GB/T 2625-1981 PDF in English
GB/T 2625-1981 (GB/T2625-1981, GBT 2625-1981, GBT2625-1981)
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Process detection and controlflow chart. Symbols and letter codes
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Standards related to (historical): GB/T 2625-1981
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GB/T 2625-1981: PDF in English (GBT 2625-1981) GB 2625-1981 (GB/T 2625-1981)
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
GB 2625-81
Process Detection and Control Flow Chart
Symbols and Letter Codes
ISSUED ON: APRIL 1, 1981
IMPLEMENTED ON: MARCH 1, 1982
Issued by: National Bureau of Standards
Table of Contents
1. Introduction ... 4
2. Definitions ... 4
3. Symbols ... 6
4 Letter Codes ... 16
Appendix 1 ... 25
Appendix 2 ... 55
Process Detection and Control Flow Chart
Symbols and Letter Codes
1. Introduction
1.1 This standard is applicable to chemical industry, petroleum industry,
metallurgical industry, electricity industry, light industry, textile industry, building
materials industry and other industries. It aims at specifying unified representation
method for the instrument devices used in process detection and control flow chart.
The symbols and letter codes specified in this standard may also be used in other
design and technical documents.
1.2 The mark of instrument device is composed of symbols and letter codes.
1.3 All departments may put forward supplementary provisions under the condition
that requirements of this standard are not violated.
2. Definitions
For the purposes of this standard, the following definitions apply.
2.1 Process
It refers to any operation or a series of operations that can change energy status,
composition, dimension or other characteristics defined by the data available.
2.2 Function
It refers to the purpose and actions achieved by instruments.
2.3 Loop
It refers to the combination of one or more relevant instruments used for
measuring and (or) controlling process variables.
2.4 Ballon
It refers to the circular symbol used to indicate instrument or instrument mark.
2.5 Point of measurement
It refers to the point at which process variable may be measured.
2.6 Test point
It refers to the test joint to which instruments are not permanently connected and
it is used for connecting instruments temporarily, intermittently or in future.
2.7 Detecting element, sensor, primary element
It refers to the element responding to the value of measured variable directly and
converting measured variable to the form suitable for measurement.
2.8 Transmitter
It refers to the instrument which receives measured variable with the help of
○3 The significance expressed by the subsequent letters may be noun, verb or adjective. For example, "1"
may be indicator, indication or indicated and "T" may be transmitter, transmission or transmitting.
○4 One of the modifier letters of the first letter "d" (difference),"f" (ratio) , "q" (integral, accumulation)
constitutes another significance of measured variable by combining with the letter of measured variable (or
initial variable), thus it shall be considered as one letter. For example: TdI and TI respectively are
temperature difference indication and temperature indication.
Modification letter shall be lowercase. It may also be capital when there is no confusion.
○5 The first letter "A" (analysis) includes the analysis items not specified in Table 13. When it is necessary
to indicate the specific analysis items, "A" is still written in ballon and the analysis items are written in the
upward side outside the circle. For example, "H2" shall be written in the upward side outside the circle and
"A" in circle is unable to be superseded by "H2"
○6 The first letter "U" (multivariable) is used to supersede multiple letters expressing measured variable (or
initial variable), namely "U" is used to express multivariable.
○7 Subsequent letter "U" (multifunction) is used to supersede multiple letters expressing function, namely
"U" is used to express multifunction.
○8 "I" (indication) is only applicable to the reading of actual measurement. It is not applicable to the ruler
without the measured quantity input and only for the manual regulating variable.
○9 See definition (2.18 and 2.1) for the difference between L (light) and A (alarm).
If the light is a part of the circuit, then L shall be used by combining with the first letter. For example, the
pilot light of instruction time cycle shall be KL.
If the light is not a part of the circuit, "L" may be marked individually, and it may also be combined with
the first letter of one selected measured variable in accordance with above-mentioned method. For example,
the running light of electromotor may be assumed that the voltage is its measured variable and marked as
EL; or it is assumed as triggered by the auxiliary electrical contacts of motor starter and marked as XL.
○10 The subsequent letters C (control), S (switch), V (valve) and Y (relay) shall be correctly differed and
selected.
Switch, relay, step-type controller and control valve are able to connect, disconnect or convert one or
more lines.
Control valve is used to control process fluid. Switch, relay, and step-type controller shall not be used to
connect, disconnect or convert the fluid line.
Switch (S) is manually operated.
Automatic and the first device in the circuit is switch (S) or step-type controller and switch (S) is
generally used for alarm pilot light, selection, interlocking or safety; but step-type controller (C) is generally
used for normal operation control.
Automatic but not the first such device in the circuit (for example, operated by switch or step-type
controller) is relay (Y). Relay includes computing instrument, signal converter, selector and amplifier etc.
(see definition 2.9).
○11 The subsequent letter shall be written in accordance with the following sequence:
I R C T Q S A
○12 When the instrument is equipped with indication and recording functions at the same time, R (record) is
the only one letter code to be written and I (indication) needs not to be written out.
