PROCESS VARIABLE MEASURING AND DISPLAY DEVICE

Abstract: This invention relates to the field of process variable measuring and display devices. This invention can be used to measure and display any process variable, including pressure, temperature, volume, and flow rate. Specifically, this invention relates to an electronic process variable measuring device electronically coupled to a process variable display device which displays both a bar graph trend indication of the process variable and a digital display of the process variable. In a preferred embodiment, the process variable display device is totally self-contained, including the battery operated power supply.

Description: Title : PROCESS VARIABLE MEASURING AND DISPLAY DEVICE Field of the Invention This invention relates to the field of process variable measuring and display devices. This invention can be used to measure and display a process variable or indicia, including pressure, temperature, volume, and flow rate. Specifically, this invention relates to an elec¬ tronic process variable measuring device electronically coupled to a process variable display device which dis¬ plays both a bar graph trend indication of the process variable and a digital display of the process variable. Description of the Prior Art The measurement of process variables or parameters, including but not limited to flow, volume, temperature, and pressure, has long been important in industrial facil¬ ities where fluid is stored, pumped, heated, and/or pres¬ surized. Such industries include petrochemical, power generation, geophysical exploration and production, and food processing. In many industrial applications, it is desirable to display the measured process variable at a location remote from where the process variable is measured. Accordingly, process instrumentation has evolved into process measuring and display devices wherein the display device is remotely located from the measuring device. In many applications, adverse environmental conditions necessitate having a process display device remotely located from the process measuring device. Early process instrumentation was mechanical in nature. Examples of mechanical process instrumentation included floats for measuring level, pitot tubes to measure flow rate, and hydraulic devices for measuring pressure. Such mechanical devices have limited accuracy and are subject to phenomena such as hysteresis and SUBSTITUTE SHEET temperature effects, which further limits their depend¬ ability. Another drawback of mechanical process variable measuring devices is the limitation upon how remotely they can be located from a transducer. For instance, in the case of a bourbon tube for measuring pressure, the inter¬ nal volume of fluid in the bourbon tube places a practical limit upon the distance between the bourbon tube and its associated transducer. Safety concerns may also limit the degree to which mechanical process variable measuring devices such as bourbon tubes may be separated from process variable display devices. In many applications, the process variable measuring device and the process variable display device are connected by pressurized lines or hoses. Such pressurized lines or hoses present safety hazards in certain instances. Environmental transients, such as changes in tempera¬ ture, can also affect the accuracy of instrument readings wherein a pressurized line or hose of hydraulic fluid connects the process variable instrument to the trans¬ ducer. Prior art process variable display devices have appeared in the form of gauges wherein an analog reading is given by a needle, such as by a D'arsonval movement. Such needle gauge displays tend to give an unsteady or erratic reading, particularly during the measurement of dynamic processes such as discharge pressure at the outlet of a positive displacement pump. The reading on such needle gauges is also affected by other dynamic phenomena such as hysteresis and are generally slow in response due to the inertia of the movement itself. With the advent of liquid crystal display (LCD) tech¬ nology, the needle gauge has been replaced in some appli¬ cations with a multi-segment bar graph, each segment com- prised of a liquid crystal element. Such LCD analog dis¬ plays, when coupled with mechanical process variable measuring devices, are subject to many of the same inaccu SUBSTITUTESHEET racies and limitations as needle gauges. The resolution of multi-segment bar graph displays using LCD technology is a function of the number of LCD segments in the display for a given process variable range. The greater the num- ber of segments in the multi-segment display, the greater the resolution of the display. Prior art multi-segment bar graphs have utilized multiplexing in order to minimize the number of electrical connections that must be input into the multi-segment bar graph display. Although multi- plexing reduces the number of electrical connections, it also reduces voltage contrast. For instance, in a tri- plexed, multiplexed system, the voltage contrast is reduced by a factor of three. Digital displays have been used with process variable measuring devices to give a more precise indication of the magnitude of the