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Identification and Symbols 11

C H A P T E R 2

IDENTIFICATION AND SYMBOLS

IdentificationUsers of instruments and control systems need some method for identifying equipment so theycan manage the engineering, purchasing, installation, and maintenance of such systems. There-fore, one of the key requirements of measurement and control systems is that every devicehave a unique tag number. An installation’s guidelines for these tag numbers should eitherconform to a company standard or to ISA-5.1-1984 (R1992). Either way, these tag guidelinesshould be uniform throughout the plant.

The practitioner is advised that, per ISA-5.1-1984 (R1992), identification of instruments isaccording to function and not construction. Thus, a differential pressure transmitter across anorifice plate in a flow measuring application would be tagged as “FT,” not “PDT.”

According to the ISA standards, the typical tag number consists of two parts (see figure 2-1):a functional identification and a loop number (e.g., TIC-103). The functional identificationconsists of a first letter (designating the measured or initiating variable; for example, F forFlow, T for Temperature, etc.) and one or more succeeding letters (identifying the functionsperformed; for example, I for Indicating, T for Transmitter, C for Controller, V for Valve,etc.). For example, a temperature indicating controller is identified as TIC, a flow transmitteras FT; a temperature recorder as TR, a level controller as LC, and so on.

Figure 2-1Tag Numbers

The loop number is unique to each loop and is typically common to all instruments within aloop. For example, if in a loop, a transmitter FT is measuring flow, and a controller FC is con-trolling a valve FV, then they would all share the same loop number, that is, FT-123, FC-123,and FV-123. See figure 2-4 for further examples.

The total number of letters in a tag number should not exceed four. Identification letters areshown in table 2-1; typical letter combinations are shown in table 2-2. Both tables are based onISA-5.1-1984 (R1992). For further information, the user should refer to the latest issue of thisISA standard.

EXPANDED TAG NUMBER 10-PAH-5A - Tag Number 10 - Optional Prefix A - Optional Suffix Note: Hyphens are optional as separators

TYPICAL TAG NUMBER TIC 103 - Instrument Identification or Tag Number T 103 - Loop Identification 103 - Loop Number TIC - Functional Identification T - First-letter IC - Succeeding-Letters

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12 The Condensed Handbook of Measurement and Control 3rd Edition

Table 2-1Identification letters.

Notes:

1. To cover unlisted meanings that will be used repetitively. The meanings need be defined only once.

2. To cover unlisted meanings that will be used only once (or used to a limited extent). The meanings must be defined outside the tagging bubble.

3. The grammatical form may be modified as required. Example: “Indicate” may mean “indicator” or “indicating.”

4. A first letter used with a modifier is treated as a first-letter entity. Example: “TDI” for dif-ferential temperature.

NOTE: Numbers in parentheses refer to following explanatory notes.

FIRST-LETTER (4) SUCCEEDING-LETTERS (3)

MEASURED OR

INITIATING

VARIABLE MODIFIER

READOUT OR

PASSIVE

FUNCTION OUTPUT FUNCTION MODIFIER

A Analysis (5,19) Alarm

B Burner, Combustion User's Choice (1) User's Choice (1) User's Choice (1)

C User's Choice (1) Control (13)

D User's Choice (1) Differential (4)

E Voltage Sensor (Primary

Element)

F Flow Rate Ratio (Fraction) (4)

G User's Choice (1) Glass, Viewing

Device (9)

H Hand High (7, 15, 16)

I Current (Electrical) Indicate (10)

J Power Scan (7, 24)

K Time, Time Schedule Time Rate of Change

(4, 21)

Control Station (22)

L Level Light (11) Low (7, 15, 16)

M User's Choice (1) Momentary (4, 25) Middle,

Intermediate (7,15)

N User's Choice (1) User's Choice (1) User's Choice (1) User's Choice (1)

O User's Choice (1) Orifice, Restriction (23)

P Pressure, Vacuum Point (Test)

Connection (26)

