For my final Simple Saturday post of the year/decade I will cover terms and acronyms used as part of shutdown systems.
ESD: Emergency ShutDown. This is the generic name given to a system that trips the plant if it detects a problem. This generic name could refer to simple …
Since starting work after leaving university, I have found several terms thrown around when talking about the control system. In every factory I have worked in, they have had a DCS, though some parts of it were controlled by PLCs. In some documents or training courses, I have seen references …
Continuing after last week's discussion about process noise, I will now cover another tool used to help mitigate noise.
Deadbands are useful when the the result is a digital signal, it is either on or off. Most control loops are analogue and have a range of outputs, usually a control …
Previously I have talked about noise in the measurements that are used to control the process. These variations can cause the system to react unnecessarily and introduce disturbances to the process.
While we should always try to avoid noise by selecting suitable instruments and installing …
What is noise? Depends on what subject you are talking about. If you are talking about what your ears sense, then it is a bunch of pressure waves that move through the air. But in the case of this post, I am actually talking about noise in a process control …
When a control valve opens, the flow through it increases. But the increase in flow is not necessarily linear, the rate of change in flow may be different depending on how far open the valve already is.
If the flow through a valve was linear, every time the valve opens …
When a control loop is placed in manual, the output is fixed. It doesn't change any more, it stays where it was or where the operator sets it. As a result, the process can change significantly, the measurement or PV (Process Value) can go much higher or lower than where …
A fellow chemical engineer told me that there are only two things about electricity that a chemical engineer needs to know:
Anything else is a problem for an electrical engineer.
While I do enjoy learning about other disciplines, I generally agree with …
Alarms are the control system's was of shouting at the operator. If saying "STOP WHAT YOU ARE DOING AND LOOK AT THIS". The problem is that it takes time for the operator to stop what they were doing, look at the alarm. Then look at what else is going on …
This post explains different types of alarm that can be used on a control system.
These are the simplest type of alarm. The control system measures something such as pressure, temperature, level or flow, and compares it with the alarm value. If the measured number is …
Alarms are a common feature of all control systems. They are a way of letting the control system shout "HEY, STOP WHAT YOU ARE DOING AND LOOK AT THIS" to the operator.
They are set off when a reading such as s temperature or a level, goes beyond the range …
I do not think that we covered override control loops while at university, the first time I came across them was in the sugar factory. Yet they are used a lot and are incredibly useful. I don't understand why they aren't covered in introductory control classes.
Override control can come …
Most control loops try to keep whatever is measured at a value set by the operator (SetPoint, SP). Sometimes the operator lets something else decide the setpoint. This is called cascade.
In most cases this means two control loops work together. The output of the first decides the setpoint of …
In last week's edition of Simple Saturdays, I talked about control loops. This week I will talk about the PID loop. Unlike many explanations of the PID loop, I will keep it simple. I will avoid showing the equation that a controller uses. The truth is that as a control …
The way we manage to get our factories to make the things we want them to is by getting liquids to flow various pipes at the right speeds, by making sure they are at the correct temperature. We need to ensure tanks don’t overflow and the pressure inside is …
In the first of my simple Saturday posts, I will cover the term partial pressure. This term is critical to much of chemical engineering and I was very familiar with it during my time at university. But once I graduated and worked in a sugar factory, I didn't use it …
I dislike the amount of jargon we tend to use in our daily work lives. We use acronyms like CCR (central control room) rather than just saying "control room". We refer to equipment tags like P101 rather than simply describing the equipment like "feed pump". It is not as if …
