Abstract:
The present invention is a consistency transmitter for the measurement of consistency, viscosity, and other properties of matter. The transmitter consists of a measuring element, attached to a bearing-mounted shaft and rotated in the matter to be measured by a direct drive motor that is positioned coaxially with the measuring element and its shaft. The stator of the direct drive motor is integrated into the consistency transmitter body, its rotor into the shaft. The stator is coaxially attached to a first flange that transmits the torsional force of the motor with flexible elements to a second flange positioned on the shaft. The first and second flanges are attached to differential elements with which the phase angle between the flanges is measured using measuring elements located near the flanges. The shaft of the measuring element is bearing-mounted inside a tubular torsion shaft. The consistency transmitter can be inserted into an operating process by means of special installation equipment consisting of a shut-off valve combined with an insertion pipe. The insertion pipe includes regulating elements in such a way that they match with the matching elements on the transmitter body. With the help of regulating elements and matching elements, the transmitter can be inserted to the desired depth in the process.

Description:
BACKGROUND OF THE INVENTION 
   The object of the present invention is a consistency transmitter for the measurement of consistency, viscosity, and other such characteristics of matter. The object of the invention is particularly the consistency analyzers used in the pulp and paper industry. 
   In rotary consistency transmitters known in the prior art, a measuring element is rotated in the process being measured. Fibers and filler particles present in the measured matter, such as papermaking pulp, tend to resist the rotary motion of the measuring element. This resisting force, which is proportional to the shear force generated by the process matter, is measured using various torque measurement techniques and further converted into a variable indicating consistency. In prior art solutions the measuring element is rotated by a single-phase or three-phase motor that is located to the side of the rotation axis. The motor is connected to the torsion shaft by gear, chain, or belt drive transmission or some other power transmission system. Gearing is required in order to reduce the rotation speed. The use of single-phase or three-phase motor to rotate the measuring element poses several problems and limitations. 
   A three-phase motor suited for process conditions weighs from 6 to 10 kg, a single-phase motor over 10 kg. The motor has to be installed to the side of the torsion shaft, and thus the shaft forms a lever arm and the heavy motor causes a strong flexural and torsional stress at the point of the attachment to the process pipeline. Especially in process pipeworks, support structures must be installed, and these increase the investment cost. The bending and torsion caused by the weight of the motor also puts a strain on the torsion shaft. The weight of the motor and the required massiveness of the transmitter structure results in that the entire device may weigh over 30 kg. Thus, handling of the device requires several people or a hoist. 
   Power transmission elements require regular service and thus cause maintenance costs. For example, a transmission belt must be inspected for wear every six months and replaced every few years. The transmission belt causes extra bending strain on the torsion shaft and will thus contribute to more rapid wear of bearings and mechanical seals. 
   The rotation speed of single-phase and three-phase motors is dependent on the mains network frequency. The torque resisting the rotation of the measuring element increases exponentially as a function of both consistency and rotation speed of the measuring element. When the measuring element is rotated at a constant speed, its shape must be selected in accordance with the properties of the measured medium. The defining of suitable measuring elements causes additional costs and also increases the number of necessary spare parts. 
   Motor load, and thus also rotation speed, varies due to a number of reasons. Changes in rotation speed cause the measurement signal to drift and thereby complicate the measurement. Rotation speed changes when consistency, i.e. the shear force resisting measuring element rotation, changes. The rotation speed changes also due to changes in the friction of the torsion shaft bearings and mechanical seals. The friction forces in mechanical seals are affected by process pressure: a higher pressure forces the sealing surfaces more tightly against each other and thus increases friction. In cage induction motors, the backward slip that affects rotation speed is also dependent on motor load. 
   Most cage induction motors have a fixed direction of rotation, and as consequence, unwanted materials caught to the measuring element can only be removed if the device is first pulled out of the process. 
   Single-phase and three-phase motors require high-voltage operating power and must be well enclosed to protect them from moisture and the process environment. High voltage increases electrical safety requirements, and a qualified electrician is needed to install a three-phase motor to the power network or to disconnect it. Several single-phase and three-phase operating voltages are known in the world, and thus a separate motor type has to be chosen for each voltage. The need to provide for different operating voltages increases the variety of models and spare parts that a manufacturer has to offer. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a consistency transmitter where the measuring element is rotated by a direct drive motor. The rotor of the direct drive motor is coaxially attached to the torsion shaft of the measuring element, while its stator is attached to the support structure of the torsion shaft in such a way that the rotor and stator are coaxial. The direct drive motor is driven by control electronics in such a way that its rotation speed can be changed with a program. The torque caused by the process matter is transmitted along the shaft to a differential element, which consists of two coaxial flanges between which a phase shift resisted by spring elements is generated. Spring elements are attached in pairs to the flanges so that the phase shift is resisted by several pairs of spring elements. Each spring element pair is balanced so as to ensure that the phase shift will be directly proportional to the torque effective over the measuring element and measurable by using opto-electronic or electromagnetic device. 