process variable being measured. When coupled with mechanical process variable measuring devic¬ es, such digital displays are inaccurate and unstable, particularly during the measurement of dynamic processes. Digital displays utilizing both LCD and LED technolo¬ gy have become more common in recent years. Electricity is necessary to power such displays. Many prior art instruments using LED's or LCD's have relied upon AC power supplies or house current. Such reliance is often unde- sirable in environments where house current may be inter¬ rupted due to adverse environmental conditions such as lightning strikes, earthquakes, or tornados. This is particularly undesirable on offshore drilling and produc¬ tion platforms where lightning strikes and other inclement weather conditions are common. In many applications, it is highly desirable that process variable display devices be visible with the human eye in less than optimal light conditions or from distanc¬ es in excess of 35 feet. The visibility of multi-digit LCD displays is enhanced by increasing the size of the digits and by increasing the color contrast of the LCD display. In order to increase both the size and color SUBSTITUTE SHEET contrast of LCD digits, the voltage contrast input into the multi-digit LCD must be increased. The magnitude of voltage contrast needed to power LCD digits that would be visible by the human eye from a dis- tance of over 35 feet is greater than the voltage contrast produced in multiplexed systems. Thus, prior art process variable display devices have failed to combine both multi-segment bar graphs and multi-digit LCD's visible by the human eye from a distance of over 35 feet, because the voltage contrast requirements of each display are differ¬ ent. SUMMARY OF THE INVENTION The present invention relates to a process variable measuring and display device with superior accuracy, versatility, dependability, and display capabilities. Superior accuracy is achieved by using an electronic process variable measuring device rather than a mechanical process variable measuring device. The electronic process variable measuring device of the present invention is not subject to the distance, accuracy and sensitivity limita¬ tions of hydraulic devices. The electronic process vari¬ able measuring device of the present invention does not require pressurized lines or hoses and thus avoids the safety problems inherent with such pressurized lines and hoses. The electronic process variable measuring device of the present invention is more versatile than mechanical measuring devices such as hydraulic lines. It can be used to measure pressure in high pressure environments, such as the choke manifold on a drilling rig. The electronic process variable measuring device of the present invention is not adversely affected by rapid temperature or pressure changes as are hydraulic process variable measuring devices. The dependability of the present invention is superi¬ or to that of the prior art due to the ability of the present invention to run on battery power rather than AC power or house current. AC power supplies may be inter¬ rupted by adverse environmental conditions. The present invention comprises a portable power supply or portable power pack which is sealed in a casing capable of protect¬ ing the power supply from adverse environmental conditions such as wind, rain, seawater, and abrasive or corrosive chemicals. The process variable measuring device of the present invention operates on low current, thereby permit- ting the use of a portable power supply which, in a pre¬ ferred embodiment, can provide normal operating power for at least 20 months. The superior display capabilities of the process variable display device of the present invention are achieved by using both a multi-segment bar graph display to indicate the trend of the process variable being measured and a multi-digit LCD to provide an accurate reading of the process variable being measured. The stability and accuracy of both displays is superior to that of prior art instruments which rely upon mechanical, rather than electrical, process variable measuring devic¬ es. The multi-segment bar graph display and the multi- digit LCD of the present invention are configured such that they can be read with the human eye from a distance of over 35 feet. This superior display capability is achieved by providing high color contrast on both the bar graph and multi-digit LCD displays and by providing large digits on the multi-digit display. Both of these displays are contained within a housing along with the portable power supply. The present invention overcomes the problem of com¬ bining a multiplexed display with a multi-digit LCD requiring a large voltage contrast by utilizing custom designed analog to digital converters (ADC's) for each display. Specifically, the process variable display device of the present invention comprises a first ADC with digit SUBSTITUTE SHEET drive capabilities configured to receive a process vari¬ able input signal from a process variable measuring device, a second ADC with bar graph driving capabilities configured to receive a process variable input signal from a process variable measuring