PLC Integration Of PID Temperature Controllers

PID temperature controllers are often a small but vital part of a wider industrial process. For this reason it is important to have oversight of the controller status to establish quickly if the temperature is outside required tolerance. This can prevent downtime, scrap and damage to equipment.

Hardwired Signals

Using hardwired I/O is a simple way to link a temperature controller to a PLC based control system.

Our entry level controller N1030 still has a spare relay output (OUT2) when configured for use with an SSR on OUT1. The OUT1 pulse operates the control process but we can also utilise OUT2 as an auxiliary alarm at no additional cost.

In this example the spare output closes the relay contacts when the control loop is above a set value. This can act as a ‘Ready’ input signal to the PLC and hold off the process if the temperature drops below the alarm setpoint.

Maximising the available Controller Outputs and built in Alarms is a great way to provide status information to a PLC. We recommend looking at the available alarms and spare outputs when specifying a controller for use with a PLC.

A more advanced model such as N1050-PRRR has up to three spare relay outputs which can act as separate PLC inputs to signal the status of the controller.

Developing this idea further, we can introduce the N1200-DIO which has mixed onboard I/O including analogue outputs and digital inputs. This is the controller of choice for system integrators and panel builders with complex requirements.

With the N1200 we can not only monitor the status but also Start/Stop the control loop remotely using input signals. It is an extremely versatile unit which saves time on PLC programming and dedicated hardware.

The N20K48 controller offers all of the features of the N1200 but in a modular format. Input, Output and Communication modules can be added as the process develops. As such this is the best PID Temperature or Process Controller for future proofing. With Bluetooth as standard and a new WiFi module there are many ways to communicate with wider control systems.

Full Communication

Many specifiers of control equipment still select a dedicated Temperature Controller due to the time savings offered. If you are considering developing your own control loop using a PLC it is important to think carefully about the full range of functions required and how long it will take to develop them in logic/code and graphically on a HMI or other display. It is also important to factor in the testing time and hardware cost of any additional modules required.

Despite the PID function blocks offered by some PLC manufacturers it is still very time consuming to replicate even the most basic PID controller when you consider the full range of parameters.

If you are considering full integration with a PLC and the ability to exchange data freely then the best solution is RS485. This allows Modbus protocol messaging between a Master (PLC) and Slave (Temperature Controller). You can read/write Setpoints, recall and run programs and much more. We recommend the following models if you require RS485: 

N1050-PRRR (built in RS485 terminals)

N1200-DIO (built in RS485 terminals)

N20K48 (requires docker and RS485 module)