   The condition of the bearings, seals, and other elements of the consistency transmitter can be monitored by observing the power consumption of the direct drive motor. The input power of the motor is consumed by the friction of the device&#39;s mechanical parts such as bearings and seals of the torsion shaft and by the rotation of the measuring element. The input power of the measuring element can be calculated from its torque, and when this input power is reduced from the total output, the result gives the power required to rotate the torsion shaft. The calculated input power of the torsion shaft will increase for example when bearings are worn or defective, and if this value exceeds a preset limit, the operator can be alerted. 
   The consistency transmitter can be installed into an operating process, and its insertion distance is adjustable. The drive shaft and the torsion shaft inside it are sealed in such a way that process medium cannot get in touch with the seal ring between the shafts. This sealing arrangement eliminates the effects of process medium on the seals and their friction. 
   A direct drive motor weighs less than 1 kg and thus causes an essentially smaller flexural strain than the motors according to the prior art. The entire consistency transmitter is a lightweight device that is easy to handle and install, even by a person working alone. 
   A direct drive motor does not include separate power transmission elements, e.g. belt or belt pulleys, to rotate the measuring element. The load on the bearings is substantially smaller, as the forces caused by power transmission are clearly lower. A direct drive motor can be integrated into the consistency transmitter, and its rotating parts can be balanced with regard to the rotating shaft. 
   The speed of a direct drive motor can be set to a desired level with a program. Constant feedback of motor rotation speed is obtained, and control electronics keep the rotation speed constant. With one variable stabilized, a more accurate measurement signal is obtained. For optimal consistency measurement it is advantageous, if the speed of the measuring element can be selected so that the desirable speed can be used in each measurement application. For example at high consistencies the rotating speed can be reduced, so as to expand the consistency measuring range of a measuring element. Freely selectable rotating speed means that only one measuring element is needed in order to measure consistency throughout the consistency range used in the pulp and paper industry, typically from 0.5% through 16%. 
   Unwanted materials (e.g. plastic shreds) may be present in the process and when these get caught to the measuring element, they cause errors in the measurement reading. By reversing the rotation direction, materials caught to the measuring element can be loosened without uninstalling the entire transmitter from the process. Moreover, the verification of the measuring element&#39;s zero point or automatic zero point calibration can be done by rotating the measuring element back and forth. If the measuring element is symmetrical, its zero point is the average of the torque readings measured when it is rotated back and forth; if it is asymmetrical, the zero point is between these torque readings. The zero point is specific for each measuring element and can be determined by means of laboratory tests. In some applications calibration can be carried out during operation by placing a calibration brake on the end of the rotation axis of the measuring element. 
   A direct drive motor&#39;s operating voltage is low, e.g. 48 V, which is advantageous as for its electrical safety. The cabling costs of a low-voltage power supply are considerably lower. Moreover, the electrotechnical components of a direct drive motor can be assembled in the same housing as the measurement electronics of the device, which reduces the investment and maintenance costs. 
   The present invention solves the problems listed above and corrects shortcomings of the prior art. It brings about a direct-drive powered consistency transmitter that is lightweight, easily controlled by program, has a low operating voltage, and is economical in total costs. 
   The above-mentioned advantages will be achieved by using a consistency transmitter according to the invention characterized by the features described in the independent claims. 
