Part of a range of controllers, the CRONOS® is the little brother of the CRIUS®4.0. The CRONOS® is a high quality, low cost transmitter designed to give water treatment engineers everything that they need from a transmitter and nothing that they don’t. With no frills, costs can be kept to a minimum whilst optional communications packages allow Profibus, Modbus ASCII, Modbus RTU, Modbus TCP, 4-20mA analogue outputs, and relays for alarms and control.
The CRONOS® has the capability to control up to two sensors of any type with appropriate analogue outputs and relays. Equipped with optional PID control, the CRONOS® is very able to control complex water treatment processes at a fraction of the cost of other controllers.
The CRONOS® is often used in applications where the remote access capability of the CRIUS®4.0 is not required. This doesn’t mean that a CRONOS® doesn’t have the capability of control!
With full PID control, the CRONOS® is often used in application areas such as:Up to 2 analogue outputs and 8 relay outputs.
Focus Ons are a series of short articles distributed by email providing technical information regarding instrumentation, process measurement in potable, waste, process and pool waters. If you would like to join the mailing list, please contact us.
Description: Some pumps can now be controlled using digital communications such as Modbus or Profibus. These are designed to be used directly from PLCs and they give operators distinct advantages over more traditional methods. A digital signal has longer range, has a signal cable for 2-way communication, and is able to transmit far more detailed information than a simple on/off alarm signal.
Control with the DDA e-box can also be extremely precise, with the pump more able to correct the pump output to very closely match the scale used by the analyser. A pump being controlled by a 4-20mA scale, asking for 60% of the pump’s output, was more than a litre off the real value of 60% of the pump’s scale. This means that on a 0-30l/h pump, a pump controlled by a 4-20mA signal calling for 60% of the pump’s output would actually be pumping 19l/h, whereas a Modbus controlled pump would be pumping 18l/h. This difference is small but measurable, and over a pump’s lifetime would add up to a remarkable discrepancy in chemical. It’s likely that with longer cable lengths, on a real site, this discrepancy would increase.
Process Instruments supply CRIUS®4.0 and CRONOS® controllers with sensors for many single parameter systems like chlorine and pH but did you know that…
…Pi’s CRIUS®4.0 and CRONOS® controllers both allow the connection of multiple sensors?
…Pi’s multi-parameter systems can save you space onsite, are easy to use and have a number of communications options available?
…Pi’s CoagSense coagulation controller is a multi-parameter system that is now a key part of Pi’s product range?
An example of one of Pi’s most in demand multi-parameter analyser combines a CRIUS®4.0 with a TurbSense® turbidity meter, a pHSense pH meter, a ConductiSense conductivity meter and a UV254Sense UVA analyser with a temperature sensor on raw water systems. These have proven to be very popular in applications where companies and local authorities are looking to save on installation time, space and upfront costs.
The CRIUS®4.0 is equipped with the capability to connect up to four sensors of any type with appropriate analogue outputs and relays. If four isn’t enough, don’t worry. The CRIUS®4.0 can connect up to sixteen sensors by adding expansion boxes where needed, all using the same display and communications.
Equipped with data-logging as standard and multiple PID loops as options, the CRIUS®4.0 is a cost effective alternative to multiple single sensor analysers, reducing cost while maintaining the highest quality.
Optional communications packages allow Profibus, Modbus ASCII, Modbus RTU, Modbus TCP, 4-20mA analogue outputs, and relays for alarms and control.
Customers requiring a no-frills controller should consider the CRONOS® controller.
The CRONOS® has the capability to control up to two sensors of any type with appropriate analogue outputs and relays. Equipped with optional PID control, the CRONOS® is very able to control complex water treatment processes at a fraction of the cost of other controllers.
Finding space is becoming a real problem for installation engineers across many sites at the moment. As water supply companies are looking for more and more information and regulation increases, this has resulted in more and more instrumentation being installed. Most water treatment plants have limited wall space and finding room for new instruments is a real challenge. Both of Pi’s instrument controllers as multi-parameter analysers are solutions to this problem.
With simple ‘plug & play’ inputs and outputs, intuitive display and button control, and with an individual manual configured to be the same as your analyser, the CRIUS®4.0 and CRONOS® make setup and ongoing use, simple and easy.
Modbus and Profibus communications are available which further cut down on wiring costs and PLC, SCADA input costs.
Pi’s remote access allows the user to connect their CRIUS®4.0 through their local network (LAN) or a 3G/4G mobile network connection. This connection allows the user to have full control of their analyser from any computer, tablet or mobile phone.
The CoagSense coagulation controller combines a StreamerSense streaming current sensor, a UV254Sense UV analyser and a pHSense pH sensor to automatically control pH adjustment of the raw water and also the coagulant dosing in water treatment plants. A TurbSense® turbidity meter can also be added if required.
The controller has revolutionised the industry where one controller can now monitor and automatically control your dosing pumps by sending a flow proportional signal direct to the dosing pumps, or to the plant’s SCADA. Previously, all of this had to be done by a PLC or a SCADA system which involved getting a specialist programmer on site and increased costs. Now there is a controller that does all of this in an affordable manner.
