Patent Publication Number: US-6903659-B2

Title: Low power regulator system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a Divisional of U.S. application Ser. No. 09/796,902, filed Feb. 28, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/603,157, filed Jun. 23, 2000 now U.S. Pat. No. 6,441,744 which claims priority to Provisional Application Ser. No. 60/141,576, filed Jun. 29, 1999. 

   FIELD OF THE INVENTION 
   The present invention generally relates to a flow regulator and more particularly to a low power regulator system and method that selectively powers on and powers off selected regulator components to reduce power consumption. 
   BACKGROUND OF THE INVENTION 
   In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce and control the pressure of a fluid. Regulators are typically used for these tasks by providing adjustable flow restriction through the regulator. The purpose of the regulator in a given application may be to control flow rate or other process variables, but the restriction inherently induces a pressure reduction as a by-product of its flow control function. 
   By way of example, a specific application in which regulators are used is the distribution and transmission of natural gas. A natural gas distribution system typically includes a piping network extending from a natural gas field to one or more consumers. In order to transfer large volumes of gas, the gas is compressed to an elevated pressure. As the gas nears the distribution grid and, ultimately, the consumers, the pressure of the gas is reduced at pressure reducing stations. The pressure reducing stations typically use regulators to reduce gas pressure. 
   It is important for natural gas distribution systems to be capable of providing sufficient volumes of gas to the consumers. The capacity of this system is typically determined by the system pressure, piping size, and the regulators, and system capacity is often evaluated using a simulation model. The accuracy of the system model is determined using flow data at various input points, pressure reducing points, and output points. The pressure reducing points significantly impact the capacity of the gas distribution system, and therefore it is important for the system model to accurately simulate the pressure reducing points. The pressure reducing points, however, are within the distribution system and therefore are not considered custody transfer points (i.e., points at which the control of gas flow switches from the distribution system to the consumer). As a result, flow measurement is typically not provided at the pressure reducing points. Furthermore, since the pressure reducing points are not custody transfer points, the added cost of high accuracy is not required. Flow measurement problems similar to those described above with respect to natural gas distribution are also present in other regulator applications (i.e., industrial processes, chemical processes, etc.). 
   In addition, regulators are subject to failure due to wear during operation, thereby reducing the ability to control pressure along a pipeline. A damaged regulator may allow fluid to leak, thereby increasing fluid waste and possibly creating a hazardous situation. While damaged regulators may be repaired or replaced, it is often difficult to detect when a regulator has failed and determine which regulator is damaged. Detecting a failure and determining which regulator has failed is more difficult in a typical natural gas delivery system, where pipelines may run several miles. 
   Prior art regulators are typically operated such that all or most of the regulator components remain powered on at all times. In those cases where a prior art regulator is powered by a battery source, operating such prior art regulators often results in an unnecessary drain in power resources thereby reducing the efficiency of the regulator. In addition, as the regulator battery capacity is reduced as a result of prolonged use or perhaps as a result of a malfunction, continuing to operate a prior art regulator with all or most of the regulator components powered on shortens the time that such a prior art regulator can be operated. 
   SUMMARY OF THE INVENTION 
   In accordance with an aspect of the invention, a method is provided for collecting sensor data in a pressure regulator system including a controller and a plurality of sensors where the controller is configured to collect sensor data. The method includes the steps of placing the controller in a first mode and issuing a first controller command to activate a selected sensor from the plurality of sensors. The controller is placed in a second mode for a first predetermined period of time where the controller consumes a reduced amount of power in the second mode than when operating in the first mode. The controller is placed in the first mode again after the first predetermined period has lapsed. A second controller command is issued to collect sensor data from the selected sensor. 
   In accordance with an alternative aspect of the invention, a method is provided for collecting sensor data in a pressure regulator system including a controller and a plurality of sensors, where the controller is configured to collect sensor data from each of the plurality of sensors during a sampling period. The method includes the steps of activating a first selected sensor of the plurality of sensors, collecting sensor data from the first selected sensor and then deactivating the first selected sensor. A second selected sensor of the plurality of sensors is then activated. Sensor data is collected from the second selected sensor and then the second selected sensor is deactivated. 