device, a multi-digit LCD electronically coupled to receive an input signal from the first ADC, and a multi-segment bar graph electronically coupled to receive an input signal from the second ADC. Thus, each display is separately driven by an ADC that is configured to receive a process variable input signal from a process variable measuring device. A preferred embodiment of the present invention com¬ prises a portable power supply operatively coupled to supply power to the first and second ADC's, the multi- digit LCD, and the multi-segment bar graph. The portable power*supply also provides power to the sensor components, including a Wheatstone bridge. This power supply is capa¬ ble supplying power to these components for at least 20 months. Thus, this preferred embodiment of the present invention is superior to all prior art process variable display devices that are dependent upon AC power or house current for reasons previously discussed herein. In another preferred embodiment, the process variable display device of the present invention is housed in a substantially cylindrical body with a removable display face through which the multi-segment bar graph display and the multi-digit LCD can be read. This cylindrical body is dimensionally configured such that it can easily fit into spaces in commercially available instrument panels where prior art process variable display devices are presently installed. Thus, the process variable display device of the present invention is configured to easily replace prior art process variable display devices without requir¬ ing a replacement or modification of existing instrument panels. The present invention is also directed toward a process variable measuring and display device comprising SUBSTITUTESHEET a process variable measuring device capable of producing an electronic process variable input signal that is proportional to the magnitude of the measured process variable, a direct drive ADC electronically coupled to receive an electronic process variable input signal from the process variable measuring device, a multiplexed ADC electronically coupled to receive an electronic process variable input signal from the process variable measuring device, a multi-digit LCD electronically coupled to receive an input signal from the direct drive ADC, and a multi-segment bar graph display electronically coupled to receive an input signal from the multiplexed ADC. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a block diagram of several embodiments of the present invention. FIGURE 1 also includes FIGURES 1A- 1J which depicts the display drive waveforms, FIGURES 1A-C the direct drive and FIGURES 1D-J the multiplexed wave¬ forms. FIGURE 2 is a schematic diagram of several embodi¬ ments of the present invention depicting a physical embodiment of the multi-segment bar graph display and the multi-digit LCD. FIGURE 3A is an exploded front view of the process variable display device. FIGURE 3B is an exploded side view of the process variable display device in its housing. FIGURE 3C is a cutaway top view of the portable power pack of the present invention. FIGURE 4A is an isometric view of the process vari¬ able measuring device in it casing. FIGURE 4B is a side cutaway view of a preferred embodiment of the process variable measuring device. FIGURES 5 and 6 depict a block diagram of a fully digital embodiment of the sensor and display units, respectfully, of the present invention. SUBSTITUTE SHEET DESCRIPTION OF A PREFERRED EMBODIMENT As shown in FIGURE 1, the process variable measuring device of the present invention comprises a first ADC with digit drive capabilities 14 configured to receive a process variable input signal from a process variable measuring device 10, a second ADC with bar graph drive capabilities 18 configured to receive a process variable input signal from a process variable measuring device 10, a multi-digit LCD 22 electronically coupled to receive an input signal from the first ADC 14, and a multi-segment bar graph 26 electronically coupled to receive an input signal from the second ADC 18. FIGURE 1 also includes FIGURES 1A-1J which depicts the display drive waveforms, FIGURES 1A-C the direct drive and FIGURES 1D-J the multiplexed waveforms. Figure 1A depicts the backplane waveform of the direct drive cir¬ cuit, while FIGURES IB and 1C depict the "ON" and "OFF" segment waveforms, respectively. The waveforms of FIGURES 1A-C cooperate to make LCD segments visible or non-visible in a manner known in the art. FIGURES 1D-F depict the "ON," "OFF," and "UNIQUE" backplane waveforms. The ON and OFF backplane waveforms cooperate in a manner similar to that described with regard to FIGURES 1A-C to "activate" (make visible) indi- vidual segments of the multi-segment bar graph display and the UNIQUE backplane waveform ensures that all segments from zero to the maximum segment activated remain visible. The "ON" and "OFF" segment waveforms of FIGURES 1G-H pro¬ vide variations in contrast of the multi-segment bar graph. This configuration minimizes pin overhead from the bar graph driving ADC. Finally, FIGURES II-J are included for completeness but are not used in the display 26; they may be used, for