   The object of the invention is a consistency transmitter for the measurement of consistency, viscosity, and other characteristics of matter. The transmitter consists of a measuring element attached to a bearing-mounted shaft, which measuring element is rotated in the matter being measured. The measuring element is rotated by a direct drive motor that is positioned coaxially with the measuring element and its shaft. The stator of the direct drive motor is integrated into the body of the consistency transmitter, its rotor into the shaft. The rotor is connected to a first flange positioned coaxially with it, by which flange the torsional force of the motor is guided to the second flange on the shaft. The elements between the flanges function as torsional force transmission elements. Differential elements in connection with the first and second flanges indicate the phase angle between them. Close to the flanges there are means for measuring the phase angle between the flanges. The shaft of the measuring element is bearing-mounted inside a tubular torsion shaft. The drive shaft in turn is bearing-mounted inside the transmitter body and sealed at its front end to prevent the entry of process medium inside the device. The drive shaft is sealed in such a way that it can be lubricated and cooled with either water the pressure of which is higher than process pressure or with low-pressure circulating water. In connection with the torsion shaft are also means for sealing, which prevent the entry of process medium inside the transmitter. The task of the torsion shaft is to move the differential elements and their measuring elements further away from the process of variable temperatures. The coupling between torsion shaft and differential elements mechanically protects the differential elements against shocks and overload situations. In addition, the torsion shaft serves to eliminate from the measurement the torque losses caused by the friction of bearings and sealings. The measuring shaft has a small diameter in order to reduce its torque loss. The body of the consistency transmitter is elongated in shape so as to ensure that the measuring element can be inserted sufficiently far into the process. The consistency transmitter can be inserted into an operating process by using dedicated installation equipment. The installation equipment consists of a shut-off valve combined with an insertion pipe. The insertion pipe contains regulating elements that correspond with matching elements on the transmitter body. With the help of the regulating and matching elements, the transmitter can be inserted into the required depth in the process. The insertion distance of the transmitter can be changed while the process is operating, and it can be secured in position by using suitable locking elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the present invention will be described in more detail by some advantageous embodiments and with reference to the attached drawings. 
       FIG. 1  shows a consistency transmitter according to the invention, in side view and in cross section; 
       FIG. 2  shows a cross section of the measuring head of the device illustrated in  FIG. 1 ; 
       FIG. 3  shows a cross section of the drive end of the device illustrated in  FIG. 1 ; 
       FIG. 4  shows one possible method with which a device according to the invention can be inserted into a process; and 
       FIG. 5  shows the differential elements and calibration equipment of one application of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-5  illustrate a consistency transmitter according to the invention, which consists of measuring element  1 : torsion shaft  2 ; bearing and sealing element  3 ; differential elements  4 ; drive shaft  5 ; clamping element  6 ; clamping and sealing elements  7 ; rotor  8 ; stator  9 ; stator base  10 ; drive shaft body  11 ; end piece of drive shaft body  12 ; sealing elements  13 ; flange  14 ; sealing elements  15  and  19 ; bearing elements  16 ,  17  and  18 ; coupling element  20 , insertion pipe  21 ; valve  22 ; sealing elements  23  and clamping elements  24  and  25 ; control electronics  26 ; and calibration equipment  27 . 
   Measuring element  1  consists of motion-resisting elements  1   a  attached to arms  1   b . Measuring element  1  is attached with mounting element  1   c  to the end  2   a  of the torsion shaft  2 , which is preferably self-centering. Torsion shaft  2  is bearing-mounted inside drive shaft  5 , using bearing and sealing element  3  at the measuring end and bearing element  18  at the drive end  2   b , which element is advantageously an annular ball bearing. The outer shell of bearing  18  matches with the shoulder of sleeve  4   b   1  located on the first flange of the differential element, and is axially locked into the shoulder with clamping element  6 , which is advantageously a threaded sleeve. Element  3 , either slide bearing or roller bearing, is combined with sealing elements  3   a  to prevent the entry of process media into the device. Calibration equipment  27 , including pulling groove  27   a , are incorporated in the end of the torsion shaft. A calibration brake (not shown) can be inserted into groove  27   a  via hole  27   b  through part  10   c , As shown in  FIG. 5 . 
   To the drive end  2   b  of torsion shaft  2  is attached the second flange  4   a  of the differential element  4 , the flange including a slot plate  4   e . Slot plates  4   e , located on the outer shells of flanges  4   a  and  4   b , consist of a thin plate with a great number of radial slots (not shown). The first flange  4   b  of differential element  4  is located next to sleeve  4   b   1 , which is positioned coaxially inside rotor  8 , so that flanges  4   a  and  4   b  and thus also slot plates  4   e  face each other. Flexible elements  4   c , e.g. springs, located between flanges  4   a  and  4   b  transmit the torsional force from rotor  8  to torsion shaft  2 . Differential elements  4  include elements  4   f  with which the tangential phase shift between slot plates  4   e  can be measured. The elements  4   f  are advantageously suitable opto-electronic or electromagnetic sensors, the signal of which is converted with electronic control devices  26  to correspond to the currently effective torque. Elements  4   f  are attached to plate  4   d  which in turn is attached to stator body  10 . Plate  4   d  is inserted through a hole on stator body, and the hole is closed with cover  4   g  and clamping elements  4   h.    
