CN1155329A

CN1155329A - Transmitter with water draining housing and improved method of mounting RFI filter

Info

Publication number: CN1155329A
Application number: CN 95194577
Authority: CN
Inventors: 约翰·D·约翰森; 威廉姆·R·柯克帕特里克
Original assignee: Rosemount Inc
Current assignee: Rosemount Inc
Priority date: 1994-08-11
Filing date: 1995-08-01
Publication date: 1997-07-23

Abstract

A transmitter (100) transmitting a sensed process variable over a conductor (134A, 134B) includes a cylindrical housing (102) having a terminal compartment (110) and an electronics compartment (108) separated by a bulkhead (106). The terminal compartment (110) used for conductor connection is subject to moisture accumulation. An access channel (136) fully intersects an internal surface of terminal compartment (110) such that the access channel (136) drains moisture from the terminal compartment (110) across a range of mounting orientations. The transmitter (100) includes a circuit (104) in the electronics compartment (108) for compensating a process variable and providing the compensated process variable via a feedthrough circuit assembly (142) in the bulkhead (106), which in one embodiment, includes an encapsulated radio frequency interference filter (144), to terminals (132A, 132B) in the terminal compartment (110) for coupling to a conductor (134A, 134B) that is connected to an external controller.

Description

Have rhone and improve the transmitter that the RFI filtered method is installed

The disclosed part of this patent document comprises data protected by copyright.For appear at patent and trademark office patent filing or the record in by the patent document or patent disclosure of anyone facsimile copy, the copyright holder has no objection, but keeps the right of whole copyrights in all other cases.

The present invention relates to the transmitter that is used for industrial process control system.Particularly, the present invention relates to the process variable transmitter that is applicable under high humility or the wet environment operating condition.

The transmitters sense process variable has various uses, such as in oil gas refinery, and chemicals and tank station and chemical plant.Process variable (PV) is detected parameter or a detected product property in the process, it comprise absolute pressure, pressure reduction, temperature, flow, material height, or the like.A common application of transmitter is to utilize transmitter to go to detect a process variable of representing process, and by cable process variable is sent to controller.For a pair of wire transmitter, cable line is a twisted-pair cable cable group.Transmitter and controller are connected into a current return by cable.Transmitter does not have external power, and the running power that it obtains is from current return.Be typically, transmitter is regulated the function of the size of electric current in the current return as detected PV.In the agreement of a standard, the scope of electric current 4 to 20mA.Three-way and four wire transmitters use other cable line also to be fit to.

Transmitter is generally cylindrical box, and a dividing plate is divided into two compartments with casing, and each compartment has a threaded lid to bind.Used right cylinder is defined as by given curved surface and two solids that parallel surface is surrounded as in this patent description.The electronics compartment is equipped with the electronic circuit that detects with compensation PV, and the line end compartment is equipped with the PV that connection compensated and the Wiring port of cable.The circuit that feedthrough between two compartments is arranged on the dividing plate.The line end compartment comprises an external thread exit and entrance, and cable enters into the transmitter casing by this passage and links to each other with transmitter.Many transmitter casings have two threaded exit and entrances at the line end compartment, are used to connect outside hollow electric conduit.Hollow tubing conductor has formed the path between controller and the transmitter, and the inner cable of protection.The cable of two-wire transmitter typically has two leads.The position of exit and entrance is different with the difference of various transmitter casings, and its scope is that top from casing is to the bottom.For temperature transmitter, the top is meant transmitter casing that side relative with installation base.For the transmitter of pressure and other types, the top is meant transmitter casing that side relative with the process sensor position.

