Contemporary Controls and Automated Logic Make the Pieces Fit Together

Commissioning a building automation system (BAS) is not necessarily a simple project, but it's made easier with an attached laptop doing the work.

          

 For nearly three decades, Automated Logic Corporation (ALC), Kennesaw, GA. has redefined the term "innovative" in building control, notably their WebCTRL system which uses a browser-based operator interface.

 

Although not employed during day-to-day operations, field personnel from the company's dealers utilize laptop computers to connect to the network for the startup, commissioning and troubleshooting of the BAS. A PC Card adapter, compatible with ALC's ARCNET-based ARC156 control network, would be the perfect solution for attaching to a laptop computer, but ALC had no such product. Realizing Contemporary Controls, Downers Grove, IL. was a leader in ARCNET technology in the market, Automated Logic turned their direction toward them. As early as the 1980s, Contemporary  Controls proved its expertise with the introduction of the MOD Hub series of ARCNET active hubs and ARCNET network interface modules (NIMs). It helped to establish the ARCNET Trade Association and published the ARCNET Factory Lan Primer to advance its application within the factory environment. As time past, the company began to earn a reputation for all its product lines, beneficial in both design and system troubleshooting and good service.

           

Within their ARCNET product line, Contemporary Controls had the missing PC Card adapter, the PCM20H, ALC was looking for. However, this product did not support the lower speed data rate of  the ARC156 network. Thus, Contemporary Controls agreed to take on the project to develop one to meet their requirements. Close communication between the two companies was essential for Contemporary Controls to design a medium access unit (MAU) to match the physical layer characteristics of the ARC156 in order to communicate to the control network. The result was the PCM20H-156 that is the company's standard adapter with a separate compatible MAU for the ARC156 network.

           

"It was a good move on the part of ALC," says Steve Tom, Director of Technical Information for Automated Logic. "We were able to meet our objectives through teamwork¾with everyone pulling together."

 

The Story

 

For those unfamiliar with the building automation industry, most companies just like Automated Logic, will employ an existing Ethernet backbone as the building-to-building communication network when installing a typical system. While this technology may be available in large buildings to link one floor to the next, it is seldom on hand throughout locations like mechanical rooms where HVAC controls need to be located. That type of area requires the controls contractor to install a dedicated control network. Knowing ARCNET is well-established in the industry, ALC chose ARCNET at 156 kbps for is primary control network because it's fast, reliable and economical. Let me explain why.

           

The most common data transmitted by building automation systems mainly consists of numeric and alphanumeric characters representing building conditions, historical trends, alarm conditions, etc. Although high-resolution graphics are frequently used as part of the operator interface, they are limited to the front-end computer and are not communicated throughout the building. "Thus, 156 kbps is more than fast enough for the control network," says Tom. "It's much faster than rival control networks such as MS/TP (Master-Slave/Token Passing) which typically run at 76.8, 38.4 or even 9.6 kbps. In addition to the faster data rate, ARC156 uses a communications coprocessor which relieves the main processor from the burden of having to monitor communications while executing control functions.

 

On a heavily burdened network, the actual communications throughput of the ARC156 controllers is nearly 10 times that of the previous generation 38.4 kbps controllers."

           

ARC156 is reliable. First, it's not difficult to wire it properly, and once it's wired it will operate for years with no problems. Second, ARC156 is deterministic so critical information like alarms will be communicated in less than a second. However, in non-deterministic systems, heavy network traffic, "Ethernet storms" and similar network problems can cause delays in the delivery of alarms and other critical messages.

 

Let's not forget that it's economical. ALC uses a low capacitance shielded twisted-pair wire for its control network. Tom indicated this wire is relatively inexpensive, and with it network segments can run up to 2000 feet without a repeater, allowing the installation costs to be kept low. He adds this makes the wiring costs comparable to those of slower MS/TP networks.

 

As stated previously, Contemporary Controls' designed the PCM20H-156 so it provided temporary access to the WebCTRL modules while fully supporting the 156 Kbps backplane mode operation of the ARC156 network.

 

To complete the project, ALC was faced with writing the software for Contemporary Controls' adapter. To some, writing plug-and-play software for a PC Card adapter operating in a Windows' environment is considered difficult so Contemporary Controls provided ALC with a suitable software driver for the PCM20H. By knowing the application programming interface (API), ALC was able to modify their WebCTRL software to interface to this adapter. Additionally, Contemporary Controls modified some of its ARCNET Interconnect (AI) series of ARCNET repeaters, links and hubs so that ARC156 networks could be expanded in the field: beyond the 2000 ft. limit. Some of the models support fiber optics on even longer runs. The outcome is that ALC dealers have complete flexibility in installing and maintaining ALC's ARC156 network.

 

And why the importance of compatibility with WebCTRL? "WebCTRL is our flagship system," says Tom. "As the name implies, it is designed to provide a web-based operator interface." Tom explained that a web server connected to the building automation network generates web pages which an operator can use to view and command the system from any standard web browser without the need for special software on the workstation. With WebCTRL, users can fully access and control building functions from virtually any computer or wireless device, anywhere in the world. Technicians run the WebCTRL server on their laptop and use the adapter to tie into the local ARCNET segment directly because the company runs BACnet over ARCNET, a communication protocol that enables any two devices within the BACnet system to communicate with each other.

