Electricity: conductors and insulators – Boxes and housings – With electrical device
Reexamination Certificate
2000-03-31
2001-12-18
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
With electrical device
C439S703000, C174S064000
Reexamination Certificate
active
06331674
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a terminal block for connecting both increased safety rated circuits and intrinsically safe rated circuits. More particularly, this invention relates to a terminal block inside a housing that connects both increased safety rated circuits and intrinsically safe rated circuits. Still more particularly, this invention relates to a terminal block that allows the housing to be opened by physically enclosing the increased safety rated circuits inside an enclosure in the housing to prevent arcing with the intrinsically safe circuits.
Problem
It is common for electronic circuits to be used in hazardous environments. Hazardous environments are environments containing volatile material that could be ignited by heat or sparks from electronic circuits. Some examples of volatile materials are gases such as hydrogen. Since electronic circuits must be used in these environments, several regulatory agencies such as the UL in the United States, CENELEC in Europe, CSA in Canada, and TIIS in Japan rate the electronic circuits for use in these hazardous environments. The rating of electronic circuits requires the housing around the circuits prevent the electronic circuits from igniting the volatile material.
One such rating for electronic devices is intrinsically safe. An intrinsically safe circuit is a circuit that operates under a certain energy level. The certain energy level is low enough to assure that the circuit cannot generate a spark or enough heat to ignite the volatile material.
A second such rating is increased safety. An increased safety circuit operates at a higher energy level than an intrinsically safe circuit. However, an increased safety circuit still has many safety features to prevent arcing in the circuit.
It is a problem that when circuits having different ratings are used in the same environment that the circuits must remain separate to maintain the ratings. For example, if an increased safety rated circuit is used in the same hazardous environment as an intrinsically safe circuit, the increased safety circuit must be physically separated from the intrinsically safe circuit in order for the intrinsically safe rating. The maintenance of the safety rating may be important to allow the intrinsically safe circuit to be kept in a less protective housing.
One system in which two differently rated circuits may be in a hazardous environment is a Coriolis flowmeter. A Coriolis mass flowmeter measures mass flow and other information of materials flowing through a pipeline in the manner described by U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. A Coriolis mass flowmeter has one or more flow tubes of a curved or straight configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors are placed at two different points on the flow tube to produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the sensors is calculated in units of time. The phase difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
The sensors transmit the sinusoidal signals to a signal conditioner. The signal conditioner generates parameter signals that indicate properties of the material flowing through the flowmeter. The signal conditioner also generates a drive signal applied to the driver to vibrate the flow tubes. The parameter signals are then transmitted to a host system which provides the desired properties to a user.
In this system, power supplied to the host system is so great that the circuit receiving the power can only be increased safety rated. However, the processor and the signal conditioner may be operating at a low enough power level to be rated as intrinsically safe. Therefore, a terminal block for connecting power and a secondary processor to the host system require physical separation of the power from the other circuits.
Solution
The above and other problems are solved and an advance in the art is made by the terminal block housing of this invention. One advantage of this invention is that the increased safety rated circuits are separated from the intrinsically safe circuits. A second advantage is that the housing may be opened as the increased safety rated circuits are covered to maintain the physical separation when the housing is opened. A third advantage of this invention is that a cover over terminals for the increased safety rated terminal may be opened to inspect the terminals.
In accordance with this invention, an explosion proof terminal block housing for connecting intrinsically safe rated circuits and increased safety rated circuits is made in the following manner. A housing encloses an area. Inside the housing, there are openings through a first surface at a first end of the housing. A first set of conductors for connecting intrinsically safe rated circuits are connected to terminals inside the housing and extend through the openings.
A second set of conductors for connecting increased safety rated circuits are connected terminals in the housing and extend through the openings in the first surface. A wall extending upward from the first surface between two sides of the housing separates the terminals of the first set of conductors from the terminals of the second set of conductors. A cover over the second set of conductors extends from a top side of the wall substantially to a side of the housing to enclose the second set of conductors inside the enclosed area. The wall and cover physically enclosing the increased safety circuit to allow the housing be opened.
The terminal block housing may also include an opening in a second end of the housing and a lid mated to the opening to enclose the housing. The lid and sides inside the housing may include threading on the lid to mate the lid to the opening. The threading allows the housing to be opened while maintaining a flame path when closed to remain explosion proof.
The cover may have a first edge coupled to a top side of the wall. A coupling allows the cover to be moved to expose said second set of conductors. A locking mechanism may prevent the cover from being moved to keep the second set of conductors enclosed. The coupling may be a hinge on a top side of the wall and a first edge of the cover to affix the cover to the wall. The locking mechanism may be a captive pin that fits though an opening in the cover and affixes to an opening on a bottom side of the cover to lock the cover in place. The first surface of the housing may also have unshaped walls extending outward from the first surface to enclose each of the first set of conductors on three sides.
In another aspect of this invention, the terminal block inside the housing has a molding having a base with a first surface that has molding defining unshaped walls and the wall extendin
Samson Allan L.
Zolock Michael J.
Chrisman Bynum & Johnson, P.C.
Micro Motion Inc.
Patel Dhiru R
Reichard Dean A.
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