example, in activating indicators or enunciators, such as low battery voltage. A preferred embodiment of the present process vari¬ able display device is depicted in FIGURE 2. As shown in FIGURE 2, the multi-segment bar graph 26 has at least 42 ε UESTITUTE SHEET segments. In the most preferred embodiment, the multi- segment bar graph 26 has 101 segments. As further shown in FIGURE 2, the multi-digit LCD 22, comprises at least three digits, each of which are at least 3/4" high. This display permits viewing the process variable from at least about 35 feet. This display provides an additional advan¬ tage in that it is viewable from about 30° either side of an axis perpendicular to the plane of the display. Assume that the face of the display is the face of a clock. If the display is tilted toward the viewer (i.e., viewing from 12 o'clock), the display is viewable up to 15° of tilt. If the display is tilted back away from the viewer, to the left, or to the right, (i.e., viewing from 6, 3, and 9 o'clock respectively), the display is viewable up to 30° of tilt, with the optimum viewing angle at 6 o'clock. As further shown in FIGURE 2, the second ADC 18 is multiplexed. The first ADC 14 is a direct drive ADC, as shown in FIGURE 2. In a preferred embodiment, the first and second ADC's are semiconductor chips, manufactured by Harris Semiconductor, having model Nos. ICL7136 and ICL7182, respectively. These semiconductor chips are operable on a current of less than 1 milliampere, thus facilitating the battery powered operation of the present invention for periods of at least 20 months without replacing the battery pack. In a preferred embodiment, the present invention com¬ prises a portable power supply 9A operatively coupled to supply power to the first ADC 14, the second ADC 18, the multi-digit LCD 22, and the multi-segment bar graph 26. In a preferred embodiment, portable power supply 9A is sealed in a casing 9B capable of protecting it from adverse environmental conditions, as shown in FIGURE 3B. As shown in FIGURE 3C, the portable power supply 9A com¬ prises a plurality of individual batteries 15 a-b and 16 a-b enclosed within the casing 9B. The portable power supply 9A housed in casing 9B constitutes a portable power pack. In a preferred embodiment, portable power pack 9B SUBSTITUTE SHEET is operatively coupled to supply normal operating power to direct drive ADC 14, multiplexed ADC 18, bar graph display 26, and multi-digit LCD 22 for a period of at least 20 months. Portable power pack 9B is configured in a preferred embodiment to supply a voltage of at least seven volts, as shown in FIGURE 3C. In a preferred embodiment, portable power pack 9B comprises two pairs of lithium batteries 15A & 15B and 16A & 16B, connected in parallel. The batteries in each pair of batteries are connected in series. As shown in FIGURE 3C, battery 15A is connected in series with battery 15B and battery 16A is connected in series with battery 16B. In a preferred embodiment, portable power supply 9A comprises an internal fuse that greatly reduces the probability of explosion if the batteries are short circuited. The battery may preferably be a Tadiran® lithium inorganic battery (Type TL-2300) or an Electrochem CSC lithium oxyhalide primary cell (Series CSC93, 3B35). When configured as shown in FIGURE 3C, the batteries pro- vide an average of about 7.23 volts and 28 ampere hours. In a preferred embodiment, the bar graph display 26, multi-digit LCD 22, and portable power pack 9B are con¬ tained within a housing 20 as depicted in FIGURES 3A and 3B. Portable housing 20 comprises a substantially cylin- drical body 19 and a removable face 25 through which bar graph display 26 and multi-digit LCD 22 can be read. Removable face 25 is secured to cylindrical body 19 by a multiplicity of fasteners. In one preferred embodiment, three fasteners 27 are equidistantly spaced in the outer peripheral region 24 of removable face 25. In another preferred embodiment, four fasteners 23 are equidistantly spaced in the outer peripheral region 24 of removable face 25. In a preferred embodiment, the present invention co - prises a process variable measuring device 10 capable of producing an electronic process variable input signal that is proportional to the magnitude of the measured process SUBSTITUTESHEET variable, as shown in FIGURES 2 and 4B. Process variable measuring device 10 provides an input signal to direct drive ADC 14 and multiplexed ADC 18. In a preferred embodiment, process variable measuring device 10 is a pressure sensor such as the piezoresistive pressure sensor manufactured by KELLER PSI of Hampton, Virginia, comprising a force collector 13 capable of being deflected in an amount proportional to a pressure applied against it and a strain gauge 11 mechanically coupled to force collector 13. Strain gauge 11 is configured to pro¬ duce an electronic output signal proportional to the deflection of force collector 13, as shown in FIGURES 2, 4A, and 4B. As shown in FIGURE 4A, the cylindrical compo¬ nents depicted are a part of the Wheatstone bridge shown in FIGURE 2. In a preferred embodiment, strain gauge 11 comprises a Wheatstone bridge configured to produce a differential voltage