Patent Application
20160233633
Not Applicable.
Not Applicable.
Not Applicable.
This invention relates to process control instruments, and more particularly, to a removable and rotatable, multi-pin explosion proof connector.
Process control systems require the accurate measurement of process variables. Typically, a primary element senses the value of a process variable and a transmitter develops an output having a value that varies as a function of the process variable. For example, a level transmitter includes a primary element for sensing level and a circuit for developing an electrical signal proportional to or representing sensed level.
Knowledge of level in industrial process tanks or vessels has long been required for safe and cost-effective operation of plants. Many technologies exist for making level measurements. These include magnetostrictive, capacitance, ultrasonic and microwave radar, to name a few.
One form of process instrument is of the intrusive type in which the primary element is in direct contact with the process fluid for sensing level. A magnetostrictive transmitter is an example of an intrusive type level measurement instrument. A magnetostrictive transmitter has a probe including a magnetostrictive wire maintained under tension in a tube. The probe extends into the process vessel. A magnetic float is movable proximate the probe and floats atop the fluid in the vessel. An electrical pulse is transmitted on the magnetostrictive wire. The electrical pulse interacts with the magnetic field of the float, which creates a torque on the wire to produce a torsional force on the wire, thus initiating a torsional wave that propagates along the wire at the speed of sound. This is known as the Wiedemann effect. Typically, a pickup sensor is positioned at one end of the wire to sense the torsional wave on the wire. The elapsed time is measured between the launch of the electrical pulse and the signal from the pickup sensor. The distance between the magnet and the pickup sensor is calculated from the measured elapsed time multiplied by the speed of the torsional wave, representing level.
It is often desirable to rotate the transmitter or other electronics head for ease of viewing of the display or accessing wire compartments or the like. Also, it is advantageous to have the transmitter removable for ease of installation and maintenance. In hazardous environments it is necessary that connection between the transmitter and probe satisfy requirements for explosion-proof applications.
This application is directed to improvements which allow a transmitter to be rotatable, removable and/or remote mountable.
In accordance with one aspect there is disclosed a process measurement instrument comprising a process adaptor for mounting to a process vessel or the like and operatively associated with a sensing element for sensing a process variable and including plural electrical conductors. An instrument housing includes a control circuit. A connector assembly is operatively disposed between the instrument housing and the process adaptor for removably connecting the instrument housing to the process adaptor. The connector assembly comprises a first connector including a cylindrical connector body having an offset boss with a first multi-pin wire connector. A second connector includes a cylindrical connector housing, receiving the cylindrical connector body, having an offset bore, receiving the offset boss, and having a second multi-pin wire connector, mateable with the first wire connector, for selectively electrically connecting the control circuit to the sensing element with the offset boss and offset bore ensuring proper alignment of the first and second multi-pin wire connectors.
It is a feature that the cylindrical connector body comprises a one piece metal body threaded at one end, opposite the offset boss, for connection to the process adaptor or the instrument housing.
It is another feature that the cylindrical connector housing comprises a one piece metal housing. The connector housing may include a neck at one end and a cylindrical swivel secured for rotation around the neck. The swivel includes an outer thread for connection to the process adaptor or the instrument housing and enabling rotation of the control housing relative to the process adaptor. The swivel may include a pin receivable in an arcuate slot in the cylindrical connector housing to limit rotation of the cylindrical swivel. The swivel may include a set screw engaging the neck to selectively prevent rotation of the cylindrical swivel.
It is another feature that the second connector is adapted to provide a cylindrical flame path between the cylindrical swivel and the neck and the cylindrical connector body and the cylindrical connector housing are adapted to provide a second cylindrical flame path to provide an explosion-proof connector assembly.
It is another feature that the neck comprises a through opening filled with a potting compound and the cylindrical connector body includes a through opening filled with a potting compound.
It is yet another feature to provide an elongate cable including a third connector, similar to the first connector, at one end, and a fourth connector, similar to the second connector, at an opposite end. A cable is connected between the first and second connector to remotely mount the control housing relative to the process adaptor.