           

Field technicians began using the adapter as soon as it was released in October of 2001. Tom says a few customers with extensive in-house service departments may benefit from this equipment, but the majority of customers will call a local dealer whenever field service is required.

           

The product consists of an adapter and a detachable medium access unit (MAU). Located on the MAU is an eight-pin mini-DIN connector that is the same type used on the WebCTRL modules. A short interconnecting cable attaches the control module to the MAU. Once attached, the laptop computer can function as the WebCTRL workstation, providing a full user interface to all control modules on the network.

           

When asked to describe the access to the network, Tom says the company provides an "access port" connection on their field hardware which is designed to be used with their APT (access port terminal) communications adapter. This APT connects the PCM20H-156 to the access port on the field hardware. Unlike the WebCTRL software, there is no special configuration required in the adapter or in the field hardware. However, the WebCTRL software has to be configured to realize it is connecting to an ARCNET segment rather than the IP backbone.

           

When installing the control system, it's not unusual for a technician to commission individual ARCNET segments. The first step physcially involves planting the control modules, sensors, actuators, etc and connect them to the HVAC equipment that they will be controlling. In this phase, it is critical that the work be coordinated among the other work being completed in the building. Here is an example cited by Tom. When a new office building is being constructed, says Tom, it's not uncommon for the mechanical room to be finished before all the ductwork and VAV boxes have been installed in the office areas. He says the control technicians are able to install controls on the boiler, chiller, and other equipment in the mechanical room, but they cannot install controls on the VAV boxes until the ductwork is installed. "The controllers in the mechanical room form their own ARCNET network segment, which for the time being, is not connected to anything else in the building." Later, when the ductwork is complete, the technicians can install controls on the VAV boxes. Chances are, the IT folks have not yet installed and activated the Ethernet backbone throughout the building, so the controls technicians will create a standalone ARCNET network segment for each floor." Often, a number of technicians will work simultaneously on the building, with one technician assigned to each floor and another technician assigned to the mechanical room to work on individual control segments, without waiting until they can all be networked together into a consolidated system leading to faster and improved service for the customer.

           

While consruction is underway, the controls engineer will write the software for this project with the criteria clearly defined. The software is comprised of computer programs, one for each controller on the project, which will execute the control algorithms needed for each individual piece of equipment. The controls engineer provides each technician the software for the control modules in his area of the building. This software takes the form of electronic files on the technician's laptop computer. Using the adapter, the technician connects his laptop computer to the ARCNET segment in his area of the building and programs the controllers; meaning he is ready to commission the system. In essence, this involves checking and calibrating each sensor which inputs data to the controller, testing each controller output to assure it activates the correct piece of equipment, and then running tests on the control software to ensure everything performs as intended. This means having the system up and operational quickly enabling the technician to meet his commitment and his deadline.

           

Once the building is up and running, the technician is able to test and diagnose the entire system. If a piece of equipment isn't functioning 100% or if it needs to be shut down or run in a specific mode for maintenance, the technician can plug into the network and control the equipment directly. This enables him to see and work on the equipment while controlling it from his laptop computer, without a need for radio communications with a second technician at a remote workstation. The technician can immediately determine the precise location of the equipment and replace or adjust it as necessary. This saves the customer time and added expense.

 

Tom adds, "Our system provides information about which ARCNET devices are on line, ARCNET reconfigurations (if any), current transmit and receive status, and the overall network bias." "I'm sure we could run more diagnostics through but's it's usually not needed."

 

To gauge how well the adapter is faring in this application, it's interesting to note what was used prior to its existence somewhat less suitable. The technicians were using an Ethernet to ARCNET router and a 24 VAC power supply to attach to a control module. They had to disconnect the existing ARCNET control wiring from the module and connect the router in its place and use and Ethernet crossover cable to join their laptop to the router. This only enabled them to talk to that one control module¾they couldn't talk across the network with this arrangement. When they were finished, they had to disconnect the hand-carried router and connect the module back into the ARC 156 network.

 

As another option, technicians used long lengths of CAT-5 cable and repeaters as necessary to try and bring and Ethernet port into the mechanical room, next to the equipment they were trying to commission. Now, they could talk to the equipment through the WebCTRL server, assuming the server and the rest of the network was operating properly. Occasionally, they tried wireless Ethernet connections instead of CAT-5 cable. Tom emphasizes that while this worked in some situations, given the distance limitations of both wired and wireless Ethernet segments, it was far from a satisfactory solution.

 

It came to no surprise that ALC's reaction to working with Contemporary Controls was  positive. Tom says the company worked side-by-side in developing this product to meet their dealers's requirements. Its ease-of-use alone has resulted in a definite reduction of time and effort on the part of their dealers' field technicians.

 

Tom was pleased to do business with a smaller company, a company that still provides the personal touch engineers that give quick response to development needs a technical support team that makes the customer feel confident in understanding his problem to shipping products to meet a customer's schedule.

 

This entire approach of working as one was a competitive advantage for both companies. It brought together the talents of everybody in making decisions resulting in a product that met the needs of two company's customers.

 

This article is provided by Contemporary Controls, written by Debra Biela.  Contemporary Controls builds on 27 years of design and manufacturing experience with network interface modules, wiring hubs, repeaters, bridges, routers, gateways and analyzers--all with defined life cycles and long-term availability. For more information on Contemporary Controls, please visit their website at: http://www.ccontrols.com.