instrumentation

7/21/2019 Instrumentation

http://slidepdf.com/reader/full/instrumentation-56deaa8d800eb 1/11

Report on Instrumentation

1



CONTENT

1. INSTRUMENTATION………………………………………………….....page 3

2. AIR OPERATED CONTROL VALVES……………..……………….....page 3

3. FLUID FLOW MEASUREMENTS………………..………………….....page 5

4. TEMPERARURE MEASUREMENT…..…………………………….....page 7

5. PRESSURE MEASUREMENT …………………..…………………....page 9

. LI!UID MEASUREMENT……………………………………………...page 1"

7. REFERENCES……...…………………………………………………...page 11

FI#URES

F$g%&e 1.1P&e''%&e C()*&(+ A$& Va+,e ………..………….…………………page 4

F$g%&e 1.2 O&$-$e P+a*e I) F+a)ge C())e*$() …. …………………….....page 5

F$g%&e 1.3 R(*a/e*e& ………………………………………………………….page

F$g%&e 1.4 0$/e*a++$ D$a+ Te/pe&a*%&e I)$a*(& ………………………..page

F$g%&e1.5 Te&/((%p+e …………………….…………………………….…page 9

F$g%&e1. 0(%&() T%e …………………….……………………………….page 9

F$g%&e1.7 L$%$ Mea'%&e/e)* …………………….…………………….…page 1"

1. Instrumentation

2



Instruments are devices used to perform 2 main functions in a chemical process.

These functions are those that can be used to control the process at the best

operating conditions and secondly they provide a record of what has happened in

the chemical process.

There are 4 main process operating conditions that are considered as importantvariables used in chemical processes these include;

1.) Flow ate2.) Temperature!.) "ressure #$acuum)4.) %i&uid %evel

Instrumentation system can be used to monitor the process variable present in a

chemical process. The process variable need to be monitored due to the fact that'

any small variation from the prescribed operating conditions may cause poor &uality

product' loss of material' loss of productions and fouling of e&uipment. Therefore

the instruments present in an instrument system can be used for monitoringprocess variable and it can be used to control these variables as well.

Instruments used on a chemical process' must be able to provide records of

operations. This is done to (eep chec(s on operating eciency' yields produced as

well as on production. Therefore it is necessary to calculate daily' how much

material *ows into and out of each process.

In addition to the above mentioned functions. Instruments also provide a local

indication of the process variable which the process controller is able to chec( on as

well as to compare it with the reading on the panel in the control room.

2. Air-Operated Controls Valves

+hen applying the proper procedures' it is easy to see that if a valve could be made

to operate automatically and in accordance with the changes in a certain variable'

this variable can then be controlled automatically as well. ,uch a valve is called an

-ir operated diaphragm control valve/.

The di0erence between an ordinary gate valve and an air operated diaphragm

control valve is as follows;

In an ordinary gate valve' the gate is caused to move up and down by turning the

hand wheel. owever in an air operated diaphragm control valve' the stem of a

motor valve is connected to a rubber disc or diaphragm which is then moved up or

down by the resultant force imparted by air pressure and a balance spring.

!



2.1 Actions Of Air Operated Control Valves;

There are 2 common types of air operated control valves also (nown as pneumatic

actuator control valves these include; air to open diaphragm control valves and air

to close diaphragm control valves.

In summary ontrol valves operated through pneumatic actuators can either be

i.) ir To 3penii.) ir To lose

These valves are designed in such a way that if the air supply fails' the control valve

will either be fully opened or fully closed. owever these actions are determined by

the safety re&uirement of the process for eample if the valve is used to control

steam or fuel *ow; the valve should be shut o0 completely in case of air failure and

therefore the valve should be fully closed. 3n the other hand' if the valve is

handling cooling water to a reactor' the *ow of air should be maimum in case of

emergency and therefore the valve should be fully opened.

Figure 1.1 5 "ressure ontrol ir $alve

4



3. Fluid Flow Measurement

+hen wor(ing with *uids which travel at a variety of speeds' it is important to (eep

trac( of the speed of the *uid used. Therefore on a typical 6T% "lant *uid *ow

measurement devices are used to control and monitor the *ow rate of these li&uids.

The two most common *ow measuring devices used in a 6T% "lant is the ori7ce

"late and the 8i0erential "ressure 9eter.

These devices operate based on the principle that a *uid #6as:%i&uids) *owing

through a constriction in a line will show a pressure drop and that this pressure drop

is proportional to the rate of *ow.

3.1 Orice Meter

The ori7ce meter consists of a circular plate with a circular hole in the center of the

plate. This device is then placed between two *anges in a line this is done to ensure

that a di0erential pressure inside a pipe is created.

The selection of the sie of the ori7ce depends upon the rate of *ow epected to

pass through it. +hich means that the smaller the hole' the greater the pressure

drop across the plate for a given rate of *ow and vice versa. It is therefore

important that the sie of the ori7ce is chosen correctly so that the pressure drop

which is at a maimum epected *ow rate will not eceed the range of the *ow

meter or measuring device.

