Over the past several years, the networking of drives has gone through several
phases of evolution. Today, web-enabled Eth...
In addition to the issues above, any computer that is going to use or display this
information must be specially configure...
drive, meaning that the user can access it with nothing more than a browser such as
Internet Explorer or Netscape Navigato...
With this type of a display, the user can instantly see the effect that variable changes
are having on the overshoot and d...
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Web Enabling Variable Frequency Drives

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Web Enabling Variable Frequency Drives

  1. 1. Over the past several years, the networking of drives has gone through several phases of evolution. Today, web-enabled Ethernet communications represents the latest, and most powerful, of all of these phases. The level of control and the amount of information available are significantly improved over earlier methods. Most importantly, with web-enabled Ethernet, the ease of both getting information and displaying it is on an entirely new level than was possible with older technologies To help in understanding the power of this new development, the earlier phases could be broken down as follows: Phase One - Network connection to an intelligent device. The intelligent device (such as a PLC or a Building Automation System) would talk to the network, and then it would "communicate" with the drive via traditional dry contacts and proportional signals (4-20mA, 0-5VDC, 0-10VDC). In basic systems, the system only told the drive what to do, as if it were a mechanical actuator like the damper controls and valves that the drive replaced. In more sophisticated systems, the drive would feed back some information, such as dry contact closures for drive status (i.e.: power status, run status, fault status) or proportional signals (i.e.: for speed confirmation, motor amperage, or motor kW) Phase Two - Network connection to the drive - one way communications. The drive is directly connected to a serial network such as Modbus, FIPIO, N2, etc. and is used for control only. The network simply tells the drive to turn on or off and how fast it should go when it is on. Phase Three - Network connection to the drive - two-way communications. The drive does all of the control described above. The link is also used for monitoring the status of the drive or for reading data (i.e.: fault logs, variable states) to aid in troubleshooting the drive in the event of a fault. Sometimes this link is used to re-program or tune the drive. All of these phases require special software, special network knowledge, and special wiring for the network involved. For example, the wiring, junctions, and terminations of Modbus are quite different from that of ControlNet. Technicians that support such equipment must be trained in all of these areas.
  2. 2. In addition to the issues above, any computer that is going to use or display this information must be specially configured for the software and network connection. Anyone using the software will need specific training on how to use it. In order to create a graphical display even more technical software is required. The next step in the network evolution is to make all this detail transparent to the typical user. That is what web-enabled Ethernet is all about. There are many advantages to using Ethernet. The simplicity of the "Ethernet" part of this concept, the network, is the first benefit. Each of the standard industrial control networks has it's own wiring and addressing peculiarities that require training. Any implementation issues associated with Ethernet are all well understood by the IT department of any company or facility. There have been many debates about the relative levels of determinism between older industrial control networks and Ethernet, but it is fairly well understood today that this is a function of how an Ethernet network is switched and not of the network itself. The second advantage to this approach revolves around the "web-enabled" part of the concept and is even more significant. Pure data by itself is not meaningful if it is simply sitting in the data registers of a Drive or a PLC. If that data can be put into the proper context, something interesting happens. Data evolves into Information and Information evolves into Knowledge. The communications link goes from being a simple control network to being a true HMI that anyone can use. For a long time, there have been a number of HMI packages and Drive control programs that provided this function. The software would display information in a meaningful manner and make the programming of the drive much easier than using a keypad. Because such software had to run on dedicated computers, configured for and wired to, the specific industrial control network involved, the usability of this software is limited. With a web-enabled Ethernet connection, a Drive can provide the HMI functions as well as a superior programming capability without any special software running on the computer involved. The software is resident on the communications card in the
  3. 3. drive, meaning that the user can access it with nothing more than a browser such as Internet Explorer or Netscape Navigator. As an added advantage, this connection will work from anywhere that the user can connect to their own intranet. If a user is inside of their corporate firewall and has the correct addresses and passwords, they could monitor and control a Drive in San Francisco from a computer in France. Some advantages of web-enabled Ethernet for Drives are simplified wiring and software, but there are even more benefits available as the concept evolves. To illustrate this, the tuning of a PI loop could be considered. To many people that work with Drives, tuning a PI or PID loop is almost more of an art than a science. Doing such tuning just based on data is very challenging and needs a high level of expertise. In a typical example of a simple loop, there is a Drive controlling a fan that feeds into ductwork in an HVAC system. There is a pressure sensor in the duct and the drive is configured to maintain a set point using PI control. Using web-enabled technology, a screen can be setup in the drive to provide a real time plot of both the set point and the feedback signal for a Drives control scheme. The screen would also provide tools for setting up the various PI control variables. An example of such a screen from an actual system using simple Java beans for the display is shown below
  4. 4. With this type of a display, the user can instantly see the effect that variable changes are having on the overshoot and dampening of the system. The time required to tune the system is sharply reduced and the user has a much better feeling for what is going on. All of this is done with nothing more than a web browser and no special software running on the computer. Web-enabled Ethernet represents a significant advance in the control and operation of Variable Speed Drives. The advantages that this technology offers users will lead to fundamental changes in the use of communications with Drives.

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