Weigh In Motion System

Overview of Weigh In Motion Systems

The Weight In Motion systems (WIM) operate on municipal roads, federal highways and bridges. Reliability is necessary to ensure safety of drivers by keeping roadways from overstress, vehicles entering and exiting to weigh stations and the cost of the weigh station itself. With the growing demand and more equipment is being inserted into the remote cabinets, they are very susceptible to damaging overvoltages resulting from lightning strikes and switching transients.

Threat to WIM Systems

These are exposed applications that face a very significant threat from direct (conducted) and indirect (induced) effects from lightning strikes. The damage can be caused by a variety of source transients which affect sensitive components within the cabinet and connected in the network. As a result of the disconenction of vital equipment, places drivers, roads and critcal operations are placed at risk. It is important to develop a surge mitigation strategy like the box concept. Simply draw a box around the roadside equipment cabinet and any wire that enters or exits the box is vulnerable to transient surges. Place a Surge Protective Device (SPD) at each vulnerable point to ensure equipment is safe and protected.

WIM Sensor

The solution for Weigh In Motion Systems

CITEL recommends the use of parallel SPDs for the AC input, to ensure that once the SPD reaches the end of life scenerio it will not cause a power loss and thus keeping equipment connected. This reduces the risk of down-time resulting in loss of revenue and frustration among users. Surge protection plays a vital role in preserving the integrity of equipment and, more importantly, protecting the lives of personnel.

The installation of Surge Protective Devices (SPDs) within the Roadside Equipment Cabinet is a measure that will not only extend the life of the circuit components but also increase the reliability of the system as a whole.

Selecting an SPD for Weigh In Motion Systems (WIM)

NEC/NFPA 70 require that Surge Protective Devices (SPDs) shall be UL1449 Listed . This means selecting a surge protector is easier than it has ever been. There are only a few choices available for SPDs that are UL Listed for any of the most commonly used surge standards including UL1449 5th Edition, UL497B, and UL497E, in addition, only UL Listed Surge Protectors are acceptable for facilities that will install a Lightning Protection System (LPS) certified to either NFPA 780 or the UL96A Master Label.

Recommended SPD for Main Service Panel

Location	Equipment	System	Surge Protector Model#	Link
	Main Service Panelboard	120/240Vac	M50-120T-A

Recommended SPD for Roadside Equipment

Location	Equipment	System	Surge Protector Model#	Link
	Roadside Equipment Panel	120Vac AC Input	DS72US-120S/G-F-ASSM
	Power Supply	120Vac AC Power Input	DS72US-120S/G
		24Vdc DC Power Output to Data Logger	DS220S-24DC
	Ethernet Switch	Ethernet Cat 6A	MJ8-C6A
	Vehicle Detection Camera	POE+	MJ8-POE-C6A
	Serial Interface Unit (SIU)	24V	DD25-24V

References