Multi-sensor, multi-channel, multi-parameter analyzers can greatly reduce the cost per point of any measurand including pH, residual chlorine, ORP, ozone, chlorine dioxide, dissolved oxygen and turbidity measurements without sacrificing the quality of those measurements.

Multi-Parameter Analyzers - CRONOS<sup>®</sup> and CRIUS<sup>®</sup>

Multi-Parameter Analyzers – CRONOS® and CRIUS®

The CRONOS® and CRIUS® controllers both allow the connection of multiple sensors. For example, a CRIUS® may be made up of multi-sensors of the same variety such as up to four chlorine sensors, or could be made up of a mix (multi-channel analyzer), such as a pH sensor, a chlorine sensor, and a turbidity sensor. Whatever your requirement for a multi-channel analyzer the CRONOS® and CRIUS® ranges will provide what you need.

Highest Quality – Lowest Cost Multi-Parameter Analyzer

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® can also come in a multitude of languages making it suitable for use in any market.

Customers requiring additional functionality such as downloadable datalogging or remote access via the internet should consider the CRIUS® controller.

Highest Quality – Low Cost Multi-Parameter Analyzer

The CRIUS® offers more sensor connections, more functionality and more flexibility with a color screen and optional built in 3G modem. The CRIUS® is an attractively priced, top of the range instrument controller. Optional communications packages allow Profibus, Modbus ASCII, Modbus RTU, Modbus TCP and others.

The CRIUS® is equipped with the capability to connect up to four sensors of any type with appropriate analogue outputs and relays. Four sensors not enough? Simply connect up to 4 CRIUS® together all using the same display and communications. Equipped with datalogging as standard and multiple PID loops as options, the CRIUS® is very able to control complex water treatment processes at a fraction of the cost of other controllers.

The CRIUS® can also come in a multitude of languages making it suitable for use in any market.

Customers requiring a no-frills controller should consider the CRONOS® controller.

Multi-Channel Analyzer Option - Remote Access

Multi-Channel Analyzer Option – Remote Access

  • Low cost per point
  • Process control options
  • Remote access options
  • Stable, reliable, accurate sensors

Multi-channel online analyzers from Process Instruments all maintain their level of functionality and include:

  • 4-20mA outputs
  • Assignable relay outputs
  • Intuitive menus
  • Text alarms to your mobile
  • High resolution displays
  • Graphing and datalogging
  • 9 buttons for easy navigation
  • Enclosure; wall, panel, pipe or pole mounting. IP65/NEMA 4x.

The CRONOS® and CRIUS® multi-sensor systems are equipped with process control options, relay outputs, serial communications, (TCP, Ethernet, Modbus and Profibus). In fact the multi-sensor systems have all the options you could want in an online analyzer whilst maintaining a low cost and great value for money.

Multi-Sensor System - AquaSense

Multi-Sensor System – AquaSense

Typical Configurations

  • Multiple channels of pH, residual chlorine, turbidity, chlorine dioxide
  • pH and chlorine
  • ORP and chlorine
  • pH and chlorine and turbidity

Summary of Applications

  • Water Treatment
  • Drinking Water
  • Waste Water
  • Pool and Spa Control
  • Industrial Water
  • Food and Drink
  • Paper and Pulp

Multi-Sensor System - CoagSense

Multi-Sensor System – CoagSense

The CRONOS® is often used in applications where the remote access capability of the CRIUS® is not required. The CRONOS® is a universal controller capable of outputting a PID signal via an analogue (4-20mA) or a pulse width modulated relay (to control for example, an on/off pump). With the latest in communication options, the CRONOS® is capable of running Profibus, Modbus or TCP/IP via Ethernet.

The CRIUS® is preferred in the swimming pools market, where the superior control and sensor capability provides for better quality bathing water. Again the remote access is proving essential to our customers along with the Variable Speed Drive (VSD) control which is massively reducing electricity usage and CO2 emissions (and reduces electricity bills!).

In the municipal drinking water market, the superior control capability of the CRIUS® is making it the controller of choice for areas like coagulation control with the superior sensors in use, particularly for chlorine control and dissolved oxygen control.

Both multi-channel analyzers have a number of options available.

CRONOS® options include:

Multi-Channel Analyzer Option - Graphing and Datalogging

Multi-Channel Analyzer Option – Graphing and Datalogging

  • Modbus RS485/LAN
  • Profibus DPV 1
  • PID/flow proportional controls
  • Remote sensors
  • Color display
  • Downloadable data logs

CRIUS® options include all CRONOS® options plus:

  • Remote access via LAN
  • Remote access via 3G/4G
  • Expandable to 16 sensors

Document Type Size
CRONOS® Brochure 610kB
CRIUS® Brochure 605kB
CRIUS® Remote Communications Brochure 573kB
CRONOS® and CRIUS® Control Options Technical Note 534kB
How To Specify a Pi Analyzer Technical Note 626kB
Remote Access GPRS Technical Note 481kB
PID Control Technical Note 1.3mB

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.

