Microcontrollers and programmable logic controllers (PLCs) are used to monitor and control many types of sensors and devices on a wide range of industrial equipment. A common thread among these applications is that the controller still needs a way to physically and electrically connect to input / output (I / O) signals. This usually takes the form of a screw terminal, pluggable design terminal (PID), or perhaps a connector, which is the point where the integrated I / O electronics pass to a wire going to a field device.
This interface for transmitting and distributing signals can be achieved in several ways, but it usually takes up a lot of space compared to the controller itself, and the interface is also a point of failure. As systems become more complex with more automation and more I / O points, the need for compact and reliable interface methods becomes evident. This article discusses the features of the interface module that designers should look for and the benefits of choosing a universal system.
Types of signals
Most industrial systems rely on a small variety of signal types. Discrete (on / off) signals are generally 24 VDC (although in some cases they can reach 120 VAC or 5 VDC), and they almost always have a fairly low current. Analog signals generally operate in the 4-20mA or 0-10VDC range. There are also specialized signaling levels for thermocouple and RTD temperature measurement, millivolt strain gauges and more. In summary, a large portion of industrial I / O signaling needs are for low voltage and current.
However, there are still cases where higher voltage and current switching may be required, or electrical isolation is required, such as when operating motor starters, frequency converters, large solenoids, and electric heaters. In these cases, relays can be used as an interface point as they are designed to use a small switching signal to operate a different and often higher power output signal, while also providing electrical separation and isolation. . Additional complications arise because the relay signals can be NPN or PNP, with several different types of contact form factors. Installing many relays in a control panel is expensive in terms of labor and space efficiency, and they can be difficult to troubleshoot and maintain.
A final point is that most digital controllers are designed to be compact, and to achieve this all I / O signal points are condensed into a connector format. Some typical connector types for on-board controllers or I / O modules include:
- IDC (14 pin, 20 pin, 26 pin, 30 pin, 34 pin, 40 pin)
- Sub-D (37 pin, 44 pin)
- MDR (50 pin, 68 pin, 100 pin)
- Terminal blocks
Designers need a universal and efficient way to connect controllers and I / O modules of all types with a wide variety of field signals.
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The answer lies in a family of flexible interface modules designed to work with any controller and I / O platform, while providing connectivity options for all signal types (Figure 1).
A single wire harness connects the I / O of the controller to the interface module. This connection transfers a number of high density signals, typically 2 to 40, to individual points suitable for wiring to field devices. Instead of painstakingly installing individual connections, terminal blocks, and relays in a control panel, users can fabricate automation system control panels quickly and consistently in the most compact space possible, while avoiding errors.
These interface module systems are universal and work with any controller, such as those from Siemens, Allen-Bradley, Mitsubishi, Delta, Omron, Keyence, Panasonic, etc. They also work with all types of signals, so control panel designs can always use the same termination systems regardless of the controller model used.
When choosing an interface module system, designers should look for additional usability features. Modules should have provisions for clear marking and color coding to assist with precise field wiring, and they should be DIN rail mounted for flexible and reliable installation. Termination points equipped with LED status indication are particularly useful for showing operation and assisting in troubleshooting. Cables should be industrial grade, with shielded and unshielded options to support different applications. Whenever possible, I / O points should be protected against reverse polarity.
Note that the terminal block where a ground wire is laid represents the highest risk of failure, so special attention is warranted at this stage. Therefore, all terminal blocks and materials must be UL1059 recognized and IEC60947 approved.
Traditional screw terminals have been the norm for many years. Today, most users find that the new plug-in design (PID) terminal blocks are the best choice because of their more compact size, faster installation, and improved long-term reliability. High tensile strength stainless steel clip Firmly holds each wire and resists vibration, even low-frequency micro-vibration, ensuring the stability of the connection.
Example of application
A packaging manufacturing equipment supplier faced significant space constraints when installing a Mitsubishi Melsec-Q Series PLC in a control panel. The API used two 32 point I / O expansion modules and two 16 point outputs connected to the sensors and actuators of the equipment (Figure 2).
By using two signal relay interface modules and two high density with pre-assembled IDC-IDC wiring harnesses, the OEM was able to implement the most compact installation footprint possible while saving time. installation and wiring, while offering good serviceability, especially with LED indicators.
Universal Interface Modules save up to 30% panel space and reduce the need for parts inventory, as well as save up to 70% labor through the use of PID terminals.
For any equipment or industry where microcontrollers and PLCs interface with and operate field devices, there is a need for compact, flexible, universal and reliable connection solutions. Interface modules provide all of these benefits, while providing reliable and supportable connectivity.
About the Author
Matt Hou is a sales engineer for Dinkle International and has been an integral part of the development of the Dinkle Corporation subsidiary in the United States since 2018. Matt Hou holds a bachelor’s degree in electrical engineering from the University of Waterloo in Canada.