How to Select a HMI?

A photo about Human-Machine Interface (HMI)

Figure 1: Human-Machine Interface (HMI).
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1. 3 Common Types of HMIs

There are three basic types of HMIs : the pushbutton replacer, the data handler, and the overseer.

1.1 The Pushbutton Replacer

A photo about a worker is replacing costly pushbutton panels with HMI

Figure 2: Replace costly pushbutton panels with HMI.

Before the HMI came into existence, a control might consist of hundreds of pushbuttons and LEDs performing different operations. The pushbutton replacer HMI has streamlined manufacturing processes, centralizing all the functions of each button into one location. The pushbutton replacer takes the place of LEDs, On/Off buttons, switches, or any mechanical device that performs a control function. The elimination of these mechanical devices is possible because the HMI provides a visual representation of all these devices on its LCD screen, while performing all the same functions.

1.2 The Data Handler

Internet of things concepts and tablet with human machine interface

Figure 3: Data handler in industry.

The data handler is perfect for applications requiring constant feedback from the system, or printouts of the production reports. With the data handler, you must ensure the HMI screen is big enough to display information such as graphs, visual representations of data, and production summaries. The data handler includes such functions as recipes, data trending, data logging and alarm handling/logging. The data handler is used for applications that require constant feedback and monitoring. Often these data handlers come equipped with large capacity memories.

1.3 The Overseer

Anytime an application involves SCADA or MES, an overseer HMI is extremely beneficial. The overseer HMI will most likely require Windows to operate, and have several Ethernet ports. The overseer works with SCADA and MES. These are centralized systems that monitor and control entire sites or complexes of large systems spread out over large areas. A HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information.

A diagram about HMI is usually linked to the SCADA system

Figure 4: A HMI is usually linked to the SCADA system.

2. How to Select a HMI

An HMI is a substantial purchase, so it is important to know exactly what is required of it. HMIs typically perform one of three primary roles: a pushbutton replacer, a data handler, or an overseer. The pushbutton replacer HMI takes the place of LEDs, On/Off buttons, switches, or any mechanical device that performs a control function. The Data Handler is used for applications that require constant feedback and monitoring. Often, these data handlers come equipped with large capacity memories. The overseer works with SCADA and MES, centralized systems that monitor and control entire sites or complexes of large systems spread out over large areas. An overseer HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information.

First consider the other components that are necessary to make a manufacturing control system operate. The production line consists of all the machinery that performs the work required in the production of the product. Next, consider the various input/output sensors that monitor temperature, speed, pressure, weight and feed rate. Third, decide on the programmable logic controller (PLC) that will receive the data from the input/output sensors, and converts the data into logical combinations.

Select an HMI based on the needs of the system. HMIs are initially separated by their display size; typically spanning from 4.3" up to 15" diagonal. Within these sizes, HMIs are separated by their characteristics, namely their communication capabilities. HMIs with multiple COM and/or Ethernet ports will usually be more costly, but will allow for an overseer type application to be well connected to multiple PLCs. Make sure that the communication protocol your PLC uses can connect to the HMI by first verifying the protocol of the PLC and ensuring it exists on the HMI Communications and Connections Guide.

If you have a system that has many very simple and repeatable processes, you may not need an HMI with a large memory capacity. In this instance, you can choose an HMI based on size and choose one with the appropriate price point.