Q Quantity Integrate, Totalize (4)

R Radiation Record (17)

S Speed, Frequency Safety (8) Switch (13)

T Temperature Transmit (18)

U Multivariable (6) Multifunction (12) Multifunction (12) Multifunction (12)

V Vibration, Mechanical

Analysis (19)

Valve, Damper,

Louver (13)

W Weight, Force Well

X Unclassified (2) X Axis Unclassified (2) Unclassified (2) Unclassified (2)

Y Event, State or

Presence (20)

Y Axis Relay, Compute,

Convert (13, 14, 18)

Z Position, Dimension Z Axis Driver, Actuator,

Unclassified Final

Control Element



5. To cover all analysis not described by a “user’s choice” letter. The type of analysis must be defined outside the tagging bubble.

6. To be used in lieu of a combination of first letters. Generally used for multipoint record-ers/indicators.

7. Using these modifiers is optional. Example: The letters H and L may be omitted in the undefined case.

8. To cover only emergency protective primary elements, such as a rupture disk (PSE), and emergency protective final control elements, such as a pressure safety valve (PSV).

9. Applies to instruments that provide an uncalibrated view, such as a sight-glass level gage (LG) and television monitors.

10. Normally applies to an analog or digital readout.

11. Used for pilot lights. Example: A running light for a motor may be identified as EL or YL, depending on whether the measured variable is voltage or operating status, respectively. Used also for process indicating light. Example: A high-level light (LLH).

12. Used instead of a combination of other functional letters.

13. Used for hand-actuated switches or on-off controllers. It is incorrect to use the succeeding letters CV for anything other than a self-actuated control valve.

14. Used generally for solenoid devices and relays. For other uses, the meaning needs to be defined outside the tagging bubble.

15. These modifying terms correspond to values of the measured variable, not to values of the signal. Example: A high level from a reverse-acting level transmitter should be LAH.

16. The terms high and low when applied to positions of valves denote open and closed posi-tions, respectively.

17. Applies to any form of permanent storage of information.

18. Used for the term transmitter.

19. Used to perform machine analysis (whereas the letter A performs more general analyses). Except for vibration, the meaning must be defined outside the tagging bubble.

20. Not to be used when control or monitoring responses are time driven or time/schedule driven.

21. To signify a time rate of change of the measured variable. Example: WKIC means a rate-of-weight-loss indicating controller.

22. Used to designate an operator’s control station, such as a manual loading station (HIK), or the operator interface of a distributed control system.

23. Used also to designate a restriction orifice (FO).

24. Used also to designate a temperature-scanning recorder (TJR).

25. Used also to designate a hand momentary switch (HMS).

26. For example, an analysis test point is identified as AP.

These notes are abbreviated. See ISA-5.1-1984 (R1992) for full text.


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Table 2-2Typical letter com

binations

Note: This table is not all-inclusive. Other Possible Combinations:*A, alarm, the annunciating device, may be used in the same FO (Restriction Orifice) PFR (Ratio)fashion as S, switch, the actuating device. FRK, HIK (Control Stations) KQI (Running Time Indicator)

FX (Accessories) QQI (Indicating Counter)**The letters H and L may be omitted in the undefined case. TJR (Scanning Recorder) WKIC (Rate-of-Weight-Loss Controller)

LLH (Pilot Light) HMS (Hand Momentary Switch)

First-Letters

Initiating or Measured Variable

Controllers Readout DevicesSwitches and

Alarm Devices* Transmitters

Solenoids, Relays, Computing Devices

Primary Element

Test Point

Well or Probe

Viewing Device, Glass

Safety Device

Final ElementRecording Indicating Blind

Self-Actuated Control Valves Recording Indicating High** Low Comb Recording Indicating Blind