Though transmitter is used in the very poor commercial Application of various environment usually, when transmitter was installed in humidity or high humility running environment, variety of issue had still produced.Except the transmitter of hermetic seal, the gathering of moisture content is the common issue with that runs in the transmitter design in the line end compartment.The transmitter cost of hermetic seal is very high, and be difficult to assembling and repair, because hermetic seal welded seal normally.In the transmitter of non-hermetic seal, as irregular draining, the cohesion of moisture is full of casing sometimes in the casing.This moisture accumulation causes in the line end compartment electric short circuit between the terminals, crosstalk or the growth of organism or dendritic metal thing, and these situations all make the performance of transmitter reduce.Dendroid growth is metallic ion to be transferred to insulating surface and the filament that forms by liquid, and this filament is grown under the influence of Dc bias.If filament is connected across between the lead, just can generate the Low ESR drain circuit.The problem relevant with cohesion is that moisture content invades transmitter.If stood the directed steam such as high pressure washing or down-pour, blow-by or hermetic seal transmitter improperly will be assembled moisture content in inside.Harmful effect of assembling moisture content is the same with cohesion moisture content.In Fig. 1 of prior art, generally one line end compartment 52 is arranged with 50 transmitters of representing, from then on the moisture content that venting is assembled in the compartment is very difficult.The perforate 54 of a pair of exit and entrance is positioned at the top 56 of transmitter 50, and the feasible any moisture content that enters into exit and entrance 54 is all fallen the bottom of line end compartment 52 and is collected in the there.Even rotation transmitter 50 is also installed with 90 ° of orientations, line end compartment 52 is still partly filled with waterline 58, because exit and entrance not have the moisture content of venting gathering fully.Because the structure of the wall in the transmitter casing 60 is outstanding from the inside surface of compartment 52, even when transmitter 50 side direction are installed, moisture content must gather the height of waterline 58 and just discharge.

Moisture also can reduce the effect that radio frequency in the transmitter is interfered (RFI) wave filter or feeder line.In order to reduce the influence of processing environment electrical noise to greatest extent, shielding is in faraday cup usually for the PV electronic circuit, and this faraday cup is to be made of the RFI wave filter on electronics compartment, access cover and the electric signal joint in the transmitter.If any one of faraday cup is partially damaged, required insulation becomes invalid and has reduced the performance of transmitter.Typical R FI wave filter comprises that is with an externally threaded can, can be screwed into dividing plate to the RFI wave filter.When moisture was assembled between lead and RFI filter hut, moisture went wrong the RFI wave filter.Between RFI filter hut and lead, form a Low ESR drain circuit, so damaged the electrical insulating property of lead.Another problem of RFI wave filter is by keeping dividing plate waterproof and cause.The RFI wave filter is screwed into dividing plate, and makes lead be exposed to the both sides of dividing plate, produce one and seal problem.Yet, requiredly when threaded RFI wave filter is screwed into seal insertion force or moment unnecessarily makes the RFI wave filter bear stress.A RFI wave filter that meets with stresses can not provide required electrical insulating property, reduces the performance of transmitter sometimes, if test when assembling, will need to do over again in a large number in manufacture process.

So, just need a kind of transmitter that can impel venting ponding in the transmitter.Another required characteristics of transmitter are that reliable feed-through circuits is arranged, and this circuit can not given the element stress application in assembling process, just can be assembled into.

Transmitter by a detected process variable of lead transmission comprises a cylindrical box, and this casing has a line end compartment and an electronics compartment that is separated by dividing plate.The line end compartment that is used for the lead connection subjects to moisture content and gathers.The whole inside surface with the line end compartment of exit and entrance intersects, and makes that exit and entrance can be discharged moisture content from the line end compartment in certain device orientation range.Transmitter comprises the circuit in the electronics compartment, this circuit compensation process variable, and the process variable that makes this compensation is sent to the terminals of line end compartment by the feed-through circuits on the dividing plate, be used to be coupled to the lead that connects peripheral control unit, in a certain example, this feed-through circuits comprises the radio frequency interference filter of an encapsulation.

Fig. 1 is the view of former technology transmitter line end compartment;

Fig. 2 is the end-view of transmitter line end compartment of the present invention;

Fig. 3 is the part skeleton view that transmitter of the present invention decomposes;

Fig. 4 A and 4B are the cut-open views of upright and side direction installation of the present invention, and line end compartment internal drainage potentiality and cable interface are shown;

Fig. 4 C is the detailed view of transmitter among Fig. 4 B, illustrates to have another example that increases the draining potentiality;

Fig. 5 is the skeleton view of transmitter shown in Fig. 4 A; And

Fig. 6 is the cut-away section of transmitter of the present invention, and the feed-through circuits that is assembled into is shown.