If you have used a Pi controller you will know that they give you unrivalled control options but did you know that Pi’s new controllers also offer individual security for up to 20 named individuals?

Pi’s controllers have always given flexibility but did you know that Pi’s new controllers can accommodate up to 16 sensors of any description?

CRONOS<sup>®</sup> Controller

This Focus On describes the 10 most popular innovations to be found in Pi’s new CRONOS® and CRIUS®.

No. 1 – Human readable service log

Both the CRONOS® and CRIUS® analyzer/controller has a downloadable human readable service log – giving an entire history of the instrument including current settings, calibrations etc. Provides a great snapshot of how an engineer left an instrument.

No. 2 – Cloning facility

Ever had to set up many instruments with the same settings? Simply set up one and copy it to others!

Connections ExampleNo. 3 – On screen wiring diagrams

Lost the manual or can’t be bothered to find it? Pi’s analyzers have the answer!

No. 4 – Want a bit more info on what’s going on with a sensor?

Pi’s new sensor maintenance pages are just for you then! Detailed information about all aspects of the signal coming off the sensor clearly available.

DatalogNo. 5 – Instrument datalogs not quite giving you what you need?

Pi’s new look datalogs in CRONOS® and CRIUS® (downloadable) let you datalog almost everything, put graphs on the display, datalog the same parameters at more than one interval and a whole lot more. Never has instrument datalogging been so easy and complete.

No. 6 – New enclosure

The new enclosure brings a new level of flexibility being wall mountable, pole and handrail mountable and even flush mountable. Not only that, but it gives you loads of room to work in and there are even spare live, neutral and earth terminals to make wiring relays easier!

No. 7 – Not enough I/O?

Don’t worry, simply daisy chain 4 CRIUS® together and you can use the same display, comms options etc. and increase your I/O fourfold to give up to 16 sensors.

No. 8 – Bored of reading about stuff in manuals that you don’t have?

Pi’s new manuals are bespoke to each instrument. The manual is ‘built’ to match each individual instrument so the manual only has what you have!

CRIUS<sup>®</sup> Controller

No. 9 – Has the operator been messing with settings they shouldn’t?

No more! With 20 individual user settable logons, you can give people access to what they need and no more.

No. 10 – Control algorithms

Pi has developed a reputation for developing great control algorithms and this has continued with the new CRONOS® and CRIUS® with the introduction of feed forward control algorithms and a master controller which selects the correct control philosophy to use (for use with complex systems such as coagulation control).

You probably know that water monitoring controllers can be connected to site SCADA systems, but…

… did you know that with Pi Remote Access you can change settings on the controller from your home or office without setting a foot out the door?
… did you know that you can still access the controller, even if it’s in an area with no network signal?

What is Remote Access?

Pi Remote Access is a cloud-based server designed to save you time and money. Ever wished there was a more convenient way to access your water monitoring controller? Tired of wasting time driving to sites miles away just to change settings? Welcome to our Remote Access service…

Remote Access GraphsPi’s Remote Access server draws information from the controller on site and displays current device values and historical graphs. The server is designed to be as user friendly as possible. The graphs can be adapted and manipulated, giving you the freedom to display information however you want.

We have designed the Remote Access to have a two way interface. This means that not only can you view nearly every setting on the server that can be seen on the analyzer itself, but you can also alter these settings too. Logging on to our Remote Access server really is like being stood in front of the controller itself!

Remote Access DevicesThe best thing about our Remote Access service is it’s free! There is just the initial cost of equipment required to access the server, but no ongoing service cost after that.

Here at Pi, we know from experience that one size does not fit all. Each site has its own connectivity issues and access restrictions. That is why we have designed our Remote Access to be accessible through a variety of different options, which are outlined below. If you are unsure about anything, don’t hesitate to get in touch, we will be happy to help.

If Your Facility has a LAN (Local Area Network)

In this case, the controller can be connected to the LAN on site with an ethernet cable. We provide you with your own Remote Access account which enables you to use our server. Depending on the LAN settings, a VPN (Virtual Private Network) and/or dynamic DNS (Domain Name Server) may be necessary for the controller to connect to our Remote Access server.

Is your LAN access restricted, or ever not connected to the internet?! No problem! We have other options for you…

LAN Access Restricted or no LAN at all

If LAN access is restricted or there is no LAN on site, we can provide a GPRS modem with a SIM card instead. This will provide a fixed IP address, enabling you to use the Remote Access server. This is available in nearly every country around the world. The SIM card works very much like the one in your mobile phone, it requires sufficient network signal for the Remote Access to work effectively. There are charges for data usage paid to your network provider, but these charges tend to be very low due to the small size of the data required to use the Remote Access.

