Phase 5: Selection of HMI
In this article we discuss the selection of the HMI / SCADA (index of design phases).
5-Selection of HMI or SCADA
In medium or large systems, normally the operator interface is defined in the technical specification. If it is a PLC system we will talk about a SCADA, if it is a DCS we will talk about the operator stations.
In small systems with a single PLC there are other options to consider such as operator terminals or low cost SCADA.
Large end users typically specify the brands of the entire control system and this includes the HMI. In any case let’s see some questions that we should ask ourselves when selecting the HMI /SCADA depending on whether we are the end user or the system integrator:
i) Do I want it to be compatible with my existing hardware?
ii) What degree of scalability should it have?
iii) What level of technical assistance do I need?
iv) Is it easy to update to new versions and at what cost?
v) Can I carry out the maintenance myself?
vi) What is the licensing policy and its cost?
vii) Does it have proven references in systems with many variables?
viii) Does it have references and libraries in similar applications?
ix) What communication options does it have and how secure they are?
x) What other available products are compatible with this SCADA (MES, Historian, Data Analytics, Asset Management, etc.)?
xi) Does the company behind the product give me confidence?
xii) What is the experience of the system integrator?
i) Am I already trained in this SCADA?
ii) Have I already used it in a similar application?
iii) Is there technical assistance in case of need?
iv) Does it have references in systems of a similar size?
v) Does it have references, libraries and complete functions for this type of application?
vi) Are communication drivers that I need available?
vii) Do I have confidence in the company behind the product?
Nowadays, in the environment of the digital transformation that we are living, there are other aspects that we should take into account when choosing the HMI, like the remote access to the system from web browsers, mobile phones and tablets, or what is related to cybersecurity (encryption, authentication, firewalls, etc.)
We also want to reflect about the differences between the PLC and DCS. Many discussions about this topic forget that the systems based on PLC + SCADA have developed a lot in recent years and have nothing to do with those available 15 or 20 years ago. In any case, especially in large applications, there are still significant differences that have to do mainly with the number of databases (unique in the case of DCS) and the advanced control features that we can find in some DCS manufacturers which have specialized in specific applications (refining processes, generation plants, etc.)
They are the signals that are exchanged between two controllers or between a PLC and the DCS using a communications bus. In this case you must define the physical support (RS232, RS485, Ethernet, etc.) and the protocol used (Modbus RTU, etc.).
For example, in large facilities it is common to have PLCs in the package units that communicate with the DCS.