A Analysis ARC AIC AC AR AI ASH ASL ASHL ART AIT AT AY AE AP AW AV

B Burner/Combustion BRC BIC BC BR BI BSH BSL BSHL BRT BIT BT BY BE BW BG BZ

C User’s Choice

D User’s Choice

E Voltage ERC EIC EC ER EI ESH ESL ESHL ERT EIT ET EY EE EZ

F Flow Rate FRC FIC FC FCV,FICV

FR FI FSH FSL FSHL FRT FIT FT FY FE FP FG FV

FQ Flow Quantity FQRC FQIC FQR FQI FQSH FQSL FQIT FQT FQY FQE FQV

FF Flow Ratio FFRC FFIC FFC FFR FFI FFSH FFSL FE FFV

G User’s Choice

H Hand HIC HC HS HV

I Current IRC IIC IR II ISH ISL ISHL IRT IIT IT IY IE IZ

J Power JRC JIC JR JI JSH JSL JSHL JRT JIT JT JY JE JV

K Time KRC KIC KC KCV KR KI KSH KSL KSHL KRT KIT KT KY KE KV

L Level LRC LIC LC LCV LR LI LSH LSL LSHL LRT LIT LT LY LE LW LG LV

M User’s Choice

N User’s Choice

O User’s Choice

P Pressure/ Vacuum

PRC PIC PC PCV PR PI PSH PSL PSHL PRT PIT PT PY PE PP PSV,PSE

PV

PD Pressure, Differential

PDRC PDIC PDC PDCV PDR PDI PDSH PDSL PDRT PDIT PDT PDY PE PP PDV

Q Quantity QRC QIC QR QI QSH QSL QSHL QRT QIT QT QY QE QZ

R Radiation RRC RIC RC RR RI RSH RSL RSHL RRT RIT RT RY RE RW RZ

S Speed/Frequency SRC SIC SC SCV SR SI SSH SSL SSHL SRT SIT ST SY SE SV

T Temperature TRC TIC TC TCV TR TI TSH TSL TSHL TRT TIT TT TY TE TP TW TSE TV

TD Temperature, Differential

TDRC TDIC TDC TDCV TDR TDI TDSH TDSL TDRT TDIT TDT TDY TE TP TW TDV

U Multivariable UR UI UY UV

V Vibration/Machinery Analysis

VR VI VSH VSL VSHL VRT VIT VT VY VE VZ

W Weight/Force WRC WIC WC WCV WR WI WSH WSL WSHL WRT WIT WT WY WE WZ

WD Weight/Force, Differential

WDRC WDIC WDC WDCV WDR WDI WDSH WDSL WDRT WDIT WDT WDY WE WDZ

X Unclassified

Y Event/State/Presence YIC YC YR YI YSH YSL YT YY YE YZ

Z Position/Dimension ZRC ZIC ZC ZCV ZR ZI ZSH ZSL ZSHL ZRT ZIT ZT ZY ZE ZV

ZD Gaging/Deviation ZDRC ZDIC ZDC ZDCV ZDR ZDI ZDSH ZDSL ZDRT ZDIT ZDT ZDY ZDE ZDV

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Instrument Line SymbolsOn any drawing, symbols should remain consistent throughout the drawing to avoid confusion.Typical line symbols are shown with a lighter-weight line than are process lines.

In identifying an electric signal, the user should choose either the dashed-line symbol or the tri-ple cross-hatch symbol and apply it consistently (the author prefers the dashed-line symbol).On any given set of documents internal consistency is strongly recommended. Instrument linesymbols are shown in figure 2-2 and are taken from ISA-5.1-1984 (R1992).

Figure 2-2Instrument Line Symbols



General Instrument or Function SymbolsGeneral instrument or function symbols identify the location and function of an instrument.They are shown in figure 2-3 and are taken from ISA-5.1-1984 (R1992).

Figure 2-3General instrument or function symbols



Examples of how symbols should be used are shown in figure 2-4. Figure 2-5 shows the degreeof detail typically shown on a diagram.

Figure 2-4aExamples of symbol usage.