In Fig. 2 and Fig. 3, transmitter 100 comprises casing 102.Casing 102 has two compartments that separated by dividing plate 106; An electronics compartment 108 and a line end compartment 110.Casing 102 has a top 112, bottom 114, threaded line end end face 116 and threaded electronics end face 118.The installation base district 126 that the bottom 114 of casing 102 has a machining to pack into and be suitable in the casing 102.Casing 102 is cylindrical, and columniform central shaft is by connecting circular electronics end face 118 central points and circular line end end face 116 central points.Line end compartment 110 is covered on line end end face 116 by lid 128 and constitutes.Electronics compartment 108 is covered on electronics end face 118 by lid 130 and constitutes.Line end compartment 110 share a dividing plate 106 that constitutes each compartment 108,110 rear portion with electronics compartment 108.On dividing plate 106 surfaces of line end compartment a revetment 120 is arranged; Revetment 120 is integrally attached to the inside surface of line end compartment 110.On dividing plate 106 surfaces in the electronics compartment 108 a feedthrough installation base 124 is arranged.Feed-through circuits perforate 141 is that break-through dividing plate 106 forms, and is convenient to the contact of electric signal between the compartment 108,110.Casing 102 the most handy pressure casting methods are made, and make installation base 126,124 and assembly district 108,110 reach required tolerance and smooth finish through machining then.Lid 128,130 preferably includes external thread group 129A, 131A and the internal thread group 129B at compartment 108,110 inner edges that matches with it, 131B.The special thread interface of lid 128,130 has stronger flame to stop path than other hickey.In the transmitter implode incident that may not take place, overvoltage forces screw thread 129A-B, and 131A-B intermeshes rather than separated by force.

In Fig. 4 A-B, line end compartment 110 comprises a Junction box assembly 132, is used for the cable 134 of couple of conductor 1345A-B is connected to the controller (not shown).Whole revetment 120 is divided into element installing zone 138 and gathering ground 140 with line end compartment 110.The wall that a pair of exit and entrance 136,137 passes line end compartment 110 in transmitter 100 bottoms 114 enters casing 102.When mounted, conduit 158 be by NPT joint 160 or similarly joint be screwed into a passage in the exit and entrance 136,137, and lead 134A-B links to each other with connection terminal 132A-B on the Junction box assembly 132 respectively.Zone below revetment 120 is gathering ground 140, and it comprises the internal openings and the cable duct tube 156 of exit and entrance 136,137.

In Fig. 3, electronics compartment 108 comprises suitably process variable (PV) electronic circuit 104 of design.Electronic circuit 104 receives the temperature signal that detects from the temperature sensor (not shown).The detected temperatures signal of 104 pairs of known reproducibility errors of electronic circuit is compensated, and output represents the current signal of this detected temperatures to terminal box 132.Electronic circuit 104 is connected on circuit by the combination of the feed-through circuits by dividing plate 106 142 with lead 134A-B on being connected in terminal box 132, and this feed-through circuits combination comprises eight RFI wave filters 144 and an installing plate 166.All electric signal that are connected to electronic circuit 104 are connected on the RFI wave filter 144 by signal lead.Electronics compartment 108 usefulness access covers 130 are protected from the outside.Feed-through circuits combination 142 and feed-through circuits perforate 141 usefulness sealants 154 are filled or encapsulation, make dividing

plate

106 and 110 sealings of electronics compartment.When using suitable electronic circuit 104, transmitter 100 can become provides the output of representing other testing process variablees, is gauge pressure, flow, pH value or other such as absolute temperature, the temperature difference, pressure differential, absolute pressure.