Figure 1.2 3ri7ce "late In Flange onnection

3.2 !"# Cell

nother type of di0erential measuring device most commonly used' is the

di0erential pressure cell also (nown as a 8::" ell.

The 8:" ell operates on the force balance principle. <esides being used as a

di0erent measuring device' a 8:" ell is also used as a level indicator and can

=



operate level alarms. In this case the di0erential pressure caused by the weight of a

column of li&uid is transmitted to the indicator or it is transmitted to an alarm.

3.3 $otameter

nother type of *ow measuring device is the rotameter. It consists of a tapered

glass tube with metal or plastic bob inside it.

The otameter function by allowing the bob found inside the otameter to rise up

inside the glass tube whenever a *uid *ows inside it. The higher the bob rises in the

glass tube indicates the speed at which the li&uid is *owing through the pipe. "lease

note that the rotameter is structured in such a way that the *owrate inside the pipe

can be read on a scale which is etched onto the glass.

Figure 1.!5 otameter

>



%. &emperature Measurement

The measurement of a substance temperature can be measured by either a Thermometer' .T.8. 3 by use of Thermocouples. ?ample of uses for these

devices includes' chec(ing metal surface temperature and bric(wor( temperature.

<imetallic 8ial Temperature Indicator is an industrial thermometer typically used in

a 6T% "lant. This thermometer is made up of a long' narrow tube containing a

bimetallic element which is connected to a pointer which has a dial mar(ed o0 into

degrees. It is made up of two narrow strips of di0erent metals bonded together. s

the temperature changes' one of strips epand more than the other and the

elements are bent. The amount that the element is de*ected is dependent on the

temperature and so can be calibrated to measure the temperature change. This coil

can then be placed inside a tube and the degree of the coiling of the metal can then

be attached to a pointer with a dial which will then allow the temperature changes

to be read o0 the pointer.

Figure 1.45 <imetallic 8ial Temperature Indicator

@



%.1 $.&.!. '$esistance &(ermo !evice)

esistance Thermo 8evice Is a device that is similar to the bimetallic temperaturedial. This device wor(s by having ! wires wrapped together. It functions on the

principle that temperature change e0ect the electrical resistance of the wires and

the change can then be measured and converted to units of degrees.

%.2 &(ermocouple

Thermocouple device have 2 wires of di0erent metals twisted together at their ends

and this end is then welded closed' this point is referred to as the Aunction point.

The principle of thermocouple is based on the fact that when two unli(e metals are

Aoined' they generate a very small voltage. This voltage generated in the wires is

proportional to the temperature of the Aunction. To use this device the welded Aunction is placed at the point where the temperature is being measured.

The voltage generated by the thermocouple is measured by means of an instrument

called a "otentiometer' where it is calibrated in millivolts and is directly lin(ed to the

measurement at the Aunction eample of thermocouple is the lumel and Bic(el

Thermocouple.

Figure 1.=5 Thermocouple

C



"lease Bote that a thermowell is a device used to get the sensing element i.e. the

thermometer' .T.8 and Thermocouple. s close to the process point as possible.

*. #ressure Measurement

The most convenient and widely used pressure measuring device for industrial

application is the <ourdon Tube "ressure 6auge.

The <ourdon Tube is a thin5walled metal tube of oval shape. This tube is then bent

into an arc of a circle having; 1 end of the tube closed and connected to a pointer

and the other end opened and connected to a vessel: line on which the pressure is

being measured.

pressure is then applied to the inside of the tube' after which the *at sides of thetube then stretches and tend to straighten out the tube. This then causes the

moving of the closed end of the tube to move the lin(age it is connected to. This is

done in order to magnify the movement of the tube and the pressure applied to the

device can then be read o0 a mar(ed dial.

Figure 1.>5 <ourdon Tube

D



>. +i,uid Measurement

The most common device used in li&uid measurement is the gauge glass. 6auge

6lasses: ,ight 6lasses are made up of a transparent tube through which the

operator of a tan( or boiler can observe the level of li&uid contained within a tan(.

,imple 6auge glasses:,ight glasses are made up a plastic or glass tube connected

to the bottom of the tan( at one end and the top of the tan( at the other end. The

level li&uid found within a sight glass is then used to measure the li&uid found inside

the tan(.

Figure 1.@5 %i&uid 9easurement

1E



7. Re-e&e)e'

• Instrumentation By Mr. Ade. S.L (www.slideshow.net)

• Instrumentation By Devidas Bage,Patrik Dalvi,o!esh "hilveri, Aniket

Du!ade (www.slideshow.net)

• "hemi#al Plant $ Module B, %&ISA, Study uide, "'P$B B* +.M. oos

and evised -y M.A. Smith

• &otes rom Ben Marais Basi#s and /undamentals Le#ture Session on

Instrumentation, PetroSA.

11

http://www.slideshow.net/




instrumentation

Documents