Figure 1 - Large in-ground wedge barrier systems can stop a 65,000 lb truck traveling at 50 mph. Converting such a system from hardwired hydraulic operation to electric actuators and PLC controls makes them cleaner, more reliable, and easier to maintain.

K12 Defense quickly converts vehicle barriers from messy hydraulics to clean PLC-controlled electric operation.

Military bases, embassies, government buildings and airports around the world are protected by hydraulically-operated vehicle barriers (Figure 1) that prevent terrorists from crashing through gates and entering the grounds with trucks or autos loaded with explosives. These barriers are primarily hydraulically operated and controlled by basic hardwired relay logic.

Hydraulic operation makes the barriers difficult to maintain as they often leak hydraulic fluid, and specialized contractors are required for service and repairs. Hardwired relay logic control is inflexible, provides no diagnostics, and is prone to failure.

At K12 Defense Consultants in Mesa, AZ, we specialize in retrofitting existing vehicle barrier systems—converting them from relay-controlled hydraulic operation to Programmable Logic Controller (PLC)-controlled electric operation. The benefits of these retrofits are summarized in Tables 1 and 2, and detailed below:

 

TABLE 2

More reliable.

More control functions available.

PLC can communicate with other systems.

PLC can keep records of alarms and events.

PLC programming is easily modified and inputs/outputs easily expanded.

PLC provides detailed operational/troubleshooting diagnostics.

PLC provides detailed operational/troubleshooting diagnosticsThe conversion is made possible because of powerful servo actuators which are capable of replacing hydraulic cylinders, and because of compact, rugged industrial PLCs from Phoenix Contact. Within a matter of one to two days, we can convert an existing barrier system from relay-controlled hydraulic to PLC-controlled electric operation.

Stopping Terrorists Electrically  

Figure 2: Drop Arm barriers can stop a 15,000 lb truck traveling 50 mph.

Barriers prevent unauthorized vehicles from entering secure areas where personnel, equipment, or buildings could be harmed.  For example, if terrorists were allowed to drive a truck bomb onto an Air Force flight line they could do significant damage to aircraft and armaments, not to mention the risk to personnel in that area. Another example is protecting underground parking areas located beneath courthouses and other government facilities.

 

Many military bases, airports, and similar facilities worldwide have installed vehicle barriers—only to find that the hydraulic systems tend to leak hydraulic fluid, causing environmental problems, and are difficult to maintain and repair. In many cases, required specialized maintenance is beyond the capabilities of the facility, forcing the facility to contract those services to outside specialists at a very high cost.

The entire system could be replaced with new electrically operated barriers, but replacement is a huge project as barriers are dug in and cemented in place. Installing a barrier is a big job, and so is removing one. If a facility has an existing barrier in place with operational problems, it’s very expensive to remove it and replace it with a new barrier. The roadway will also be out of commission for two to four weeks during the replacement. Converting barriers, instead of replacement, is a much better option as it costs less money, can be completed in one to two days, and results in a superior system.

 

When we convert a vehicle barrier, we first replace the hydraulic cylinders with electric actuators. (See the Sidebar: “How to Stop Terrorists,” for a description of the three basic kinds of vehicle barriers).

For large, in-ground “wedge” barriers (see Figure 1), we replace the hydraulic cylinders normally used to raise the barrier plate with servo linear actuators capable of producing 16,000 lb of thrust.  These actuators, custom engineered for us by Moog, have very powerful integrated springs which reduce the amount of electrical power needed to raise the barrier and extend the mechanical life of the actuators. All the previously required hydraulic hardware is eliminated and replaced with electric actuators and a new electrical control cabinet. 

Smaller surface-mount wedge barriers do not require as much force to raise the barrier plate, so a gear motor system is used to replace the hydraulic cylinders. A gear motor, a mechanical linkage, and a small electrical control cabinet replace all of the hydraulic components.  

Figure 3: In a retrofit, an electric linear actuator replaces the hydraulic system of a drop arm barrier.

After the hydraulic cylinders have been replaced, we convert the controls. Most hydraulic control systems use a hardwired relay circuit board or hardwired relay logic. Hardwired control logic doesn’t allow intelligent operation of the barrier and traffic signals, and has very little flexibility regarding barrier operation. Hardwired logic also doesn’t provide any troubleshooting diagnostics or a record of operations. To improve the control system, we replace all of the hardwired hydraulic control circuitry with a PLC from Phoenix Contact.