It is an additional feature to provide an O-ring disposed between the cylindrical connector body and a cylindrical connector housing.
It is yet another feature to provide a lock screw receivable in an opening in the cylindrical connector housing engaging the offset boss to secure the second connector to the first connector.
There is disclosed in accordance with another embodiment a process measurement instrument comprising a process adaptor for mounting to a process vessel or the like and operatively associated with a sensing element for sensing a process variable and including plural electrical conductors. An instrument housing includes a control circuit. A connector assembly is operatively disposed between the instrument housing and the process adaptor for removably connecting the instrument housing to the process adaptor. The connector assembly comprises a first connector including a cylindrical connector body with a coaxial through opening and having an offset boss at one end with a first multi-pin wire connector in the through opening at the offset boss and a first electrical cable in the through opening connected to the first multi-pin wire connector. A second connector includes a cylindrical connector housing with a coaxial through opening and a first blind bore at one end, receiving the cylindrical connector body, and an offset blind bore in the first blind bore, receiving the offset boss. A second multi-pin wire connector is in the offset blind bore and extends into the through opening. A second electrical cable in the through opening is connected to the second multi-pin wire connector. Incident to the offset blind bore receiving the offset boss, the first multi-pin wire connector is mated with the second multi-pin wire connector for selectively electrically connecting the control circuit to the sensing element with the offset boss and offset bore ensuring proper alignment to the first and second multi-pin wire connectors.
Other features and advantages will be apparent from a review of the entire specification, including the appended claims and drawings.
Referring to
The instrument 20 includes a transmitter 22 and a probe 24 connected by a connector assembly 26. A magnetic 28 (usually part of a float) is receivable on the probe 24. The transmitter 22 includes a control housing 30. The housing 30 comprises a dual compartment instrument housing as described in Mulrooney et al. U.S. Pat. No. 6,062,905, the specification of which is incorporated by reference herein. The housing 30 houses a sensing circuit, described below, for determining level and generating an electrical signal representing level for transmission to other control instruments, as is well known. A process adaptor 32 is provided for mounting to a process vessel or the like and is operatively connected to the probe 24. The process adaptor 32 may take any known form, such as a flange or threaded connector, as is conventional. As described herein, the connector assembly 26 is operatively disposed between the instrument housing 30 and the process adaptor 32.
The connector assembly 26 is rotatable, as illustrated by comparing the orientation of the control housing 30 in
The magnet 28 comprises a conventional magnetic float, and is illustrated schematically. The magnet 28 is effectively captured on the probe 24. As is known, the magnet, in the form of a float, floats atop the material the level of which is being sensed and creates a magnetic field representative of the location of the top surface of the fluid or other material. As is apparent, the magnet 28 could be replaced by another type of magnetic device for more generally sensing position of the magnet. Thus, the sensing instrument 20 could alternatively sense position rather than level.
Referring to
The sensor crystal assembly 68 is electrically connected to a preamplifier circuit 70 of the probe circuit 60. The probe circuit 60 also includes a memory circuit 72. The memory circuit 72 is provided with a write protect function.
The transmitter 22 includes a control circuit 74. The control circuit 74 is connected via the connector assembly 26, as described below, to the probe circuit 60. The control circuit 74 comprises a controller in the form of a programmed microcontroller 76. The microcontroller 76 comprises a programmed processor and associated memory and I/O, such as a keypad and display (not shown), for operating in accordance with a control program to control operation of the instrument 20.
The connector assembly 26 connects a multi-conductor cable 78P from the probe 24 to a multi-conductor cable 78T from the control circuit 74. These cables 78T and 78P include eight connector lines labelled A, B, C, D, E F, G and H.
The microcontroller 76 includes DRIVE+ and DRIVE− outputs connected via connector lines A and B to the drive circuit 66. A signal output from the preamp circuit 70 is connected via the connector line C to a signal output line of the microcontroller 76. The microcontroller 76 includes probe memory interface ports connected via connector lines D and E to the memory circuit 72. Connector lines F and G are provided for plus voltage and ground, as illustrated. The swivel connector 26 illustrates a dashed line, representing a connector line H, used for a write protect input of the memory circuit 72. This line H is only used during a factory calibration function, as described below, and does not connect to the microcontroller 76.
