FIELD OF THE INVENTION
The present invention generally relates to Radar application for Level measurement in blast furnace, in particular a top mounted surface level sensing device in microwave Radar application. More particularly, the invention relates to a device for protection of antenna of the radar system to reduce radar malfunctions in harsh condition applications for example, a blast furnace.
BACKGROUND OF THE INVENTION
A Radar Level transmitter is used to measure level of any process tank. After calibrating the bottom distance of the process tank, the radar transmitter senses the transmitted echoes from the bottom of the tank, and the distance from the top of the tank finally provides the prediction level. The Radar uses Doppler Effect with Frequency Modulated Continuous Wave (FMCW) in determining the distance of surface/level to be measured. The radar source is usually a trans-receiver:

transmitting and receiving Electromagnetic signals with a single antenna. The antenna can either be a Rod type or a Horn (Cone) type or a Parabolic type or a hybrid of the three types.
According to the prior art, the antenna is embedded in the ceiling of the process tank being directly exposed for surface of measurement. Radar electronics are usually connected to the antenna via a flange separating the antenna from the process. Radar waveguide source is head mounted over the antenna and is not exposed directly to the process conditions. The Antenna and Electronics are usually separated by a waveguide with a PTFE or Quartz sealing. Additional arrangements for cooling the electronics and purging arrangement for the antenna are also known.
The Prior art antenna systems have many limitation for example, malfunctioning of the radar due to failure of the antenna, the cause of failure being operation under harsh process conditions. The antenna failures may be categorized as:
a. damaging of Parabolic antenna.
b. choking of Horn (Cone) antenna
c. damaging of exposed rod antenna

Further, radar malfunctioning might cause due to susceptibility of high ambient temperatures by the radar being located proximal to the harsh process condItions. It is known that online maintenance of the antenna is not feasible due to risk of direct exposures of the operators to harmful process conditions thereby demanding a process shut down resulting in production losses in most of the applications. (Especially in case of Blast furnace radar type stock level application).
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device for protection of antenna of the radar system to reduce radar malfunctions in harsh condition applications of the system, which eliminates prior art problems.
Another object of the invention is to propose a device for protection of antenna of the radar system to reduce radar malfunctions in harsh condition applications of the system, which allows easy maintenance of the antenna by avoiding exposure of operators to harmful process environment which interalia in-turn reduces the process quality vis-a-vis production loss,

A further object of the invention is to propose a device for protection of radar system to reduce radar malfunctions in harsh condition applications of the system, which includes cooling means for the radar electronics as well as the waveguide to protect the radar from harsh environmental conditions.
SUMMARY OF THE INVENTION
According to the invention, there is provided a device for protection of antenna of the radar system to reduce radar malfunctions in harsh condition applications of the system. The device comprises:
- an insulated cooling cabinet mounted over the Radar Flange to protect the electronics;
- a spool piece for protuberant orientation of the Radar antenna with purging means for safe operation; and
- a Ball Valve located at a measured distance for isolation of the radar from the harsh conditions of the process inside a blast furnace.
Insulated cabinet is designed from metal sheets with a chamber for insulation in between two sheets per face for six faces. The cabinet is designed for bottom

entry of the radar electronics with an easy mounting arrangement. This ensures adequate Mechanical and Thermal protection. The heat generated by the Radar electronics and the Waveguide source operation is purged with help of compressed Nitrogen entry into the cabinet.
A protuberant Spool Piece holding holds the antenna including its flange. The spool dimensions is derived from the antenna specification and calculated from the angle of divergence expected from the radar source. The protuberant design of the spool above the tank surface reduces harm from direct exposures to harsh process conditions.
A Valve and flange assembly is disposed to isolate the radar system from the furnace. This provides process isolation against fumes and gasses, and sealing them during antenna cleaning/replacement This arrangement can be automated with pneumatics control to close during the unsafe conditions in order to protect the antenna and waveguide.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 shows schematically a prior art and the inventive device for Blast furnace stock level measurement
Figure 2 shows the transmitter cabinet mounting according to the invention.
Figure 3 pictorially explains the inventive device for (a) Rod Type Antenna (b) Parabolic Type Antenna.
Figure 4 an echo propagation in Prior art for both healthy and choked/malfunctioned antenna with a comparative view of echo propagation in the invented device.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Figure 1, the inventive device comprises:
a) an electronics cooling cabinet; and
b) a spool and valve assembly;
a)
Electronics cooling cabinet
An insulted electronics Cabinet (ECC) is fabricated out of thin metal sheet (2.1) as shown in Figure 2. This sheet (2.1) is also Powder-coated with epoxy paint to provide antirust finishing. The cabinet can be opened from front and back face (2.8) by opening the bolts. The front and rear cover (2.8) both is insulated with Glass wool packing (2.3) in between two plates each. The Bottom face has a Radar flange (2.G) interposed between two insulated sheets with holes cutout and provided with three support located at 1200 angle for bolting with the bolts of the flange (2.8).
The side walls and ceiling is cast with a single run of two sheets with the Glass wool insulation packing (2.3) in between. An entry point (2.2) is provided through the sidewalls for purge nitrogen inlet and a filtered exit (2.4) is provided at other sidewall. This entry (2.2) provides a suitable flow for the cooling of electronics even at 5 Bar pressure of source. The Glass wool (2.3) prevents heat transfer by conduction as the radar is often mounted in a high temperature zone.

