this unit include high process, low process, out-of-range, and high rate-of-change. In a similar manner, we may add pressure-actuated process alarm switches to pneumatic PSI signal lines coming from pneumatic transmitters to add alarm capability to a system designed for continuous measurement. Even though the physical stimulus actuating each switch is an air pressure , the switches still serve the purpose of liquid level alarm signaling because that air pressure is an analogue representation of water level in the steam drum.

In other words, these two alarm switches LSL and LSH indirectly sense water level by monitoring the pneumatic signal pressure output by the level transmitter LT. The alternative to pressure-actuated water level alarm switches would be independent level-sensing switches attached directly to the steam drum, each switch equipped with its own means of directly sensing water level:.

If that one transmitter were to fail, all three system functions would be compromised. This elevates the importance of a single instrument, which is generally not desirable from the perspective of reliability and process safety.

In the system where each level alarm switch independently senses steam drum water level, one device may fail without compromising either of the other two functions. The final determination should be based on a rigorous analysis of device versus system reliability, which is typically the task of a process engineer.

Process alarm switches may be used to trigger a special type of indicator device known as an annunciator. The indicator light does not turn off until the actual alarm condition the process switch has returned to its regular state.

This photograph shows an annunciator located on a control panel for a large engine-driven pump. Each white plastic square with writing on it is a translucent pane covering a small light bulb. When an alarm condition occurs, the respective light bulb flashes, causing the translucent white plastic to glow, highlighting to the operator which alarm is active:. Opening the front panel of this annunciator reveals modular relay units controlling the blinking and acknowledgment latch functions, one for each alarm light:.

This modular design allows each alarm channel to be serviced without necessarily interrupting the function of the other channels in the annunciator panel. A simple logic gate circuit illustrates the acknowledgment latching feature here implemented by an S-R latch circuit common to all process alarm annunciators:.

Time logging is of particular importance in the process industries, as the sequence of events is often extremely important in investigations following an abnormal operating condition. Knowing what happened, and exactly when it happened is much more informative than simply knowing which alarms have tripped. Don't have an Control account? Create one now. Forgot your password? Click here. Latest Projects Education.

I - Fundamentals Vol. II - Instrumentation Vol. III - Measurement Vol. IV - Control Vol. V - Reference Worksheets. An example where remote indication would be practical is shown here, in a nuclear reactor temperature measurement system: It would be unsafe for human beings to approach the nuclear reactor when it is in full-power operation, due to the strong radiation flux it emits. A numerical-plus-bargraph indicator appears in this next photograph, mounted in the face of a metal panel inside of a control room: This particular indicator shows the position of a flow-control gate in a wastewater treatment facility, both by numerical value Two circular chart recorders are shown in the following photograph, used to record temperatures at a powdered milk processing facility: Two more chart recorders appear in the next photograph, a strip chart recorder on the right and a paperless chart recorder on the left.

The strip chart recorder uses a scroll of paper drawn slowly past one or more lateral-moving pens, while the paperless recorder does away with paper entirely by plotting graphic trend lines on a computer screen: Recorders are extremely helpful for troubleshooting process control problems.

This next example shows another type of problem revealed by a trend recording during manual-mode testing: Here, we see the process quickly responding to all step-changes in controller output except for those involving a change in direction.

Process switches and alarms Another type of instrument commonly seen in measurement and control systems is the process switch. Opening the front panel of this annunciator reveals modular relay units controlling the blinking and acknowledgment latch functions, one for each alarm light: This modular design allows each alarm channel to be serviced without necessarily interrupting the function of the other channels in the annunciator panel.

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Indicators, Recorders, Process Switches and Alarms

Box Richfield, Ohio Ph: Veteran- Owned manufacturers' representative agency serving the process instrumentation and hazardous area electrical and automation industries on a continuing basis within Ohio for over 24 years. The Coriolis meter identifies flow rate by directly measuring fluid mass over a wide range of temperatures with a high degree of accuracy. Badger Product Overview: click here for catalog pdf. Dynasonics Product Overview: click here for catalog pdf. Pulsar Product Overview: click here for catalog pdf.

Our goal is to introduce the Process Control Instrumentation used in theindustry. Since its foundation by Mr. Felix Mateo in the 50th, our Company was well known to be pioneer in using the most advanced technologies in its products. Acquisition of 8 analog variables, 8 logic variablesand 8 alarm logic outputs Local Display of reading, channel n, alarms and other parameters Remote Control of logic actuators Alarm-loops associated to the analog inputs 2 counters with reset, inhibition and preset functions Inputs and ranges configurable in Pt , Input and output of analog variables and logicsignals in remote control systems m Remote control of actuators Accuracy 0.

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A Brief History & Future of Process Instrumentation

Book Detail: Instrumentation and Process Control. Outlines of Dairy: Technology. Module 1: Instruments and measurement system Lesson 1. Functions of instruments and measurement system Lesson 2. Elements of generalized measurement system.

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Fundamentals of Industrial Instrumentation and Process Control

Instrumentation & Control Process Control Fundamentals

Instrumentation is a collective term for measuring instruments that are used for indicating, measuring and recording physical quantities. The term has its origins in the art and science of scientific instrument-making. Instrumentation can refer to devices as simple as direct-reading thermometers , or as complex as multi-sensor components of industrial control systems. Today, instruments can be found in laboratories, refineries, factories and vehicles, as well as in everyday household use e. Elements of industrial instrumentation have long histories. Scales for comparing weights and simple pointers to indicate position are ancient technologies.

So far we have just looked at instruments that sense, control, and influence process variables. Transmitters, controllers, and control valves are respective examples of each instrument type. However, other instruments exist to perform useful functions for us. Quite often process transmitters are not equipped with readouts for whatever variable they measure: they just transmit a standard instrument signal 3 to 15 PSI, 4 to 20 mA, etc. An indicator gives a human operator a convenient way of seeing what the output of the transmitter is without having to connect test equipment pressure gauge for PSI, ammeter for mA and perform conversion calculations.

Instrumentation

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Instrumentation Basics: Measurement Terminology.

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