As is conventional, the microcontroller 76 controls the drive circuit 66 to develop an electrical pulse on the magnetostrictive wire 61. A magnetic field from the float 28 produces a torsional wave on the magnetostrictive wire 61 sensed by the sensor crystal assembly 68. This wave is used by the microcontroller 76 to determine position of the float 28, or more generally, the magnet, representing level when implemented as a level measuring instrument.
The illustrated embodiment comprises a process measurement instrument in the form of a magnetostrictive instrument which can be used to sense position of a magnet. In the illustrated embodiment, the magnet would float atop material level to indicate level. However, the connector assembly described herein is not limited to a magnetostrictive type sensor or a level sensor. The connector assembly 26 could be used with other process measurement instruments including a sensing element for sensing a process variable and plural electrical conductors in a sensing element for connection to a control circuit in a separate control housing. Examples of other type devices include capacitance, guided wave radar, ultrasonic and microwave radar, to name a few. This application is not directed to the specific control technology, but rather the use of a connector assembly for connecting an instrument housing to the sensing element.
Referring to
Referring to
A first multi-pin wire connector 126 is receivable in the through opening 106 and is flush mounted in the boss 120. In the illustrated embodiment, the wire connector 126 comprises a plastic body having eight pins for connection to the eight lines of the cable 78P, as will be apparent. A potting compound 128 fills the through opening 106, below the wire connector 126, see
Referring to
Referring also to
A second multi-pin wire connector 150 is partially receivable in the through opening 136 and extends into the offset blind bore 148 flush with the shoulder 146. As such, the second multi-pin wire connector 150 is coaxial with and aligned with the first multi-pin wire connector 126, as illustrated in
The swivel 132 comprises a collar 152 having an outer thread 154. The collar 152 provides a mechanical connection to the control housing 30 or the process adapter 32, depending on the orientation of the connector assembly 26. The collar 152 is receivable on the neck 140. A pair of O-rings 156 and 158 are provided therebetween. A rectangular ring 159 at a top end 160 of the neck 140 retains the swivel 132 on the neck 140. A roll pin 162 extending from the swivel 132 is receivable in an arcuate groove 164 in the housing shoulder 138 to limit rotation of the swivel 132 relative to the connector housing 130. A locking set screw 166 through the collar 152 selectively engages the neck 140 to lock the swivel in a desired position relative to the connector housing 130.
To prevent damage to the plastic wire connectors 126 and 150, the connectors 100 and 102 must be aligned before the wire connectors 126 and 150 begin to interlock during insertion. This is accomplished using the offset boss 120 in combination with the offset bore 148. The connectors 100 and 102 are illustrated disconnected in
A pair of locking set screws 168 and 170 extend into the offset bore 148, see
As with the first connector 100, a potting compound 72 fills the second through opening 136 above the second wire connector 150. Thus, the wires 78T and 78P are encapsulated with an approved flame retardant potting compound. Also, a cylindrical flame path FP1, see
As described herein, the transmitter 22 is selectively removable from the probe 24. This is done using the connector assembly 26 which enables the transmitter 22 to be removed from the probe 24, see
Particularly, the connector assembly 26 using the first connector 100 and the second connector 102 enables the control housing 30 to be removed from the process adaptor 32 and thus the probe 24 for servicing and the like. Also, the use of the swivel 132 allows the connectors 100 and 102 to be rotatable relative to one another to provide a desired orientation of the control housing 30. Moreover, a cable 34, see
It will be appreciated by those skilled in the art that there are many possible modifications to be made to the specific forms of the features and components of the disclosed embodiments while keeping within the spirit of the concepts disclosed herein. Accordingly, no limitations to the specific forms of the embodiments disclosed herein should be read into the claims unless expressly recited in the claims. Although a few embodiments have been described in detail above, other modifications are possible. Other embodiments may be within the scope of the following claims.
