The present relates generally to parking meters and, more particularly, to a parking meter with a grounding arrangement for reducing corrosion effects due to electrolysis.
A typical parking meter includes a housing for a meter operating mechanism, i.e., a meter head, connected to a vault for receiving coins and/or credit cards and/or debit cards. The vault is secured to the top of a hollow pole having a lower end usually embedded in a concrete structure, e.g., a footing or a concrete sidewalk. The vault is secured to the pole by a spider having radially extending legs bearing against an interior wall of the pole. A steel bolt is threaded into a central opening of the spider and extends through a hole in a base at the bottom of the vault. A steel mounting plate having a central, threaded bore secures the bolt to an interior face of the base of the vault. The bolt, mounting plate and spider secure the vault to the pole. In some meters, the vault and head are made of cast iron. In other meters, the vault and housing are made of cast Zamac, an alloy of zinc and aluminum. The head and vault are usually made of the same materials but some are made of a combination of cast iron and cast Zamac, such that, in some meters the vault is made of cast iron and the head is made of cast Zamac, and in other meters the vault is made of cast Zamac and the head is cast iron.
To enhance the life and appearance of the vault and housing, the cast iron vault and housing can be covered with hot dipped galvanized steel coatings, in turn covered by non-epoxy thermosetting electrically insulating organic powder coatings, as disclosed in my co-pending, commonly assigned application, Ser. No. 08/841,724, filed Apr. 24, 1997, entitled xe2x80x9cHousing for Parking Meters and Other Outdoor Token Handling Devices and Method of Making Same.xe2x80x9d
In actual field tests of cast iron parking meters having such hot dipped galvanized and organic powder coatings and of Zamac meters, it was found that corrosion originated at the intersection of the vault and the steel mounting plate and spread to the head and pole. I have determined that the corrosive effects, which are the greatest when the parking meters are in salt water laden air, as at the seashore, and/or in meters having dissimilar metals at the contacting surfaces of the mounting plate and vault base, are due to electric current flowing in response to an electrolysis effect between the contacting metal surfaces. The electrolysis effect is due to salt water ions penetrating the vault and/or the effects of the electrochemical (i.e., electromotive) series potential differences between the different metals at the contacting surfaces; for example, the mounting plate and bolt extending through it are typically steel, while the vault base is cast iron or Zamac.
It is, accordingly, an object of the present invention to provide a new and improved parking meter having a structure for reducing the effects of corrosion, particularly in environments where the parking meter is subjected to salt water laden air.
In accordance with the present invention, a parking meter includes a metal structure electrically and mechanically connected to a region of the meter where corrosion tends to occur. The metal structure is also inserted into the earth in the vicinity of the parking meter. The region is where first and second parts have contacting metal surfaces such that corrosion tends to occur at and in the vicinity of the region in response to electrolysis induced electric current having a tendency to flow between the contacting metal surfaces. The metal structure shunts to the earth the current having a tendency to flow between the contacting metal surfaces.
In the preferred embodiment, the parking meter first part is the vault for receiving tokens or credit or debit cards, and the second part is the mounting plate.
The metal structure includes (1) a metal rod extending through the pole and the concrete structure into the ground, (2) a second metal mounting plate at the region, and (3) a metal wire mechanically and electrically connected between the second mounting plate and the metal rod so it extends between legs of the spider. The metal rod, wire and second mounting plate are preferably made of the same high electric conductivity metal, e.g., aluminum, to provide a high conductance electric shunt between the region where corrosion tends to occur and the earth. Because the metal rod, wire and second mounting plate are preferably made of the same metal, electrolysis does not tend to occur between the intersecting surfaces thereof. The second mounting plate is preferably secured in place by the spider attachment bolt, the mounting plate and the interior face of the vault base.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed descriptions of a specific embodiment thereof, especially when taken in conjunction with the accompanying drawings.