   In accordance with another aspect of the invention, a pressure regulator is provided for controlling fluid in a pipeline where the pressure regulator is operated by a battery. The pressure regulator includes a battery sensor, a memory and a controller. The battery sensor is adapted to sense an operation parameter of the battery and generate an operation parameter signal. The memory is adapted to store a threshold capacity value of the battery and generate a threshold capacity signal. The controller unit controls the power consumption of the pressure regulator. More particularly, the controller is adapted to receive the operation parameter signal and the threshold capacity signal and generate a command signal to operate the pressure regulator in at least one of a plurality of operating modes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the several figures, and in which: 
       FIG. 1  is a schematic diagram illustrating a regulator with flow measuring apparatus in accordance with the present invention. 
       FIG. 2  is a schematic diagram of an additional embodiment of a regulator incorporating flow measuring apparatus. 
       FIG. 3  is a perspective view of the regulator flow measurement apparatus. 
       FIG. 4  is a side elevation view, in cross-section, of regulator flow measurement apparatus in accordance with the teachings of the present invention. 
       FIG. 5  is a flow chart schematically illustrating a user-specified limit portion of an alarm routine. 
       FIG. 6  is a flow chart schematically illustrating a logic alarm sub-routine. 
       FIGS. 7A-7E  are flow charts schematically illustrating specific portions of the logic alarm sub-routine. 
       FIG. 8  is a block diagram representation of low power circuitry for the gas flow regulator. 
       FIG. 9  is a flow chart schematically illustrating the overall operation of the low power circuitry. 
       FIG. 10  is a flow chart schematically illustrating the initialization process as implemented by the low power circuitry. 
       FIG. 11  is a flow chart schematically illustrating an example of a sampling sequence adapted to conserve battery power as implemented by the low power circuitry. 
       FIG. 12  is a flow chart schematically illustrating a method of determining an operating mode for the gas flow regulator. 
       FIG. 13  is a flow chart schematically illustrating a method of placing the gas flow regulator in a first power conservation mode. 
       FIG. 14  is a flow chart schematically illustrating a method of placing the gas flow regulator in a second power conservation mode. 
       FIG. 15  is a flow chart schematically illustrating a method of placing the gas flow regulator in a fail safe mode. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a preferred embodiment of a fluid pressure regulator, such as a gas pressure regulator  10 , in accordance with the invention. The illustrated gas pressure regulator  10  includes gas flow measuring apparatus as will be described hereinafter wherein upstream pressure, downstream pressure, and orifice opening measurements are used to calculate flow and other information. It is to be understood that a liquid pressure regulator also may be provided in accordance with the principles of the invention, as the illustrated gas pressure regulator is merely one example of a fluid pressure regulator according to the invention. 
   The regulator shown in  FIG. 1  includes a regulator body  12 , a diaphragm housing  14 , and an upper housing  16 . Within the regulator body  12 , there is provided an inlet  18  for connection to an upstream pipeline and an outlet  20  for connection to a downstream pipeline. An orifice  22  inside the regulator body  12  establishes communication between the inlet  18  and the outlet  20 . 
   A diaphragm  26  is mounted inside the diaphragm housing  14  and divides the housing  14  into upper and lower portions  14   a ,  14   b . A pressure spring  28  is attached to a center of the diaphragm  26  and is disposed in the lower portion of the diaphragm housing  14   b  to bias the diaphragm  26  in an upward direction. 
   A stem  30  is attached to and moves with the diaphragm  26 . A throttling element, such as a valve disc  32 , is attached to a bottom end of the stem  30  and is disposed below the orifice  22 . The valve disc  32  is sized to completely block the orifice  22 , thereby cutting off communication from the inlet  18  to the outlet  20 . Accordingly, it will be appreciated that the pressure spring  28  biases the valve disc  32  in an upward direction to close the orifice  22 . The valve disc  32  is formed with a varying cross-section so that, as the valve disc  32  moves downwardly, the unblocked (or open) area of the orifice  22  gradually increases. As a result, the open area of the orifice  22  is directly related to the position of the valve disc  32 . 