   In one advantageous embodiment of the invention, as shown in  FIG. 5 , flexible elements  4   c  are mounted on pins  4   c   2  that are fastened to flange  4   b . Pins  4   c   2  are parallel with the longitudinal axis of the device, and they protrude through holes  4   c   1  in flange  4   a  so far that flexible elements  4   c  can be fastened to their ends. Flexible elements  4   c  are connected at their second ends in pairs to slide element  4   c   3  that is placed between them, which slide element passes through fixing pin  4   c   4  located on flange  4   a . Flexible elements  4   c  are first connected to pins  4   c   1  and to slide element  4   c   3 , which will then settle in a balanced state as determined by elements  4   c . The slide element is then locked to mounting pin  4   c   4  with clamping element  4   c   5 . Flexible elements  4   c  are positioned in such a way that they can receive and attenuate the phase shift generated between flanges  4   a  and  4   b . Holes  4   c   1  in flange  4   a  are sufficiently large in diameter so as not to hinder said phase shift. Holes  4   c   1  and pins  4   c   2  passing through them act as mechanical overload protection, protecting differential elements  4  from excessive stress. In an overload situation, pins  4   c   2  will receive stroke-like stress when hitting against the edges of holes  4   c   1 . 
   Drive shaft  5  is ad advantageously tubular in shape so that torsion shaft  2  can be positioned inside it. Drive shaft  5  is bearing-mounted in the drive shaft body  11  with bearing elements  16  and  17 . Element  16  is advantageously an annular ball bearing, and element  17  consists of a pair of angular contact ball bearings. Bearing elements  16  and  17  are sealed with sealing elements  15  and  19 . Element  15  advantageously consists of two facing radial seals, element  19  of one radial seal. Element  15  seals the device against process media and also seals the bearing lubricant inside. Element  19  prevents the entry of lubricant inside differential element  4 . At its drive end, shaft  5  is also sealed against process medium with sealing elements  13  that are located in the end piece of drive shaft body  12 . 
   Drive shaft  5  is closed at the measuring head end with a sleeve-shaped clamping element  7  attached to the shaft. Clamping element  7  is enclosed by an elastic shell  7   b  secured with clamping elements  7   c  that are placed over clamping element  7  and shaft  2 . The clamping elements  7   c  are for example locking rings. Shell  7   b  is elastic between fastening elements  7   c  and thus allows the phase shift that the measured torque generates between drive shaft  5  and torsion shaft  2 . 
   The rotor  8  of the direct drive motor is attached on the outer shell of sleeve  4   b   1  of the first differential element flange using friction mounting or mechanically closed form joint. The rotor includes ring  8   a , which contains direct drive motor control devices  8   b  that are controlled with control electronics  26 . Stator  9  is located inside stator base  10  that is positioned coaxially with the rotor. Rotor  8 , stator  9 , and control devices  8   b  are advantageously components of a commercially available frameless, brushless direct drive motor. 
   Stator base  10  consists of a sleeve-shaped body  10   b  that is enclosed using covers  10   a  and  10   c . Enclosed cover  10   c  closes the base at the drive end and is attached with fastening element  10   d , advantageously a thread. Cover  10   a  at the measuring head side is centered and fastened to body  10   b  with elements  28 . Also drive shaft body  11  is attached with elements  27  to the opposite side of cover  10   a . Cover  10   a  limits in axial direction bearing element  17 , and the above-mentioned sealing element  19  is mounted against its inner shoulder. If necessary, cooling elements such as ribs or channels (not shown) can be arranged onto the outer shell of stator base  10   b.    
   Drive shaft body  11  consists of an elongated and sleeve-like part  11   a  that is closed at the end by the end piece  12  of drive shaft body. When the device is installed to process, the outer surface of part  11   a  functions as a sealing surface. Sealing elements  11   c  are located between end piece  12  and part  11   a , and end piece  12  is fastened to the body  11  with fastening element  11   b . The fastening element  11   b  is advantageously a thread. Part  11   a  is provided with channels for sealing water or for other cooling and cleaning medium. 
   End piece  12  contains process medium sealing elements  13  that consist of ring  13   a  and rings  13   b  that limit it in both directions. Ring  13   a  rotates with drive shaft  5  while rings  13   b  remain static, whereby the facing surfaces of rings  13   a  and  13   b  provide the sealing effect. Rings  13   a  and  13   b  are made of materials suitable for end face seals. 
   Rings  13   a  and  13   b  are sealed against drive shaft  5 , end piece  12  and flange  14  using sealing elements  13   c . Annular flange  14  is located between drive shaft body  11  and end piece  12 . 