Process Instruments (Pi) are increasingly seeing water engineers and technicians relying on their PLC’s PID auto-tune feature. Many are becoming frustrated that the auto-tuners are unreliable when it comes to water processes. Sometimes the auto-tuned PID settings work, but then something changes in the process and the PID control no longer functions correctly.
In this Focus On, Pi aims to outline how PID auto-tuners work and why they are often unsuitable for complex water treatment processes. We also give a brief introduction to some of the principles of tuning a PID manually.
Did you know that…
…auto-tuners are not effective at tuning processes with long loop times?
…the CRONOS® and CRIUS®4.0 have many built-in PID safety features to make control easier and safer?
…PID loops can often be tuned remotely, meaning huge savings on site visits and travel time?
A Proportional – Integral – Derivative (PID) controller is a control loop feedback mechanism widely used in industrial control systems. PID controllers allow a system to continuously and automatically modulate a control mechanism (e.g. a dosing pump, a valve, motor speed), to attempt to achieve a desired setpoint.
There are a myriad of ways that a PID controller can be ‘tuned’. In a very basic PID controller, the operator can choose how much of their control should be based on P, I and D. In reality, D is almost never required in water processes due to the nature of the control loop.
This is generally what ‘auto-tuners’ undertake. They make small changes to the ratio between P, I and D control, track the response, decide if the change is good or bad, and then change again.
So what the auto-tuner is doing is changing, measuring, and changing again; which can work perfectly on processes with a very short loop time (time between a change and a response from the system), the auto-tune making many changes in a short amount of time. The changes cumulate into a ‘tuned’ PID system.
On the right is an example system of a PID auto-tune.
In the diagram, we can see that for the system to work, the box in red is a crucial part of the process. If the change brought on by the PID auto-tuner isn’t visible quickly enough, it may affect the way the auto-tuner categorises the change (good or bad), or won’t give the auto-tune the opportunity to make enough iterative changes to bring a complex water system under control.
There is good news for water technicians and engineers and that is that Pi are here to help. All our salespeople are application specialists and are all capable of helping you manually tune a PID controller for your processes. Our CRONOS® and CRIUS®4.0 controllers are both capable of delivering excellent control in many processes, and have many built-in PID features to help make your process more controlled, robust and safe.
In many ways, the auto-tuners mimic plant engineers making adjustments and tuning their PID settings. They simply lack 2 key components;
With this in mind, here is how our engineers approach PID tuning on our instruments;
Once you have the basic P and I ratio sorted, or if you are unable to get the P and I into control, it is worth considering these additional settings which will help make your control scheme more robust and safer.
Even armed with all this knowledge, PID tuning can be a bit of a dark art. What works on one site may not work on another and even experienced engineers sometimes call us for help.
One of the ways we can help is using our remote access system InSite. Our Remote Access portal (Control InSite) allows people with the appropriate security clearance to make changes to settings and observe measurements from their desk.
Sales Manager, Dr. Rob Paramore, recently described his experience of changing a customer’s PID settings (at their request), whilst talking them through what he was doing on the phone:
Pi’s VSD control sets the recirculation pump motor automatically, while the pool is being used, based on biocide demand. Biocide demand is directly linked to the number of people using the pool or spa, therefore Pi’s controllers can reduce pump speeds and electricity costs during periods of fewer bathers.
For a commercial swimming pool (210m3) the monthly savings on electricity using VSD control were calculated.
From these results it can be seen that Pi’s VSD control saved £213 a month at this single commercial swimming pool. This is a significant reduction not only in cost but also the CO2 footprint of the site. The larger the pool and spa, the bigger the pump that is required to recirculate, therefore the more money that can be saved on electricity. Using the VSD control; Pi’s controllers could pay for themselves in 6 months or less.
The best way to explain what PID does, is to take an example. Most people have been to a swimming pool at some point in their lives, so this is the example we shall use. PID is also applicable in a huge variety of other processes. If you are not sure, you can always contact us to discuss your application.
Integral – The output from the integral term is determined by both the magnitude and the duration of the error. A small error over a long period of time will trigger a larger response than from a purely proportional system. This helps the elimination of the ‘droop’ seen in processes with continuous loss, and also serves to help reach the setpoint quicker.
When properly set up, PID can lead to far tighter process control, which in turn can save you time and money. As an example, pool managers want to keep chlorine levels low, to improve the bathing experience and also save on chemicals. AquaSense is a chlorine analyser system that responds quickly and appropriately to a change in bather load (also known as chlorine demand). This means pool operators can save money whilst maintaining the safety of the pool. PID can also help reduce the risk of overshooting the desired setpoint, reducing the risk of dangerous overdosing of the chemicals.
| Document | Type | Size |
|---|---|---|
| CRONOS® | Brochure | 656kB |
| How To Specify a Pi Analyser | Technical Note | 815kB |
| CRONOS® and CRIUS®4.0 Control Options | Technical Note | 608kB |
| PID Control | Technical Note | 710kB |
| VSD Control to Reduce Swimming Pool Electricity Bills | Technical Note | 665kB |
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