   Gas pressure in the upper chamber of the diaphragm  14   a  is controlled to move the valve disc  32  between the closed and open positions. Pressure in the upper portion of the housing  14   a  may be provided in a number of different manners. In the present embodiment, pressure in the upper portion  14   a  is controlled by a loading pilot (not shown). However, the regulator  10  may be of a type which uses a different type of operator, such as an unloading pilot, or the regulator  10  may be self-operated or pressure-loaded, without departing from the scope of the present invention. 
   A further alternative for controlling the gas pressure in the upper portion of the diaphragm housing  14   a  includes a first tube running from the upstream piping to the upper portion of the diaphragm housing  14   a , with a first solenoid controlling gas flow therethrough. A second tube is also provided which runs from the upper portion of the diaphragm housing  14   a  to the downstream piping and has a second solenoid disposed therein to control flow therethrough. A PC is connected to the first and second solenoids to control their operation. To increase pressure in the upper portion of the diaphragm housing  14   a , the first solenoid is opened to allow upstream pressure into the upper portion, thereby driving the diaphragm  26  downward to open the orifice  22 . Gas may be exhausted through the second solenoid to thereby reduce pressure in the upstream portion  14   a  and raise the diaphragm  26 , thereby closing the orifice  22 . Regardless of the manner of providing and controlling pressure, it will be appreciated that increased pressure moves the diaphragm  26  and attached valve disc  32  downward to open the orifice  22  while decreased pressure closes the orifice  22 . This arrangement is given by way of example only, and is not intended to limit the scope of the present invention, as other arrangements well known in the art may also be used. 
   In accordance with certain aspects of the present invention, pressure sensors are provided upstream and downstream of the throttling element to measure upstream and downstream pressure levels P 1 , P 2 . As illustrated in  FIG. 1 , the first and second pressure sensors  34 ,  35  are mounted to the upper housing  16 . Tubing  36  extends from the first pressure sensor  34  to tap into piping located upstream of the regulator inlet  18 . Additional tubing  37  extends from the second pressure sensor  35  to tap into piping located downstream of the regulator outlet  20 . Accordingly, while the first and second pressure sensors  34 ,  35  are mounted on the upper housing  16 , the tubing  36 ,  37  communicates upstream and downstream gas pressure, respectively, to the first and second pressure sensors  34 ,  35 . In the alternative, the first and second pressure sensors  34 ,  35  may be located directly in the upstream and downstream piping with wiring running from the pressure sensors to the upper housing  16 . To provide for temperature correction, if desired, a process fluid temperature transmitter  48  is located in the upstream piping which measures process temperature. 
   The upper housing  16  further includes a sensor for determining valve disc position. According to the illustrated embodiment, the stem  30  is attached to the valve disc  32  and is connected to the diaphragm  26 . A travel indicator  40 , which is preferably an extension of the stem  30 , extends from the diaphragm and into the upper housing  16 , so that the position of the valve disc  32  corresponds to the position of the valve disc  32 . The sensor, therefore, comprises an indicator travel sensing mechanism, preferably a Hall effect sensor. The Hall effect sensor includes a Hall effect magnet  42  attached to an upper end of the travel indicator  40 . A magnet sensor  44  is disposed inside the upper housing  16  for sensing the location of the Hall effect magnet  42 . By detecting the position of the magnet  42 , the location of the valve disc  32  and hence the open area of the orifice  22  may be determined. A second travel indicator (not shown) may be linked to the travel indicator  40  to provide visual indication of valve disc travel. The second travel indicator runs upwardly from the travel indicator  40  and through the upper housing  16  to extend above a top surface of the upper housing  16 . 
   An alternative for measuring travel of the valve disc  32  is the use of a radar transceiver (not shown) disposed above the travel indicator  40  in the upper housing  16 . The radar transceiver detects the position of the travel indicator  40  and transmits a signal indicating travel indicator position. 
   It will be appreciated that the position of the valve disc  32  may be determined in a number of different manners in addition to the magnet  42  and sensor  44  embodiment described above. For example, a laser sensor (not shown) may be provided either in the upper housing  16  to measure the position of the travel indicator  40 , or in the diaphragm housing  14  for directly measuring the position of a portion of the diaphragm  26 . When the laser sensor is in the latter position, the travel indicator  40  is not needed. In addition, an ultrasonic sensor may be used to determine valve disc position. 