The PLC allows for better control of the barrier and associated traffic signals (see Sidebar: “PLC as Traffic Cop”). It also provides troubleshooting diagnostics, and a time and date stamped record of barrier operations. The PLC’s program can be easily modified to provide the exact operational features desired at each installation.

Phoenix Contact PLCs and other electrical components were selected because of their industrial robustness, extended temperature operating range, and overall quality. The two-port Ethernet switch built into each PLC, along with Web server and FTP server capabilities, provide the communication options and connectivity that our clients need.

The conversion to electric from hydraulic requires a new electrical control cabinet (Figure 4) to house the components necessary to power and control the electric linear actuators. Because this new control cabinet requires more electrical components than the hydraulic system, it must be built in a compact manner to fit within the existing barrier enclosure. DIN rail mount Phoenix Contact terminal blocks, relays, circuit breakers, power supplies, and a PLC are used to minimize space requirements.   

Figure 4: The control cabinet contains a Phoenix Contact PLC, terminal blocks, relays, circuit breakers and power supplies along with other required components. All of these components fit into the same space as the old hydraulic controls.

A small electrical enclosure is used as an interface box to make the transition from the existing control wiring that is already in the barrier enclosure to the new control cabinet wiring. This interface box eliminates the need to run existing wires all the way to the new control cabinet, an important advantage as many of the existing wires wouldn’t be long enough and would have to be spliced.  

Insulation displacement terminal blocks are used for connecting the existing wires in the interface box. A large range of wire gauge sizes can be accommodated by these terminal blocks and no stripping, crimping, or screw tightening is required to make the connections. We just stick the unstripped wire into the terminal block hole and operate the connecting lever mechanism with a small screw driver. These connections will not loosen from vibration or heat, and these terminal blocks save significant time on-site during installation. 

Phoenix Contact Relay assemblies snap onto the DIN rail and are only 1/4-in. wide. Each has an LED indicator. A suppression diode is built in across the coil, eliminating the need to add and wire external suppression diodes. Each relay is available with mechanical contacts or a solid state output, and each relay can be popped out and replaced without disconnecting wires or removing the relay base from the DIN rail. Jumper strips allow adjacent relays to be wired to the same voltage source without connecting individual wires to each relay. 

System circuits are isolated from each other through the use of circuit breakers. This allows the main components of the system to keep operating when a less critical circuit, such as one providing power to a ventilation fan or an indicator light, trips out. The Phoenix Contact DIN rail mount circuit breakers are compact and provide a switch which indicates the state of the breaker and allows each to be individually turned off.  They also have a provision to be jumpered together, thus eliminating the need to wire each circuit breaker power input individually when they are supplied from a common source.

The Phoenix Contact Quint SFB 24 Vdc power supply is used because of its wide temperature range, 50 percent boost power capability, and overall reliability. The power supply ensures that circuit breakers trip when overloads occur because it can supply up to six times nominal current for a short duration. This guarantees that the entire barrier system doesn’t malfunction when a non-critical circuit is overloaded. An optional battery backup system allows the barrier and traffic signals to function normally if AC power to the power supply is interrupted, further reducing barrier down time.

The PLC controls all of the devices required for the barrier system. The PLC’s inputs and outputs are expandable and can be tailored to match the individual requirements of each barrier application. Besides controlling the barrier, traffic signals, and other auxiliary devices, the PLC records operational data and diagnostic information. 

Figure 5: Any PC with an Ethernet port and a web browser can display screens from the PLC.

The PLC also records all of the barrier activities to a CSV file, with each activity time and date stamped. The FTP server capabilities of the PLC allow any computer with web browser software to retrieve the time and date stamped data file. The file can them be displayed, filtered, and sorted using Excel or another spreadsheet program. Multiple PLCs can easily be connected together into a local area network because each PLC can function as a two-port Ethernet switch.   

The installed electrically-operated and PLC-controlled systems have operated as planned and added features to barriers that were lacking before the retrofits. Reliability has been improved and maintenance has been reduced over the original hydraulically operated systems and their corresponding hardwired control circuitry. In the future, we expect that many new barrier systems will be supplied with electric actuators controlled by a PLC.