Fig. 4 A-B represents the installation configuration of a pair of standard, and transmitter 100 is installed on the carriage 162, and carriage is fixed on the installation base 126.Carriage 162 is fixed on pillar 164 or the similar stilt.In the direction of any installation, one of exit and entrance 136,137 links to each other with conduit 158, and plays draining.At the upright installation direction shown in Fig. 4 A, the function of exit and

entrance

136 or 137 drainages is identical.When after transmitter 100 is from vertical direction along clockwise (or inhour) direction deflection, installing, a lower passage draining in the exit and entrance 136,137.The two has pointed out minimum point 149 Fig. 4 A-B, and this point is transmitter 100 interior points from compartment 110 drainings moisture content arrival before.When transmitter 100 along various installation directions fixedly the time, minimum point 149 changes the position thereupon.

The discharge structure of compartment 110 comprises revetment 120, gathering ground 140 and exit and entrance 136,137.Whole inside surfaces of compartment 110 grind very smoothly, become a continuous casting plane, make moisture content focus on gathering ground 140.The inner all joint face of compartment 110 is for all equatings of same purpose.The zone that water droplet can adhere to has been limited in the smooth surface and the junction of equating, under the effect of gravity, impels the water droplet of formation to flow to gathering ground 140.

Exit and entrance 136,137 flushes with the inside surface of compartment 110 with the infall of line end compartment 110 inside surfaces.The sort of other structures of shown in Figure 1 60 in the compartment 110 inner as former technology, this structure has hindered moisture content and has discharged from passage 136,137.Preferably, downward-sloping from casing 102 extended passage 136,137 those parts, to strengthen drainability.In Fig. 4 A, transmitter 100 (promptly from stand up position to 60 ° of either direction deflections) in 120 ° of fitting limits can be discharged moisture content fully, as the pointed scope of dotted line 147.In same figure, when turning over whole 180 ° when installing, transmitter 100 allows small amount of moisture to be assembled in compartment 110, but is not enough to touch electronic circuit or terminals.

Shown in Fig. 4 C is a preferred embodiment of the present invention, and this figure has amplified near exit and entrance 136,137 zone with compartment 110 infalls among Fig. 4 B.Particularly, 145 zones of pointing out in Fig. 4 C, each angle are all evened up and are increased aperture area, and the final shiny surface that forms can turn on whole 180 ° of installation directions (promptly from stand up position to 90 ° of either direction deflections) draining.The top enlarging of exit and entrance 136,137 and compartment 110 inwall internal chiasmas place makes the height of waterline 143 (as shown in Fig. 4 B) be reduced to the height of waterline 151.Terminal box 132 and lead 132A-G are higher than waterline 151 forever, so the moisture content that can not be assembled is got wet.All circuit are connected and all are placed on the exit and entrance 136,137 between terminal box 132 and the lead 134A-B, and holding circuit connects dry.Enlarging district 136A and 137A (not shown) are in when casting or after this form during machining, but be not by the interpolation material to casing 102, but in existing wall construction, form.Enlarging district 136A, 137A can be the narrow passages that forms on compartment 110 inwalls, and this narrow passage is to extend to minimum point 149 from exit and entrance 136,137, or widen unwatering system shown in Fig. 4 C.In all cases, enlarging district 136A, the inside surface of 137A and gathering ground 140 blendes together one, is beneficial to venting moisture content to reduce sharp edges.

Cable duct tube 156 is the two lead 134A-B deflection Junction box assemblies 132 of turning round that insert.The changed course of cable distribution 134 distributes lead 134A-B easily and has avoided the lead winding.Exit and entrance 136,137 preferably is positioned at relative both sides on line end compartment 110 bottoms, makes a cable duct tube 156 be used for the cable distribution of two passages 136,137.Cable duct tube 156 is castings or is installed on the inside surface of the compartment 110 between exit and

entrance

136 and 137, and is inclined to moisture content and can flows out to exit and entrance 136,137 from cable duct tube 156.After opening, lead 134A-B is connected respectively to terminal box 132.Lead 134A-B has equal length usually, almost equal the longest adapter path of terminal box 132, so every lead all has unnecessary length, terminal box cover 131 is to make with non-conductive plastics, and have the water chestnut curved shape, can make lead center on central distribution.The unnecessary length of lead 134A-B leaves in the compartment 110.Remove unessential structure in the gathering ground 140, the shape of Junction box assembly 132 can make the unnecessary length that has more space to deposit lead in the compartment 110, the short circuit of closing and having avoided clamping wire to cause when covering.