   A further alternative, illustrated at  FIG. 2 , measures loading pressure in the upper portion of the diaphragm housing  14   a  to infer valve disc position. It will be appreciated that the position of the valve disc  32  varies with the pressure present in the upper portion  14   a  of the diaphragm housing. In this embodiment, a loading pressure sensor  46  is provided in the upper housing  16  for measuring pressure at the upper portion of the diaphragm housing  14   a . The measured loading pressure may then be used to determine valve disc position. 
   Returning to the embodiment of  FIG. 1 , the first and second pressure sensors  34 ,  35  and the travel sensor  44  provide output which is fed into an electronic flow module  50 . The electronic flow module  50  may be provided integrally with the regulator, such as in the upper housing  16  as illustrated in  FIG. 1 , or may be remotely positioned. The inlet pressure, outlet pressure and valve disc position are used to determine flow through the variable orifice of the regulator  10 . For sub-critical gas flow, the flow rate is calculated using the algorithm:
 
 F =SQRT{{ K SUB1}OVER{ G*T}}*K sub2 *Y*P sub 1*sin  K sub3SQRT{{ P sub1 −P sub2}OVER} P sub20
 
, where
         F=flow rate,   K 1 =absolute temperature constant,   G=specific gravity of the flow media,   T=absolute temperature of the flow media,   K 2 =stem position constant,   Y=stem position,   P 1 =absolute upstream pressure,   K 3 =trim shape constant, and   P 2 =absolute downstream pressure.       

   The stem position and trim shape constants K 2 , K 3  are specific to the particular size and type of regulator, and are primarily dependent on the specific trim size and shape. As those skilled in the art will appreciate, the product of K 2  and Y may be equivalent to a traditional flow sizing coefficient. The above algorithm is suitable for calculating sub-critical (i.e., P 1 −P 2 &lt;0.5P 1 ) gas flow rate through linear, metal trim valve type regulators. 
   For critical gas flows, the calculation is modified by eliminating the sine function. For other types of regulators, such as non-linear metal trim and elastomeric style regulators, a similar algorithm is used, however the stem position constant K 2  becomes a function related to pressure drop ΔP (i.e., the difference in upstream and downstream pressures P 1 −P 2 ) and/or valve stem position, as is well known in the art. For liquid flow, the equation becomes:
 
 F =SQRT{{ K SUB1}OVER{ G*T}}*K sub2 *Y *SORT{ P sub1 −P sub2}
 
,where
         F=flow rate,   K 1 =absolute temperature constant,   G=specific gravity of the flow media,   T=absolute temperature of the flow media.   K 2 =stem position constant,   Y=stem position,   P 1 =absolute upstream pressure, and   P 2 =absolute downstream pressure.       

   A similar calculation is used in the embodiment of  FIG. 2 , which measures loading pressure in the upper portion of the diaphragm housing  14   a  to infer valve disc travel, except a loading pressure constant K 4  and a gauge loading pressure P L  replace the stem position constant K 2  and the stem position Y values. The loading pressure constant K 4  is also application specific and must be determined for each type of regulator  10 . For non-linear elastomeric throttling members, the loading pressure constant K 4  is a function of ΔP and P L . 
   In the preferred embodiment, a local flow view module  52  is also disposed inside the upper housing  16 . The local flow view module  52  includes an electronic flow totalizer which provides totalized flow information. The local flow view module  52  further has an output port which allows access by a hand-held communication device to access the totalized flow and reset the local flow totalizer for future use. In the currently preferred embodiment, the local flow view module  52  includes an LCD readout enclosed inside the upper housing  16 . A cap  17  attached to the top of the upper housing  16  has a clear plastic window which allows the LCD readout to be viewed. 
   A communication module  54  transmits flow data to an auxiliary communication device  55 , such as a remote terminal unit (RTU), a PC, or any other device capable of interrogating the regulator controls. The communication module  54  may include an antenna  53  for transmitting flow information to a remote meter reading system (not shown). A power module  56  is also provided for powering the flow measurement mechanism. The power module  56  is capable of providing regulated voltage for the entire device, and may be supplied by any well known source such as solar, battery, and DC or AC power sources. 
