PID Drawings
A PID (Piping and Instrumentation Diagram) is basically what the name implies. It is a diagram of a process that contains the Instrumentation components as well as shows how they are all connected in the field.
Knowing how to read a PID is important as an Instrumentation Technician. It gives you the key pieces of a process as well as gives you an idea how the process functions. This makes it invaluable for troubleshooting. Before you start pulling something apart always consult the PID and Loop Diagram.
As important as PIDs are, it may be quite difficult to get a hold of the correct PIDs. It is common for a plant to misplace or not have their PIDs up to date.
I’d like to share a picture of a very basic PID with some explanation. This PID covers the Glycol System for a boiler. The glycol is heated by the steam in the heat exchanger(HE-1). The Glycol runs through the Air Separator(AS-1) and is then pumped up to the roof fans where it is cooled before returning to the heat exchanger.
PID Naming Convention
Notice how some of the symbols on the diagram have a certain name. For example PI or FS. A PID has a naming convention that describes the process property as well as component type. Look to the following chart for an example.
First Letter | Second or Third Letter | |
A | Analyzer | Alarm |
B | Burner | |
C | Conductivity | Controller |
D | Density | |
E | Voltage | Element |
F | Flow | |
G | Glass | |
H | Hand | |
I | Current | Indicator |
J | Power | |
K | Time | |
L | Level | Light |
M | Moisture | |
N | ||
O | Orifice | |
P | Pressure | |
Q | Quantity | Totalyzer |
R | Radiation | Recorder |
S | Speed | Switch |
T | Temperature | Transmitter |
U | Multivariable | |
V | Vibration | Valve |
W | Weight | |
X | ||
Y | Event, state, presence | |
Z | Position | Actuator |
Learning this chart was the first thing I did as an Instrumentation Apprentice and it has proved useful on multiple occasions. Let’s say you were assigned to fix PI-1 on the Glycol system. Without knowledge about what PI means, you may be looking for a while. Knowing that PI means pressure indicator you know you should be looking for a device that indicates pressure. This is typically a pressure gauge.
PID names aren’t stuck having 2 letters either. It is common to have a suffix of IT such as PIT(Pressure Indicating Transmitter) or FIT(Flow Indicating Transmitter). I will go into greater detail of what that all means in our next article.