TWO INSTRUMENTS SHARING A COMMON HOUSING

F021

RESTRICTION ORIFICE

FG23

FLOW SIGHT GLASS

FE4

FLOW ELEMENT

FI17

VARIABLE AREAFLOW INDICATOR

FT20

FLOW ELEMENT INTEGRAL WITH ELECTRONIC TRANSMITTER

FT107

FSL107

FAL107

FIELD MOUNTED FLOWSWITCH (FSL-107) ACTUATINGLOW-FLOW ALARM (FAL-107)

TO PNEUMATIC VALVE OR OTHER RECEIVER

FIELD MOUNTED MANUALLOADING STATION WITH OUTPUT GAGE

HIC 4 HV

300

HC300

FI402

FT402

FC FE402

MANUAL LOADING STATION (HC-300)WITHOUT OUTPUT GAGE ANDSHARING A COMMON HOUSINGWITH A FLOW RECEIVERINDICATOR (FI-402)

T TA AN NK K

LI9

LEVEL INDICATOR,WITH TWO CONNECTIONS

ELECTRONIC LEVELTRANSMITTER,WITH ONE CONNECTION

LT11

PT106

PRESSURE TRANSMITTERWITH PNEUMATIC OUTPUT



Figure 2-4bExamples of symbol usage.

TE TITI7 8

TEMPERATURE ELEMENTWITH WELL (ELEMENTNOT CONNECTED TO SECONDARY INSTRUMENT)

FILLED-SYSTEM-TYPETEMPERATURE INDICATOR WITH WELL

9

BIMETALLIC-TYPETHERMOMETER, GLASSTHERMOMETER, OR OTHERLOCAL TEMPERATURE INDICATOR

TT101

TIC101

TV101

FC

TEMPERATURE LOOP CONTROL

TSH100

TSL100

TAHL100

COMMON ALARM ANNUNCIATOR FOR HIGH- AND LOW- TEMPERATURE

PI17

PI18

WITH PRESSURE LEAD LINE LINE-MOUNTED

PRESSURE INDICATOR CONNECTED TODIAPHRAGM SEAL WITH FILLED SYSTEM

PI16

PRESSURE INDICATOR, DIRECT-CONNECTED

GAS FLOW

MASSFLOW

FT111

PT108

TT117

FY111

FIC111

FC

FV111

MASS-FLOW COMPUTATION PERFORMED BY MASS-FLOW COMPUTING RELAY FY-111HAVING LINEAR INPUTS FOR PRESSURE AND TEMPERATURE AND A NON-LINEAR INPUT FOR FLOW



Figure 2-4cExamples of symbol usage.

VALVE BODIES AND DAMPERS

GENERAL SYMBOL ANGLE BUTTERFLY ROTARY VALVE

THREE-WAY FOUR-WAY GLOBE

HV3

HAND CONTROL VALVE IN SIGNAL LINE

DIAPHRAGM DAMPER OR LOUVER

FURTHER INFORMATION MAY BE ADDED ADJACENT TO THE BODY SYMBOL EITHER BYNOTE OR CODE NUMBER

BACKPRESSURE REGULATOR,SELF-CONTAINED

PCV5

BACKPRESSURE REGULATOR WITH EXTERNAL PRESSURE TAP

PCV4

PSV7

PRESSURE RELIEF OR SAFETY VALVE,GENERAL SYMBOL

PSE PSE13 14

RUPTURE DISK ORSAFETY HEAD FORPRESSURE RELIEF

RUPTURE DISK ORSAFETY HEAD FOR VACUUM RELIEF


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Figure 2-5E

xample show

ing the degree of detail.

FROM FY-901A

f(t)

FY901B

XFY

901C

HOT OIL

AAHAIC941

FT

FEFV

TE

AT AE

TT900

900900

920

941 941

920

FAHL

X

FC

FY FY900A 900B

HOT OILRETURN

FIC900

TK0818

pH

LT940

FV940

LIC940

LAHL

FC

V3

V1 V2

LV

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