S refers to switch or interlocking. SA specially refers to interlocking plus alarm in one ballon; if alarm is
triggered by switch, then S may be omitted and only A is written.
4.2.2 See Appendix B for various common combination of letter codes.
4.2.3 The first letter expressing measured variable (or initial variable) must be the
starting of letter code (the only exception is the "L" described in the Note (9) in Table
13 of 4.2.1) and one or more subsequent letters expressing function are followed.
4.2.4 The first letter is determined in accordance with measured variable (or initial
variable) but not the instrument structure. For example, differential pressure recorder
used for measuring discharge shall be written as FR but not PdR.
4.2.5 Subsequent letter expressing function is selected in accordance with read or
output function but not the handled variable. For example, the control valve accepting
the signal from liquid level regulator to change flow shall be marked as LV but not FV.
4.3 Writing rule of instrument location number
4.3.1 In ballon, the writing method of instrument location number is: letter code shall
be written in the upside of circle and serial number and suffix shall be written in the
downside of circle, as shown in Figure 9.
Local instrument Board-mounted instrument
Figure 9
4.3.2 Area number and loop number in serial number generally start form 1 and are
compiled in sequence but vacant number is allowed in the middle.
4.3.3 If two or multiple circuits share an instrument, then this instrument shall be
provided with the respective location number belonging to each circuit.
4.3.4 Instrument shall compile the serial number in accordance with measured
variable (or initial variable), namely for the instrument of the same measured variable
(or initial variable) in the same area, its loop number shall be compiled from 1 in
sequence and vacant number is allowed in the middle.
For the instrument of different measured variable (or initial variable), the loop
number is not continuously specified with putting together.
Note: If necessary, for the instrument of different measured variables (or initial variables), the loop number may be
unified and continuously compiled.
4.3.5 Measured variable (or initial variable) with the modifiers "d", "f", "q" shall be put
together with the measured variable (or initial variable) without modifier to compile
serial number and they do not serve as separate measured variable (or initial variable)
to compile serial number separately. For example, temperature difference indicator
TdI-105 shall be compiled the serial number with temperature indicator TI-106 in
accordance with unified sequence.
4.3.6 Only when necessary, modifiers "d", "f" and "q" are added for measuring
instruments. For example, there is no need to add the modifier letter "d" expressing
temperature difference to detecting elements TE-105A and TE-105B which are
connected with TdI.
4.3.7 If there are instruments with more than one same letter codes (i.e., the
measured variable or initial variable have same functions), suffix of capital English
letters shall be added after the loop number to show the difference. For example,
FT-201A and FT-201B can be used to express two flow transmitters in one loop;
FV-311A and FV-311B can be used to express two flow control valves in one loop.
4.3.8 When multiple detecting elements in different zones share one instrument (not
multi-pen or multi-needle instruments), area No. may be omitted for detecting
elements, short dash shall be added after loop number for separation and Arabic
numbers may be added as serial numbering to serve as suffix, e.g., TE-25-1, TE-25-2
and TF-25-3.
4.3.9 Instrument location number for instruments with two or more functions shall be
given according to their complete functions. For example, for flow recorder FR-2
accompanied with pressure recorder PR-4, FR-2/PR-4 shall be written in the detailed
list, UR-7 is also adoptable; double-pen pressure recorder shall be written as PR-7/8.
4.3.10 There is no need to mark instrument accessories in the flow diagram, e.g.,
rotor flowmeter for flushing, air filtration decompressor etc. When one instrument
location number is required, the location No. of its instrument may be adopted, but its
name shall be noted. For example, flange components equipped with orifice plate
FE-7 may be marked as "FE-flange"; rotor flowmeter for flushing - self-operated
control valve group equipped for pressure gauge PI-8 may be marked as "PI -8
flushing".
4.3.11 For simple local indication instruments which are adopted in a large quantity,
e.g., pressure gauge, thermometer etc., if necessary, instrument location number may
not be prepared as prescribed above, letter code of the measured variable is provided
instead, and loop numbers which are arranged in order shall be added after area No.
Area No. may also be omitted, e.g., P-301, P-302…for pressure gauge; T-01,
T-02…for thermometer, etc.
4.3.12 When it is necessary to express high/medium/low (e.g., high alarm, high-high
level interlocking etc.), H (high), L (low), M (medium) or HH (high-high) and LL
(low-low) may be written in top right, bottom right and right side middle part outside
the ballon.
HH or LL indicates that H (high) and HH (high-high) or L (low) and LL (low-low)
exist. However, H or L is omitted and only HH or LL is marked in one ballon.
H, L, M are corresponding to value of measured variable rather than signal value.
For example, for high liquid level alarm provided by reaction liquid level transmitter, H
shall be written at top left outside the ballon mark LA, even though the alarm is
triggered when the signal drops to a certain low value.
H (high) and L (low) may also be used to express the position of valve or other
switching devices: H refers to that the valve is located in or inclines to full opening
position; L refers to the valve is located in or inclines to full close position.
4.4 Additional symbols and codes of relay.
When functions of relay are required to be further expressed, symbols and codes
listed in Table 14 may be filled up in top right outside the ballon.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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