No network signal?! No problem! We have a Remote Access solution for that too…

Remote Access Hardware AdapterLAN Access Restricted and no Network Signal

If LAN access is restricted and there is no GPRS network signal either, an external server box is the solution. This is a common option used in hospitals, as access to their network servers is often restricted. The external server box is attached to the controller via an ethernet cable and generates a WiFi network. Accessing this WiFi network through your computer will enable you to connect to our Remote Access server.

Even with restricted LAN access, if the site has a designated VPN, you will be able to use this to access the analyzer and connect to the server from your home or office, without needing to go to site.

Did you know…

… that PID can save you money by offering better process control?
… that PID can help you maintain a setpoint, even with a variable process?
… that the days of over complex and confusing PID are over?
… that Pi can tailor a PID system to your exact requirements? You may never have to touch those settings again!

In this Focus On, Pi would like to introduce you to PID if you haven’t come across it, and discuss some of the useful advanced features of modern PID systems, like on Pi’s CRONOS® and CRIUS® models for those more familiar with PID.

Introduction to PID

What is PID?

PID is a mathematical tool created by engineers and is used in controllers. It is a feature often found in industrial controllers and is available in Pi’s controllers, as an inexpensive upgrade.

What is PID for?

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.

When a person enters a swimming pool, they create a chlorine demand. They do this by introducing sweat, bacteria, organic molecules and other substances into the pool water. Chlorine reacts with these substances, which results in chlorine being used up and the chlorine level dropping. The chlorine level in this example, is often called the process variable or PV in the context of PID.


In order to maintain a concentration or level of chlorine, more chlorine needs to be dosed. If you dosed the same amount of chlorine per bather, the level would not be stable as all bathers create a different chlorine demand (e.g. swimming for fitness produces more sweat than swimming recreationally). Dosing manually brings in the issue of human error, and how operators approximate or calculate the amount of chlorine to dose based on current levels. Another issue with manual dosing is that it is not a continuous process, meaning it is unlikely a stable level will ever be reached.

What does PID do?

PID takes the measured level of chlorine or the PV and compares it to the desired level or set-point. This comparison gives the error which PID interprets and then calculates an output. The output is an electrical signal which controls the dosing of the appropriate chemical. The output can control heaters, dosing pumps and many other mechanisms that can be used to change the PV.

How is it used?

PID is made up of three parts, proportional, integral and derivative. Understanding what each part does helps operators choose the level of control best suited to them.

Proportional – Is the most commonly used for portion PID and suits most applications. When using proportional control, the further away the measured value is from the setpoint, the larger the output will be from the controller. This is an appropriate level of control for most processes, and users can gain a lot of control from a purely proportional system.

In some systems where the PV is lost to the process, e.g. chlorine from a pool, heat from a boiler etc., the proportional control never quite catches up with the setpoint. Users can see that although the process approaches the setpoint it rarely, if ever, gets to it. This is known as ‘droop’. The user can compensate for droop if the removal of the PV is fairly constant, simply by raising the setpoint, e.g. evaporation of chlorine from an empty pool. If droop changes often, (e.g. bather load or chlorine demand) then to eradicate the ‘droop’ then the integral part of PID can be applied to the signal to correct it.

PID vs Threshold

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.

Derivative – Derivative gain is rarely used and is generally set up only by expert engineers. Derivative gain uses the rate of change in the PV to try and predict future errors. This type of control is particularly susceptible to overcompensating, especially if there is even a small amount of signal noise (usually seen as spikes in the PV). Derivative gain is generally a tweak used by engineers to improve an already tight control, and is almost never used as an essential part of control.

PID Control

What are the benefits of PID?

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 analyzer 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.

Advanced Features and Safeguards

Whilst maintaining a setpoint with a PID loop is a huge advance over using threshold relays to maintain an upper and lower limit, it is sensible to control the loop with extra safeguards, such as:

  • Maximum and minimum pump outputs. This is mainly used to prevent the controller from employing too aggressive a control, which can lead to overdosing. A minimum output can also be used in a system where the measured parameter is lost over time, to prevent the controller ever turning the dosing off.
  • Ramp rate is a proportional control that allows users to choose how quickly or slowly the controller doses, in order to reach the setpoint. It is especially useful on startup, and can prevent the controller dosing too quickly.
  • Wind up protection is an integral control, which limits the duration aspect of the control. This puts a limit on how much previous error can accumulate. Without wind up protection, there could be a very large integral value, if the process ever reaches zero or on startup.

These are all standard features in all Pi PID controllers.


In summary, PID is a very useful tool when used correctly, and can result in significant chemical savings, not to mention reduced pump wear and tear and lower electricity costs.

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Email: [email protected]

Tel: +44 (0)7908 765113

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happy to help."

Karen Thirlwell

Head Office Contact