   Installation elements include coupling element  20 , insertion pipe  21 , valve  22 , sealing elements  23 , and clamping elements  24  and  25 . Coupling element  20  is advantageously a conical sleeve that can be fastened to process pipes of different sizes. Part  20  is fastened to valve  22  that consists of a first flange  22   a  and a second flange  22   c , between which the closing element body  22   b  is placed. Flanges  22   a  and  22   c  are fastened to each other with elements  25 , which are advantageously screws. The consistency transmitter can be inserted into hole  22   g  that passes through the flanges. Hole  22   g , and the body of consistency transmitter drive shaft  11 , are sealed with sealing elements  23 . Closing device  22   d , located inside the closing element body, can be moved using arm  22   f  and handle  22   e . The arm  22   f  is advantageously a threaded bar and the handle is a handwheel or other corresponding device. Closing element  22   d  is sealed between flanges  22   a  and  22   c  with suitable sealing methods (not shown) and includes plate  22   d   1  that closes hole  22   g  passing through flanges  22   a  and  22   c . The valve closes when the closing plate  22   d   1  is moved so that it fully coincides with hole  22   g . Insertion pipe  21  is attached to second flange  22   c  with elements  24 , and the consistency transmitter (body  11 ) can be pushed through the insertion pipe into an operating process. Pipe  21  is provided with pitched grooves  21   a  that reach all the way to the end of pipe  21  and function as regulating elements. A torsion arm  21   b , attached to body  11 , travels inside each groove and functions as the matching element of the regulating elements. Insertion pipe  21  is sufficiently long to ensure that body  11  closes hole  22   g  when valve  22  is open. Torsion arm  21   b , traveling in groove  21   a , receives the axial force caused by process pressure when the consistency transmitter is being installed to process or removed from it. 
   In one advantageous embodiment of the invention, the regulating element is thread  21   a  constructed on the outer shell of body  11 , while pegs  21   b  placed in the thread act as the matching elements. Insertion pipe  21  is split longitudinally so that it can be clamped around the outer shell of body  11  using clamping collars (not shown). The consistency transmitter can then be steplessly screwed deeper into the required distance by using for example a trapezoidal thread  21   a.    
   One device according to the invention functions as follows: Consistency transmitter is inserted into insertion pipe  21  in such a way that torsion arm  21   b  is in groove  21   a . Torsion arm  21   b  is turned in the groove until the transmitter body  11  is deep enough to close hole  22   g . Valve  22  is opened, and the axial force caused by the process pressure will be effective on the transmitter. Torsion arm  21   b  is turned further, and the transmitter moves against process pressure. The torsion arm is turned until the device reaches the required insertion depth in the process, after which it is secured in position with locking devices (not shown). The consistency transmitter can be extracted from process in reverse order. The transmitter is operated by means of control and automation equipment that is advantageously located in a separate housing. A direct drive motor ( 8 ,  9 ) rotates the measuring element  1  at a program-selectable rotation speed that is set and controlled by control electronics  26  according to the prevailing process conditions. The rotation of measuring element  1  can also be reversed with a program for cleaning or calibration purposes. Torque is transmitted from drive shaft  5  to torsion shaft  2  through flexible elements  4   c  located between flanges  4   a  and  4   b . The process medium resists the rotation and causes a phase shift, dampened by elements  4   c , between torsion shaft  2  and drive shaft  5 . This phase shift is measured with the help of slot plates  4   e  of differential elements using opto-electronic or electromagnetic devices, and it is further converted by a program into a signal corresponding to the measured variable, such as consistency. Drive shaft  5  rotates at the speed of the direct drive motor, receiving the loss torque caused by bearings  16  and  17  and sealings  13 ,  15  and  19 , which thus cannot affect the measurement results. In demanding process conditions this loss torque can be relatively large. Thus the measured phase shift includes the torque generated by the process medium and the losses caused by the torsion shaft bearing and sealing elements ( 3   a ,  18 ,  7   b ). These losses are very small, as the relative motion of the torsion shaft and the elements in contact with it is small. Said losses can also be reduced by dimensioning the torsion shaft so that its diameter is as small as possible. 
   The drawings and description are only intended to illustrate the present invention. Its details may vary within the limits set by the attached claims and by the description of the invention. For example, the structure of sealing elements  13  may differ from that described above, depending on the manufacturer. Moreover, it is clear to the man skilled in the art that embodiments of the invention may vary within the operating environment, customer needs, and solutions adopted in manufacturing.