The Radar electronics has a minimum working space from the walls. Cabinet size can be derived as a Square with length

Spool and Valve assembly
As the Radar Operates at microwave frequencies, irrespective of the antenna design, all the manufactures select different angle of operation and distance measurement for the radar. The spool and valve assembly is used to keep the echoes undisturbed [Fig4 shows the disturbed echoes]. The distance of the Ball valve is kept as minimum as possible from the antenna. Inner diameter of both the spool and Ball valve being an important parameter, is kept in consideration while designing the assembly. The Spool piece has one purge entry and one exit for purging the spool and valve assembly after the isolation valve is closed. The orientation of the spool piece is kept outside the furnace so as to reduce exposure and damages by the process conditions.

The Blast furnace stock level radar operates on about 10 GHz frequency. The microwave thus generated has a specific sourcing angle eDi~pet*on with Vertical. Now the waves propagate through this sourcing angle, must be free of any interruption by any component if introduced during, design modification. This is achieved by putting the Ball valve close to the antenna wherein the distance of the valve is selected by the relationship of:

Where eDi~person usually lies between 6°-8° angles from vertical.

having Ball valve Immediately after antenna ends. Hence, the ratio is to be maintained asowed comes as
4.77Mtrs and the complete device is designed under 3 Mtrs of length, according to one embodiment of the invention.
On detection of any signal of the Radar representing malfunction, the Ball valve is closed after bypassing its process interlocks. The Purge arrangements in the spool piece are kept open for allowing the gasses to get cleaned. The radar is opened

from the waveguide flange and jamming if found is cleaned. No gasses come out from process due to Isolation through the Ball valve. After a visual inspection, if the antenna is found damaged the same can be replaced by lifting the spool and radar after the furnace is isolated through the ball valve.
Advantages of the invention
1. Choking of Horn (cone) antenna and damages to other types of antenna is substantially reduced.
2. Easy maintenance of the antenna including antenna replacement without taking shutdown of the process.
3. Enhanced life of the antenna waveguide due to isolation of the radar and antenna.
4. Electronics malfunction is considerably reduced because of
a. increased distance maintained between the process location and the
protuberant radar flange.
b. provision of an insulated cabinet.

WE CLAIM
1. A device for protection of an antenna of blast furnace stock level radar systems to reduce malfunctioning frequency of the radar system operating under harsh conditions, the device comprising:
- an insulated cooling cabinet mounted over a radar flange to protect the radar electronics;
- a spool piece for protuberant orientation of the radar antenna provided with means for purging inert gases; and
- a ball valve assembly disposed at a predetermined distance for isolation of the radar from the harsh process conditions inside the blastfurnace,
wherein the predetermined distant (LAllowed) of the ball valve (BV) is selected based on the radius of the ball valve (Rav) sourcing angle of the microwave (SDiSpereionn generated by the radar in respect of vertical, length of the antenna (Lantenna), and internal diameter of the flange (Flange ID), wherein the distance allowed (LAllowed) = Rav X
COT(eDisperW2), wherein RBV = {(Untenaa + iQ^lo) X TAN
(SDiSperaon/2)}, and wherein the SDispersion is between 60 to 8° from the vertical.

2. The device as claimed in claim 1, wherein a ratio of Rav : LAllowed ? 0.0524.
3. The device as claimed in claim 1, wherein the insulated cooling cabinet is made of metal sheets coated with epoxy paint, wherein the front and rear cover is insulated with glass wool, and wherein the radar flange is interposed at the bottom of the cabinet.
4. The device as claimed in claim 1, wherein one each entry point and exhaust point is configured on the side walls of the cabinet.
5. The device as claimed in claim 1, wherein the length of the cabinet (L) is equal to summation of flange 1D (