electronic output signal as shown in FIGURE 2. The electronic voltage output signal of Wheatstone bridge 11 is a differential voltage signal. The force collector 13 serves to protect the extremely delicate Wheatstone which is embedded in the silicon substrate of the inte¬ grated circuit. As the force collector detects a stress, it transmits this information (through a silicone coupler in the preferred embodiment) to the Wheatstone bridge. This transmitted force flexes the Wheatstone bridge, creating an imbalance in the bridge. This imbalance is seen as a ratiometric shift in the two voltage outputs from the bridge. FIGURES 5 and 6 together depict an overall block diagram of an embodiment of the present invention that includes fully digital operation with microprocessor con¬ trol. The circuit includes the process variable measuring device 10 including the bridge circuit 11 and the compara- tor 12. A power supply 9B provides power to the various components. The circuit also includes an ADC ( "A/D" ) 31 which is preferably located in vicinity of the sensor. SUBSTITUTE SHEET The ADC 31 provides a digital signal to a microprocessor 30 that processes the digital signal in a manner previous¬ ly described. In this way, the communication link between the sensor and the display portions of the invention is digital and therefore much more immune to noise and other effects. The microprocessor 30 provides the processed digital signal to a differential driver 32 that drives a differential receiver 34 over a sensor link 36. The microprocessor serves the additional functions of compen- sating for manufacturing variations from one sensor to another and accommodating temperature variations. The driver 32 and receiver 34 provide sufficient power to drive the components of FIGURE 6 and buffer the various voltage levels. The differential receiver 34 provides the digital signal to a microprocessor 38 which processes the signal for reception by a digital to analog ("D/A") con¬ verter 40. The microprocessor 38 also provides the timing control for communication with the microprocessor 30 and provides the capability with communicating directly with external devices such as personal computers over an exter¬ nal digital link 41. The D/A converter 40 provides an analog signal to a set of LCD drivers 42 that drive the LCD display 44. Preferably the LCD display 44 includes the displays 22 and 26 on a single laminate, while each of the displays 22 and 26 has its own display circuitry. Many modifications and variations may be made in the embodiments described herein and depicted in the accompa¬ nying drawings without departing from the concept of the present invention. Accordingly, it is clearly understood that the embodiments described and illustrated herein are illustrative only and are not intended as a limitation upon the scope of the present invention. SUBSTITUTESHEET

Claims: WE CLAIM : 1. A process variable display device capable of reading a process variable input signal from a process variable measuring device, comprising: a. a first ADC with digit drive capabilities configured to receive a process variable input signal from a process variable measuring device; b. a second ADC with bar graph driving capabilities configured to receive a process variable input signal from a process variable measuring device; c. a multi-digit LCD electronically coupled to receive an input signal from said first ADC; and d. a multi-segment bar graph electronically coupled to receive an input signal from said second ADC. 2. The process variable display device of claim 1, wherein said first ADC is a direct drive ADC. 3. The process variable display device of claim 1, wherein said second ADC is a multiplexed ADC. 4. The process variable display device of claim 1, wherein said multi-segment bar graph has at least 42 segments. 5. The process variable display device of claim 1, wherein said multi-digit LCD comprises at least three digits, each of said digits being at least 3/4" high. 6. The process variable display device of claim 1 further comprising a portable power supply electronically coupled to supply normal operating power to said first and second ADC's, said multi-digit LCD, and said multi-segment SUBSTITUTESHEET bar graph, said portable power supply being capable of supplying said power for at least 20 months. 7. The process variable display device of claim 6, wherein said portable power supply is sealed in a casing capable of protecting said portable power supply from adverse environmental conditions. 8. A process variable display device capable of reading a process variable input signal from a process variable measuring device comprising: a. a direct drive ADC configured to receive a process variable input signal from a process variable measuring device; b. a multiplexed ADC configured to receive a process variable input signal from a process variable measuring device; c. a multi-digit LCD electronically coupled to receive an input signal from said direct drive ADC; d. a bar graph display having at least 42 segments electronically coupled to receive an input signal from said multiplexed ADC; e. a portable power pack, operatively coupled to supply normal operating power to said direct drive ADC, said multiplexed ADC, said bar graph display, and said multi-digit LCD, said portable power pack being capable of supplying said power for at least 20 months; and f. a housing containing said bar graph display, said multi-digit LCD, and said portable power pack. 9. The process variable display device of claim 8, wherein said portable power pack supplies a voltage of at least 7 volts. 