Abstract:
A system for monitoring the condition of impulse lines to a differential pressure sensor. The lines may be connected at two locations of a pressure source, such as a pipe having a fluid flow. One line may direct a pressure of the source to one side of a piezoelectric diaphragm and another line may direct another pressure to the other side of the piezoelectric diaphragm. The diaphragm may provide an electrical indication of the differential pressure between both sides of the diaphragm. One of the lines may also be connected to a piezoelectric diaphragm of a static pressure sensor. The latter diaphragm may provide an electrical indication of static pressure. Detection and comparison of noise levels of the electrical indications of the pressures may indicate if one or both lines are plugged, and which one if not both.

Description:
BACKGROUND  
       [0001]     The invention pertains to sensing devices and particularly to pressure sensing devices. More particularly, it pertains to diagnosis of pressure sensing devices.  
         [0002]     In differential pressure sensors, one common field problem is the plugging of impulse lines. These lines are pipes or tubes that connect the sensor to the differential pressure producing element. In some cases, a blockage of the impulse line can create a pressure in the line that, when measured by the pressure differential reading of the sensor, will be on-scale thereby indicating normal operation while the process being monitored may have changed flow rates substantially. Despite the apparent normal operation, the sensor may actually be providing an erroneous output and reading. An illustrative example of such pressure sensor may be disclosed in U.S. Pat. No. 6,041,659, issued Mar. 28, 2000, to Douglas W. Wilda et al., entitled “Methods and Apparatus for Sensing Differential and Gauge Static Pressure in a Fluid Line”, which is hereby incorporated by reference in the present specification.  
       SUMMARY  
       [0003]     The present invention may detect abnormal operation of the differential pressure sensor despite the appearance of normal operation. This undetected abnormal operation may be due to one or more plugged impulse lines. A comparison may be made of noise from the differential pressure sensor and noise from a static pressure sensor on the same line or pipe. Comparison results may indicate which line is blocked or if both are blocked. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0004]      FIG. 1  is an illustrative example of a differential and static pressure sensor system with three lines to the measured pressure source;  
         [0005]      FIG. 2  is an illustrative example of an integrated differential and static pressure system with two lines to the pressure source;  
         [0006]      FIG. 3  is a sectional view of a differential and static pressure device;  
         [0007]      FIG. 4  is an end view of the device in  FIG. 3 ;  
         [0008]      FIG. 5   a  is a block diagram of digital diagnostic electronics for a pressure sensor system line monitor;  
         [0009]      FIG. 5   b  is a block diagram of analog diagnostic electronics for a pressure sensor system line monitor;  
         [0010]      FIG. 6  reveals a configuration of line connections of the differential and static pressure devices for the system line monitor; and  
         [0011]      FIG. 7  is a table show diagnostic results based on noise levels of signals from the pressure sensor system. 
     
    
     DESCRIPTION  
       [0012]     An illustrative differential pressure sensor  11  is shown in  FIG. 1 . It may have a tube or line  12  connected to a flange or fitting  14  connected to an end of a pipe  15 . A tube or line  13  may similarly be connected to another flange or fitting  16  connected to an end of a pipe  17 . A spacer or orifice plate  18  may be placed between flanges  14  and  16  with bolts  19  or the like holding the flange  14 , spacer  18  and flange  16  together. Flanges  14  and  16  may be attached to the ends of pipes  15  and  17 , respectively, with a weld, brazed bead, machined thread, or other like fastening approach. Tubes  12  and  13  may be fitted on to holes in flanges  14  and  16 , respectively, with similar fastening techniques. The holes may reach down into the flow area of pipes  15  and  17 . The diameter and area for flow through pipes  15  and  17 , flanges  14  and  16 , and spacer  18  may be the same.  
         [0013]     Pressures may be measured through tubes  12  and  13  via the holes in flanges  14  and  16 , respectively, to the flow area of the pipes. Another tube  21  may be attached to pipe  17  with a hole to the flow region of the pipe. Likewise, pressure may be measured through tube  21  pipe via the hole in pipe  17 . At the other ends of tubes  12  and  13  not connected to the flanges is differential pressure sensor  11 . The other end of tube  21  not connected to pipe  17  may be connected to a pressure sensor  22 . Pressure sensor  22  may measure absolute pressure or gauge pressure of the flow  24  downstream from differential pressure sensor  11 . On the other hand, tube  21  may be inserted into pipe  15  for an upstream flow pressure measurement. Incidentally, it may be desirable to measure static pressure as gauge pressure rather than absolute pressure since it may be easier to calibrate sensors using an atmospheric pressure rather than a vacuum as a reference pressure. However, the present diagnostics system may be used with absolute or gauge static pressure measurements.  