   It will be appreciated that the electronic flow module  50 , local flow view module  52 , communication module  54 , and power module  56  may be separately provided as illustrated in  FIG. 1 , or may be provided on a single main circuit board located inside the upper housing  16 . 
   The calculated flow rate through the regulator  10  may be quickly and easily calibrated using a separate flow meter  58 . The flow meter  58 , which may be a turbine or other type of meter, is temporarily inserted into the downstream pipeline to measure actual fluid flow. The flow meter  58  provides feedback to an auxiliary communication device  55  (RTU, PC, etc.) or directly to the main circuit board. The feedback may be used to generate an error function based on observed flow conditions which is then incorporated into the flow calculations performed by the regulator  10 , thereby to provide more accurate flow data. 
   A currently preferred embodiment of regulator flow measurement and diagnostic apparatus is illustrated in  FIG. 3 , generally designated by reference numeral  100 . As shown in  FIG. 3  the apparatus  100  includes a cylindrical body  101  having a first end  102  adapted for connection to a regulator (not shown). As with the previous embodiments, the regulator is disposed in a fluid flow passage having an upstream section and a downstream section. The cylindrical body  101  encloses a travel indicator  103  ( FIG. 4 ) which is connected to a diaphragm (not shown) in the regulator. According to the illustrated embodiment, a Hall effect sensor is used to detect the position of the travel indicator  103 . A portion  104  of the travel indicator  103  is formed of magnetic material having pole pieces. A hall element  105  ( FIG. 4 ) is positioned to detect the magnetic material portion  104  and generate a position signal according to the position of the travel indicator  103 . 
   A housing  106  is attached to the cylindrical body  102  and has a first pressure port  107 , a second pressure port  108 , an auxiliary pressure port  109 , and an auxiliary port  110  (FIG.  3 ). A first pressure sensor assembly  111  is inserted inside the first pressure port  107 , and a tube (not shown) connects the assembly  111  to the upstream section of the flow passage. A second pressure sensor assembly  114  is inserted into the second pressure port  108 , and a tube (not shown) connects the second assembly  114  to the downstream section of the flow passage. A third pressure sensor assembly  115  may be inserted into the auxiliary pressure port  109  for measuring at a third pressure point. The third pressure sensor  115  may be used to measure pressure at a variety of locations, including in the flow passage or in the regulator to infer plug travel, as described in greater detail above with regard to the previous embodiment. In a preferred embodiment, a fourth pressure port  117  is provided for measuring atmospheric pressure. The auxiliary port  110  is provided for receiving discrete or analog input from another device, such as the temperature transmitter  48  illustrated in FIG.  1 . In addition, an I/O port  112  is provided for connection to an outside device, as described in greater detail below. 
   A plurality of circuit boards  120   a-e  are disposed inside the housing  105  for controlling various operations of the apparatus  100  (FIG.  5 ). In the illustrated embodiment, a first (or main) circuit board  120   a  may include an interface for the first, second, third pressure sensors, and atmospheric pressure sensors, and a connection for the hall effect sensor  105 . A second (or communication) circuit board  120   b  provides an interface for communication with outside devices. The second circuit board  120   b  may include connection for wired transmission, such as a modem card, an RS232 communication driver, and a CDPD modem. In addition or alternatively, a transceiver may be provided for wireless communication. A third (or main) circuit board  120   c  preferably includes a processor, a memory, a real-time clock, and communication drivers for two communication channels. The processor may include, among other things, one or more of the algorithms noted above for calculating flow rate, while the memory may store selected parameters, such as the high and low pressures for each day. An optional fourth circuit board  120   d  provides an interface for the auxiliary I/O device  55 . Examples of such I/O devices may include leak detectors, methane detectors, temperature sensors, and level sensors. A fifth (or termination) board  120   e  is also provided having a power supply regulator, field termination (for connection to I/O devices), a back-up power supply, and connections into which the other boards  120   a-d  may plug into. While five circuit boards  120   a-e  are shown in the illustrated embodiment, it will be appreciated that a single circuit board, less than five circuit boards, or more than five circuit boards may be used without departing from the scope of the invention. 