10. The process variable display device of claim 8, wherein said housing comprises a substantially cylindrical body and a removable display face through which said bar graph display and said multi-digit LCD can be read. 11. The process variable display device of claim 10, wherein said removable face is secured to said body by three fasteners spaced equidistantly in the outer periph- eral region of said face. 12. The process variable display device of claim 10, wherein said removable face is secured to said body by four fasteners spaced equidistantly in the outer peripher- al region of said face. 13. The process variable measuring and display device of claim 8, wherein said first ADC and said second ADC are operable on a current of less than 1 milliampere. 14. A process variable measuring and display device comprising: a. a process variable measuring device capable of producing an electronic process variable input signal that is proportional to the magnitude of a measured process variable; b. a direct drive ADC electronically coupled to receive an electronic process variable input signal from said process variable measuring device; c. a multiplexed ADC electronically coupled to receive an electronic process variable input signal from said process variable measuring device; SUBSTITUTE SHEET d. a multi-digit LCD having digits at least 3/4" high, said multi-digit LCD electronically coupled to receive an input signal from said direct drive ADC; and e. a multi-segment bar graph display electronically coupled to receive an input signal from said multi- plexed ADC. 15. The process variable measuring and display device of claim 14, wherein said process variable measuring device is a pressure sensor comprising: a. a force collector capable of being deflected in an amount proportional to a pressure applied against the collector; and b. a strain gauge mechanically coupled to said force collector, said strain gauge configured to produce an electronic output signal proportional to the deflection of said force collector. 16. The process variable measuring and display device of claim 15, wherein said process variable measuring device is housed in a casing that protects said process variable measuring device from adverse environmental conditions. 17. The process variable measuring and display device of claim 15, wherein said strain gauge comprises a Wheatstone bridge, said Wheatstone bridge configured to produce a differential voltage as said electronic output signal. 18. The process variable measuring and display device of claim 14, wherein said process variable measuring device is a pressure sensor comprising a Wheatstone bridge, said Wheatstone bridge being configured to produce an electron- ic output signal proportional to the pressure measured by said pressure sensor. SUBSTITUTESHEET 19. The process variable measuring and display device of claim 18, wherein said electronic output signal is a differential voltage signal. 20. The process variable measuring and display device of claim 13, wherein said first ADC and said second ADC are operable on a current of less than 1 milliampere. 21. Process indicia instrumentation comprising: (a) a force collector configured to deflect a dis- tance proportional to pressure applied to the collector, the pressure indicative of a process indicia; (b) a strain gauge coupled to the collector to produce an analog electric output signal propor- tional to the defection of the collector; (c) a first analog to digital converter to receive the analog signal and develop a digital repre- senta ion of the process indicia; (d) a first display to display the digital represen- tation; (e) a second analog to digital converter to receive the analog signal and develop a trend represen- tation of the process indicia indicative of the rate of change of the process indicia; and (f) a second display to display the trend represen- tation. 22. The instrumentation of claim 21 wherein the first display is a liquid crystal display. 23. The instrumentation of claim 21 wherein the first display is a light emitting diode display. 24. The instrumentation of claim 21 wherein the second display is a bar graph display. SUBSTITUTE SHEET 25. The instrumentation of claim 21 wherein the first analog to digital converter is a direct drive converter. 26. The instrumentation of claim 21 wherein the second analog to digital converter is a multiplexed converter. 27. The instrumentation of claim 21 wherein the instru- mentation is portable and further comprising a portable, sealed power supply. SUBSTITUTESHEET

Inventors: DE SILVA JON DOUGLAS, MCLATCHY RICHARD C, DE SILVA, JON, DOUGLAS, MCLATCHY, RICHARD, C.
Applicants: HOUSTON DIGITAL INSTR INC, HOUSTON DIGITAL INSTRUMENTS, INC.
Application year: 1992
Main classification: G01R13
IPC codes: G01D7, G01L19