         [0014]     Electrical circuitry of the present invention, i.e., the differential pressure sensor impulse line monitor, may be designed to operate with currents of no more than 3.8 milliamps, voltages of no more than 12 volts, and power of no more than 50 milliwatts. Electrical signals representative of the sensed differential pressure may be conveyed from sensor  11  via a wire or optical fiber to a processor within the sensor  11  housing. Electrical or optical signals representative of the sensed gauge or absolute pressure may be conveyed from sensor  22  via a wire or optical fiber to the processor in sensor  11 . Transmission of these electrical signals from sensor  22  to  11  may instead be sent to the processor in the sensor  11  housing. On the other hand, signals from sensor  11  may be sent to a processor in the sensor  12  housing. An external processor may used. At output line  69  may be the results from the processor sent to a computer, display, process equipment, system or the like for diagnostic review, storage, system control, computations and/or review. Signal transmission may be by non-wireless (e.g., wire or optical fiber) or wireless (e.g., RF or IR) and in a variety of digital or analog formats.  
         [0015]     Another pressure measurement approach in lieu of tube  21  connected to pipe  17  could be having the upstream  23  or downstream  24  flow pressure measurement, whether gauge or absolute, taken from tube  12  or  13 , respectively, with a pressure sensor similar to sensor  22  situated within a structure like that of pressure sensor  20 , as shown in  FIG. 2 . Transmission of signals representative of the differential pressure and gauge or absolute pressure may be sent to a processor within the sensor  20  housing. An external processor may be used. At output line  69  may be the results from the processor sent to a computer, display, process equipment, system or the like for diagnostic review, storage, system control, computations and/or review. Signal transmission may be by non-wireless (e.g., wire or optical fiber) or wireless (e.g., RF or IR) and in a variety of digital or analog formats.  
         [0016]     An illustrative example of a differential pressure sensor and static pressure system  20  is shown in  FIGS. 3 and 4 . A sensor header  25  may include a substantially cylindrical package  26  having a first end  27  and a second end  28  with a decreased diameter waist area  29  in between, as shown in  FIG. 3 . A recessed circuit board  31  may be mounted near the first end  27  and a plurality of electrical connection pins  32  may extend from second end  28 . Pins  32  may extend to circuit board  31  as seen in an end view as in  FIG. 4 . Two glass tubes  33 ,  34  may be centrally located and extend through circuit board  31  into the interior of package  26 . Two piezoresistive silicon membranes or diaphragms  35 ,  36  may be mounted on respective ends of tubes  33 ,  34 , respectively, of circuit board  31 . Circuit board  31  may contain a processor for processing the various pressure measurements into diagnostic information.  
         [0017]     Glass tube  33  may have a central bore  37  and glass tube  34  may have a central bore  38 . Central bore  37  may be coupled to a first fluid port  39  which may extend to the surface of package  26  at a location  41  between first end  27  and waist  29 , as shown in  FIG. 2 . Bore  38  may be coupled to a second fluid port  42  which may extend to the surface of package  26  at a location  43  on waist  29 .  
         [0018]     Sensor header  25  may be coupled to a conventional diaphragm assembly. Each of piezoresistive silicon membranes  35 ,  36  may be provided with a respective strain gauge  44 ,  46 . First strain  44  gauge may be exposed on one side to high pressure P 1  and on the other side to low pressure P 2 . Thus, the differential voltage from the first strain gauge may be proportional to the differential pressure dP=P 1 −P 2 . Second strain gauge  46  may be exposed on one side to high pressure P 1  and on the other side to the atmosphere. Thus, the differential voltage from the second strain gauge may be proportional to the static gauge pressure P 1 gauge=P 1 −ATM. The nodes of the strain gauges may be coupled via circuit board  31  to pins  32 .  
         [0019]     Glass tubes  33 ,  34  may be mounted in the package with epoxy and their positions may be located with the aid of roll pins  47 ,  48 . Attachment of the tubes may also be done by soldering. Piezoresistive silicon membranes or diaphragms  35 ,  36  may be bonded to respective tubes  33 ,  34 , respectively, by thermoelectric (anodic) bonding. Package  26  may be made from stainless steel although other materials may be used. Illustrative instances of dimensions may include a package having an overall length of approximately 23 mm (excluding the pins), and an overall diameter of approximately 18 mm.  
