Symbols for instrumentation layouts

For Chemical Engineers involved in either design or production activity, it is necessary to be able to distinguish various types of field and indoor instrumentation and control systems used for particular industrial applications. In order to make layouts uniform and to visualise the process control system a set of symbols was introduced. The following symbols were taken from: Australian Standard - AS 1101.6-1989, Graphical Symbols for general engineering. Part 6: Process measurement control functions and instrumentation, Standards Australia, 1989, 52 pp.

Figure :. presents symbols for industrial instrumentation.

Diameter of a circle for the symbol is equal to 10 mm. Meanings of identification letters for these symbols are presented in Table .

To better understand how these symbols are placed in process control and instrumentation flowcharts I decided to give several examples for measuring and control of process variables in a variety of industrial processes in the successive posts.

Table : Meanings of identification letters.

First Letter			Succeeding Letters
Measured or initiating variable		Modifier	Readout or passive function	Output function	Modifier
A	Analysis		Alarm
B	Burner flame		User’s choice	User’s choice	User’s choice
C	Conductivity (electrical)			Control
D	Density (mass), specific gravity	Differential
E	Voltage (e.m.f.)		Primary element
F	Flow rate	Ratio (fraction)
G	Gaging (dimensional)		Glass
H	Hand (manually initiated)				High
I	Current (electrical)		Indicate
J	Power	Scan
K	Time or time schedule			Control station
L	Level		Light		low
M	Moisture or humidity				Middle or intermediate
N	User’s choice		User’s choice	User’s choice	User’s choice
O	User’s choice		Orifice (restriction
P	Pressure or vacuum		Point (test connection)
Q	Quantity or event	Integrate or totalise
R	Radioactivity		Record or print
S	Speed or frequency	Safety		Switch
T	Temperature			Transmit
U	Multivariable		Multifunction	Multifunction	Multifunction
V	Viscosity			Valve, damper
W	Weight or force
X	Unclassified		Unclassified	Unclassified	Unclassified
Y	User’s choice			Relay or compute
Z	Position			Drive, actuate

                                                        Article Source:: Dr. Alexander Badalyan, University of South Australia