Flow Meter Pitot Tube With Temperature Sensor

The present invention relates to pitot tube type flow meters for use in confined conduits, such as pipes, and more particularly to a combined apparatus for sensing the relevant pressures and the temperature of the flowing fluid and conveying signals representative thereof to a transmitter which develops and transmits electrical signals representative of the fluid flow variables, such as rate, volume and mass.

Pitot tube flow sensors of the type disclosed in U.S. Pat. No. 4,559,836 to Darrel F. Coleman et al. have been in use for many years in differential pressure flow measurement systems to detect the average impact, or high pressure, on the upstream facing side of the pitot tube and to detect low fluid pressure on the downstream facing side of the tube. Traditionally, the high and low fluid pressures have been used to derive an electrical signal representative of fluid flow rate.

The fluid pressures sensed and conveyed by the pitot tube or other kind of differential pressure sensor, such as an orifice plate, for example, are conveyed to a pressure transducer through an interconnecting head, such as the one shown by reference numeral 24 in the said '836 U.S. Patent, or by a valve manifold, such as the one shown by reference numeral 17 in U.S. Pat. No. 4,466,290 to Roger L. Frick.

When it is desired to sense the temperature of the medium flowing in the pipe, temperature sensing devices such as a Thermowell RTD (Resistive Temperature Device) have been used, inserting the RTD into a protective sheath, such as a "Thermowell", which is immersed in the fluid whose temperature is being sensed.

In the continued development of sophisticated flow measurement systems for processing fluids it has become increasingly important to be able to measure volume and mass of fluid, as well as rate. In order to do that, however, temperature of the fluid must be known. Because intrusive measurement of the various parameters of a fluid flowing in a pipe requires penetration of the pipe, it is also important to sense the required parameters with a single instrument, requiring only one intrusion into the pipe.

It is therefore, the primary object of the present invention to provide a single apparatus for sensing temperature in a fluid flowing in a confined channel, as well as sensing the high and low pressures which have been previously detected by a pitot tube type of flow sensor.

A second object of the invention is to provide a combination temperature and pressure sensing device for fluid flowing in a pipe that will allow the temperature sensing portion of the assembly to be removed and replaced without having to also remove the primary pressure sensor from the pipe.

Another object of the present invention is to advantageously use the available space inside of a prior art pitot tube to house a temperature sensing device.

Other and further objects, features and advantages of the invention will become apparent upon a reading of the detailed description of a preferred form of the present invention.

FIG. 1 is perspective view of a fluid flow measurement system in which the elements of the present invention function.

FIG. 2 is an enlarged cross sectional view taken along line 2--2 of FIG. 1.

FIG. 3 is a cross sectional view of the primary flow sensor of the present invention, including the pipe into which the combined pressure and temperature sensor elements are inserted and the manifold head mounted on the proximal end of the sensor.

FIG. 4 is an end view of the manifold of the present invention showing the riser and the terminal housing on one side of the manifold and the receptacle for one of the pressure valves on the end shown. The opposite end is a mirror image of the end shown.

FIG. 5 is a cross sectional view taken along lines 5--5 of FIG. 4.

FIG. 6 is a side view of the preferred form of temperature sensor.

FIG. 1 illustrates a typical flow measurement system 2 to which the combination of the present invention is applied. The primary portion of the system comprises a pitot tube type of differential pressure flow sensor 4 (of the type described in the above referred to U.S. Pat. No. 4,559,836), which is inserted diametrically into a pipe 6 carrying fluid. The mounting hardware, which forms no part of the present invention, is shown generally by reference numeral 8. The proximal end of the pitot tube terminates in a manifold head 10 where the high and low pressure fluids are conveyed though interior channels of the manifold to a pressure transducer 12 mounted directly to the manifold 10. As shown in FIG. 5, the interior fluid conducting conduits 11 and 13 in the manifold pass respectively through a pair of shut off valves which are disposed in threaded receptacles 14 and 16 of the manifold. One valve 18, of the two, is shown in FIG. 1. A third, equalizing valve 20, positioned in receptacle 22 in the manifold, is opened to interconnect the high and low pressure conduits 11 and 13 to equalize the fluid pressure in the manifold for the purpose of calibrating the transmitter. While a three valve manifold is shown, a five valve to manifold can be employed with the present invention.

Attached to the pressure transducer 12 is the so-called differential pressure transmitter 24, but which, in the context of this invention, processes and transmits signals representative of the mass and volume of the fluid flowing in the pipe 6, as well as differential pressure and fluid flow rate.

Attached to one face of the manifold 10 is a riser 26 which supports a housing 28, containing an electrical terminal (not shown). The terminal inside the housing 28 interconnects the wiring 30 from a temperature sensing device with other wiring (not shown) which conducts the temperature signal into the differential pressure transmitter 24 for use in determining the mass and/or volume of the fluid in the pipe 6.

The temperature sensing device 32 is preferably a resistive temperature device such as the ARI and Weed RTD manufactured by Texas Thermowell, Inc. Such a device comprises an elongated rigid resistive element 34 having conductors 30 which convey the signal from the resistive element to a further signal processing site. Referring now to FIGS. 1 and 2, the RTD temperature sensor is seen in its installed position within a space in the pitot tube 4 between the high and low pressure plenums 40 and 42.

As seen in FIG. 3, the manifold 10, in addition to the valves and conduits already mentioned, contains a bore 35 which traverses through the body of the manifold. The bore 35 is sized and positioned in the manifold to act as a conduit through which the rigid resistive element 34 of the RTD temperature sensor 32 is passed during its insertion into, or retraction from, the pitot tube 4. When the rigid to portion 34 of the temperature sensor is fully inserted into the pitot tube, the temperature sensor conductors 30 are then trained through a transverse duct 42 in the manifold 10, which duct is in communication with the riser 26. The conductors are run through the riser to be connected to the terminal in the housing 28.

One end of the bore 35 is provided with two radially enlarged and threaded receptacles 36 and 38, of different diameters. After the temperature sensor 32 is in position in the pitot tube and the manifold, a threaded collar 41 on the proximal end of the elongated resistive portion 34 of the temperature sensor is threaded into the small receptacle 38 for the purpose of mounting and securing the temperature sensor. After the temperature sensor is thus secured, a threaded sealing plug 43 is screwed into the larger outer receptacle 36 after which the pressure transducer 12 can be attached to the manifold, as it is shown to be in FIG. 1.