In Fig. 3 and Fig. 6, interface card 152 is fixed on element installing zone 138 in the compartment 108, and plastic jacket 131 is topped on circuit board 152 then, and screw terminal 132 stretches out outside the plastic jacket 131.Plastic jacket 131 makes each terminals insulation and they is separated, and has also protected the electronic component on the interface card 152 simultaneously.The shell of each wave filter all is welded to conductive mounting plate 166 in eight RFI wave filters 144, thereby forms a complete feed-through circuits device 142.Device 142 inserts the perforate 141 of dividing plate 106, and is fixed on the metal screw on the boss 124 of integral installation.Installing plate 166 is also located RFI wave filter 144 so that encapsulation.Be grounding to casing 102 on the shell circuit of the key screw wave filter 144 of permanent circuit device 142 to the dividing plate 106.Interface card 152 provides mechanical pilot hole for screw terminal 132, and on circuit the signal lead of wave filter 144 is connected to screw terminal, and the some of them signal lead is represented the process variable that compensated.The sealant 154 of line end compartment 110 1 sides of dividing plate 106 is incorporated into around the circuit arrangement 142, so that complete closed between a compartment and another compartment.Sealant 154 is the epoxy packages compound preferably, but also can make with any curable potting compound.Be full of abundant sealant 154 in the element installing zone 138, make it to be raised to the height of revetment 120.In case populated sealant does not just have groove or hole in the element installing zone 138, just do not have the place can assemble moisture content yet and cause electric leakage.Any moisture content that may generate in installing zone 138 can be forced to flow to gathering ground 140 under the effect of gravity, and discharges from exit and entrance 136,137.Except sealant can strengthen the draining characteristics, sealant 154 makes between the shell of RFI wave filter and the signal lead and has in fact formed infinite impedance, thus limited basically signal and electrical ground between leakage current.Strengthening between the compartment between the environment insulation and signal and ground in the electrical isolation, the present invention has for good and all installed RFI wave filter 144 and has not had potential destrabilizing moment effect.In case sealant 154 solidifies, the signal lead of wave filter 144 just is connected to the signal contact on the electronic circuit 104 on the line end compartment.

RFI wave filter 144 is normally by π on the circuit, and L or C mode filter are formed to suppress high frequency noise.The configuration of commercial RFI wave filter 144 generally includes the ceramic capacitor of a hollow-cylindrical.Conductive material on cylinder medial surface and lateral surface constitutes this capacitor.The external surface grounded shell that arrives of cylinder.Be connected to a lead (being signal lead) on the inside surface circuit of cylinder, this lead is exactly the length of wave filter.Other forms of RFI wave filter 144 may comprise the electrical noise filtering circuit of the combination of an inductor and capacitor, current splitter, series inductance impedance or other types.

The invention provides a kind of transmitter design that is directed at electric fault because of catchmenting that resists, it can discharge ponding in the installation direction of wide range.Transmitter of the present invention can not need additional external hardware or special conduit draining at very wide installation site scope internal drainage.Bottom 114 places exit and entrance 136,137 staggered relatively also makes the cable conductor orientation enter transmitter 100, is convenient to being connected of lead and terminals.Sealant 154 provides electrical isolation and the environment insulation that has improved, and for good and all makes RFI wave filter 144 location, and has avoided the distorting stress in the installation process.In addition, with sealant element installing zone 138 is filled into and revetment 120 corresponding to height, this has guaranteed that guiding moisture content is to the gathering ground 140 and finally discharge from exit and entrance.

The inventive method disclosed herein and content are described with reference to a preferred embodiment.The worker who knows this technology recognizes, can do some change in form and details not departing under the spirit and scope condition of this invention.

