It’s no secret that well-tuned PID loops contribute to a stable and healthy plant. Once optimally tuned, only critical PID loops that cause too many alarms tend to be tuned again. Underperforming loops are often ignored. But if you frequently analyze all your PID loops you can enhance total efficiency, have less wear and tear, more overall stability, and fewer operator interventions. Read in this blog why it is essential to monitor your PID’s and how to perform monitoring most cost-effectively.
Why is PID monitoring essential?
In a plant, there are often too many PID controllers in the processing unit to monitor individually. The most critical loops will stand out if they are underperforming. But the operator will never analyze the performance of all the loops separately. Retuning all the loops on a regular basis is too time-consuming for both the operator and the engineer. The loops are not all equally crucial, but they all contribute to optimal plant behaviour. Resulting in PID loops who stay under the radar and could be optimized to reach a more stable plant unit. Active monitoring of your PID loops will provide a better performing plant. By making sure the PID controllers are tuned well and in automatic mode, you’ll reach total efficiency:
- Cost-effectiveness
If the PID controllers are tuned well and in automatic mode, the systems can lavish towards the limits of the plant. By reaching this full capacity, the plant can increase its production, lower energy consumption and increase the plant's profitability. - Fewer operator interventions
The better the PID controllers are working in automatic mode, the less the operator has to interfere with the process and have time to optimize in other compartments. - Less wear and tear
If your plant runs properly because of the right automatic PID tuning, there will be less wear and tear of the valves. It will result in less unforeseen repair costs and shutdowns of the DCS.
Set KPI's to monitor your PID loops
To investigate if your PID is stable, you need to set Key Performance Indicator (KPI) for each controller. Such as: percentage in time the PV (Process value) at limit (High-Low), total valve travel in time period, average absolute Error (Error = SP – PV), number of Cross Over changes in manual or maximum PV deviation from SP. To set and monitor these KPI's, you need to have a baseline performance to set the alarm limits indicating underperformance of the controller. Setting the alarm limits right is a tedious job that can take years - yes years and almost a full-time job - to set right. False alarms are not appreciated in the industry and often lead to a "ignore the system" attitude. Combining all the KPI’s together into 1 overall KPI for every PID might also help to find the bad performing controllers.
Monitoring PID loops are expensive and time-consuming
There are many different packages on the market that measure up to 80 KPI's for each controller. They generate a lot of data, but engineers often have no time to look at all these automatically generated reports. Additionally, these packages are expensive. The software price ranges from €50.000 up to €200.000 and more + annual SMS. You need to add the configuration cost on top of that. So, tuning all these KPI's so they do not generate false alarms can be a full-time job. Why not program in your historian some simple KPI's that at least tell you the basic performance of the PID's. For example, is the loop is in automatic (or cascade) mode, or is the OP of the controller saturated (at 0% or 100%)? Setting up a list of basic performance is simple and costs hardly anything. You can generate this list yourself in a simple Excel sheet. When you notice a lot of control loops are staying under the radar you have two options:
- Optimize the loops yourself. You can generate the KPI's and set the alarm limits in the loop until it performs perfectly.
- If this is too time-consuming and you don't want to spend lots of money on inefficient software packages, you can contact a service provider. With the saved money, you can ask the expert to tune all your loops in the plant and come back every year to recheck them.
Monitoring the PID loops in a cost-effective way
So, take a close look at what the software packages can offer you and if this fits in the process of your team. The analysis might be useful, but the reality is that tweaking all these KPI’s until they do not generate falls alarms on the one hand, and do not notice bad acting controllers, on the other hand, might take you years. Keep it simple and don't think the software will take over and all will be good because at the end of the day it all depends on what you and your colleagues can do with it.
Are you looking for a service provider that will analyze your generated list of KPI's and set up a plan to tune all your loops perfectly? Talk to one of our control experts at IPCOS.
Book a meeting with an expert today.