         [0020]      FIG. 5   a  is a block diagram of digital diagnostic electronics for detection of blocked lines of sensor  11  or  20 . Line  51  may convey a differential pressure signal to a buffer  73  which may output a signal  74  representing the differential signal including the noise level of the differential pressure signal. Signal  74  may be sent to an analog to digital converter (ADC) circuit  75 . Output  58  may go to a logic circuit  60 , which may be incorporated in the sensor housing. Since the pressure sensitivities of the two sensors are different, the noise level would be normalized for each sensor within logic circuit  60  so that a meaningful comparison can be made.  
         [0021]     Line  52  may convey a static pressure signal to a buffer  83  which may output a signal  84  representing the static pressure signal and the noise level of the static pressure signal. Signal  84  may go to an ADC circuit  85 . Output  88  may go to a logic circuit  60 . Again, since the pressure sensitivities of the two sensors are different, the noise level would be normalized for each sensor within logic circuit  60  so that a meaningful comparison may be made.  
         [0022]      FIG. 5   b  is a block diagram of analog diagnostic electronics for detection of blocked lines of sensor  11  or  20 . Line  51  may convey a differential pressure signal to a buffer and filter  53  which may output a signal  54  representing the noise level of the differential pressure signal. Signal  54  may represent the level of an RMS, peak, or peak-to-peak or other representative value of the noise. Signal  54  may be sent to a comparator-like circuit  55 . Also input to circuit  55  from a reference source  57  is a signal  56  representing the normal noise level of a signal from differential pressure sensor functioning normally with impulse lines  12  and  13  open. Three outputs from circuit  55  may occur. Output  58  of circuit  55  may indicate that the noise signal  54  is greater than, about equal to, or less than the normal noise level signal  56 . Thresholds and hysteresis levels may be set for determining what is defined as greater, equal or less, and how much certain values need to change in order to return to previous indications, respectively. Output  58  may go to a logic circuit  60 , which may be incorporated in the sensor housing. Since the pressure sensitivities of the two sensors are different, the noise level would be normalized for each sensor so that a meaningful comparison can be made.  
         [0023]     Line  52  may convey a static pressure signal to a buffer and filter  63  which may output a signal  64  representing the noise level of the static pressure signal. Signal  64  may represent the level of an RMS, peak, or peak-to-peak or other representative value of the noise. Signal  64  may go to a comparator-like circuit  65 . Also input to circuit  65  from a reference source  67  is a signal  66  representing the normal noise level of a signal from static pressure sensor  22  functioning normally with impulse lines  12  and  13  open. Three outputs from circuit  65  may occur. Output  68  of circuit  65  may indicate that the noise signal  64  is greater than, about equal to or less than the normal noise level signal  66 . Output  68  may go to a logic circuit  60 . Again, since the pressure sensitivities of the two sensors are different, the noise level would be normalized for each sensor so that a meaningful comparison can be made.  
         [0024]     Logic circuit  60  may take inputs and output a diagnostic signal  69  indicating whether both lines  12  and  13  are blocked, one line is blocked and which one, or no lines are blocked. Circuit  60  may be designed to interface appropriately with digital or analog input signals. Output signal  69  may go to a computer, display, process equipment, system or the like for diagnostic review, storage, system control, computations and/or review. Signal  69  may have other kinds of destinations. Signal transmission may be by various kinds of media and in a variety of digital or analog formats.  
         [0025]      FIG. 6  reveals the configuration of the line connections of the differential  11  and static  22  pressure devices within sensor enclosure  20  utilized for obtaining the illustrative diagnostic results as shown in a table  61  of  FIG. 7  based on the various noise levels on the signals from pressure devices  11  and  22 . Static pressure sensing device  22  may be connected to the high side of the flow which is through line  12 . Normal noise levels may be on signals from connections  51  and  52  from the differential pressure  11  and static pressure  22  diaphragms  35  and  36  along with strain gauges  44  and  46 , respectively, when lines  12  and  13  are open and sensor  20  is operating in a normal fashion. If the noise level of the signal on connection  51  from the differential pressure  11  diaphragm is greater (↑) than the normal noise level and the noise level of the signal on connection  52  from the static pressure  22  diaphragm is less (↓) than the normal noise level, then line  12  may be blocked and line  13  may be open. If the noise level of the signal on connection  51  from the differential pressure  11  diaphragm is greater than the normal noise level and the noise level of the signal on connection  52  from the static pressure  22  diaphragm is about equal (--) to the normal noise level, then line  12  may be open and line  13  may be blocked. If the noise level of the signal on connection  51  from the differential pressure  11  diaphragm is less than the normal noise level and the noise level of the signal on connection  52  from the static pressure  22  diaphragm is less than the normal noise level, then lines  12  and  13  may be blocked.  
         [0026]     Although the invention has been described with respect to at least one illustrative embodiment, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.