Claims

1. Transmitters that transmit process variables via cables include:

A cylindrical tank with a process device, the process device is placed on the base of the tank, the tank has a first compartment and a second compartment, sharing a partition, the second compartment helps to absorb moisture, so covered with a lid;

A first access channel arranged on the box, adjacent to the process device in the second compartment, the intersection formed by the access channel is substantially flush with the inner surface of the second compartment, and the access channel can be connected to the electrical equipment containing the cable Catheter outer section;

a circuit for compensating the process variable in the first compartment, the circuit providing the compensated process variable to a feedthrough circuit in the bulkhead; and

A pair of terminals connecting the feedthrough circuit and a pair of wires in the cable in the second compartment, the transmitter drains moisture from the second compartment through channels within the confines of the device.

2. The transmitter of claim 1, wherein the first compartment includes a passageway connected to a sensor that senses the process variable, the passageway and the sensor being disposed within the housing of the transmitter.

3. The transmitter according to claim 1, wherein a whole piece of wall is arranged on the surface of the partition in the second compartment, in order to divide the partition into a component mounting area and a water collection area; the component mounting area is used for fixing wiring end, while the catchment area collects water into the entry and exit channels.

4. The transmitter of claim 3, wherein the access channel is fully integrated with the inner surface of the second compartment in the catchment area such that when the transmitter is installed with the access channel downwardly oriented, the access channel substantially collects total moisture in the catchment area.

5. The transmitter of claim 3, wherein the bulkhead has an opening, and the transmitter further comprises:

At least one RFI filter is arranged on the upper mounting plate; and

Sealant that fills the component mounting area up to the top of the entire wall.

6. The transmitter of claim 3, wherein the pair of connecting surfaces in the second compartment are rounded.

7. The transmitter of claim 3, wherein the water collection area has a smooth surface to facilitate drainage of water.

8. The transmitter of claim 1, wherein the second access passage entirely intersects the interior surface of the second compartment, the second access passage being substantially opposite the first access passage.

9. The transmitter according to claim 8, wherein an integral wall is arranged on the surface of the partition in the second compartment, in order to divide the partition into a component mounting area and a water collection area; the component mounting area is used for fixing wiring end, while the catchment area collects water into one of the entry and exit channels.

10. The transmitter box includes:

The internal partition that divides the box into the line end compartment and the electronic compartment has an opening on the partition and a retaining wall in the line end compartment. The retaining wall divides the divider into the component installation area and the water collection area;

A mounting plate for fixing a group of radio frequency interference (RFI) filters, each RFI filter has a shell and a wire arranged along the length of the filter, the mounting plate is connected to each RFI filter shell, and the mounting plate is fixed on in openings in partitions; and

Filler element installation area substantially reaches the sealant at the top of the parapet in order to seal the compartments from each other.

11. The method for assembling the transmitter box, including:

arranging an RFI filter on the mounting board, the filter having a housing and a conductor running along the length of the filter, the filter housing being connected to the mounting board;

Fix the mounting plate on the opening of the partition in the box. The partition divides the transmitter into two compartments. There is a protective wall on the partition to divide one of the compartments into the component installation area and the water collection area. ; one end of the wire on the mounting board is in one compartment and the other end of the wire is in the other compartment; and filling the component mounting area with a sealant in order to hermetically separate one compartment from the other.

12. The method of claim 11, wherein the sealant substantially prevents migration of moisture from one compartment to the other compartment.

13. Transmitters that transmit process variables through wires include:

A tank with a process device, the process device is placed at the bottom of the tank, the tank has a first compartment and a second compartment, sharing an inner partition, the second compartment helps to receive moisture, the compartment an opening in the plate and a retaining wall;

An access channel disposed on the housing adjacent to the process device and having an opening into the second compartment, the access channel forming an intersection substantially flush with the inner surface of the second compartment, the access channel capable of being connected to the the outer section of the electrical conduit;

within the first compartment are electronic circuits providing a signal indicative of the compensated process variable;

a feedthrough circuit arranged over the aperture, the circuit comprising an RFI filter having a housing and a signal lead disposed along the length of the filter, one end of the lead being in the first compartment and connected to the signal;

a sealant that substantially fills the element area to the top of the parapet; and

The second compartment connects the other end of the wire to the terminal of the signal lead, and the transmitter drains moisture through the channel within the confines of the device.