   It will be appreciated, therefore, that communication between the apparatus  100  and an outside device may be by RF modem, ethernet or other known communication like. The processor allows the outside devices to enter information such as desired pressure set points and alarm conditions into the apparatus  100 , and retrieve data stored in the memory. The data retrieved may include the alarm log and stored operational parameters. For instance, the retrieved information may include a history of upstream and downstream pressures stored periodically in memory, so that the apparatus  100  provides the function of a pressure recorder. 
   In accordance with certain aspects of the present invention, the processor includes a routine for generating alarm signals. A first portion of the routine compares measured parameters (i.e., the upstream pressure, downstream pressure, and travel position) to certain user-specified limits, as schematically illustrated in FIG.  5 . In addition, one or more logic sub-routines may be run which compares at least two of the measured parameters and generates an alarm signal based on a specific logical operation, examples of which are schematically shown in FIGS.  6  and  7 A- 7 D. 
   Turning first to the level alarms, a check is initiated  150  to determine whether any level limits have been entered by the user. The pressure, travel, flow, and battery values are first compared to user entered high-high limits  151 . If any of the values exceeds the high-high limits, the date and time are read  152  and a corresponding high-high alarm is logged  153 . Next the measured values are compared to user entered high limits  154 . If any of the values exceeds the high limits, the date and time are read  155  and a corresponding high alarm is logged  156 . The values are then compared to user entered low limits  157 . If any of the values is lower than a user entered low limit, the date and time are read  158  and a corresponding low alarm is logged  159 . Finally, the values are compared to user entered low-low limits  160 . If any of the values is lower than a low-low limit, the date and time are read  161  and a corresponding low-low alarm is logged  162 . 
   Additional limit alarms may be set based on the calculated flow rate F. For example, a user may enter limits for instantaneous and accumulated flow. When the calculated flow rate F exceeds either of these limits, an alarm is triggered. A further alarm may be provided based on stem travel. The user may enter a limit for accumulated stem travel distance and trigger a maintenance alarm when accumulated stem travel exceeds the limit. 
   After checking the user-entered limit alarms, one or more logic sub-routines may be run to determine if any logical alarm conditions exist. In the preferred embodiment, each of the logic sub-routines is combined into a single, integrated logic sub-routine as generally illustrated in FIG.  6 . As shown in  FIG. 6 , the sub-routine begins by collecting all the pressure and travel data, in calculating the flow  165  through the pressure regulator. Each of the measured parameters is then compared to both the other measured parameters and any user-specified set points. The logical alarms are monitored for upstream pressure  166 , downstream pressure  167 , auxiliary pressures  168 , stem travel  169 , and flow rate  170 . Additional logical alarms may also be provided for feedback from the third pressure sensor assembly and auxiliary device connected to the I/O connection  112 . After obtaining the relative values of each of the parameters, the logical alarms are then checked, as described in greater detail below. 
   A preferred sequence of operations for determining logical alarms based on upstream pressure (step  166 ) are schematically shown in FIG.  7 A. First, the sub-routine checks for an entered value relating to upstream pressure  172 . If a value is entered relating to upstream pressure, the sub-routine determines whether the measured upstream pressure must be greater than  173 , less than  174 , or equal to  175  the user-entered value. For each relative comparison (i.e., steps  173 ,  174  and  175 ), a series of sub-steps are performed as illustrated in  FIGS. 7B-7D . 
   If an alarm requires the upstream pressure to be greater than a certain value, the sub-routine first checks for a specific upstream pressure value entered by the user  176  (FIG.  7 B). If the user has entered a value for upstream pressure, the measured upstream pressure is compared to that entered value  177 . If the measured value is greater than the entered value, the upstream pressure greater than flag is set  178 . If no specific user-entered value is used, the sub-routine checks to see if downstream pressure is to be compared to the upstream pressure  179 . If so, the sub-routine determines if the upstream pressure is greater than the downstream pressure  180 . If so, the upstream pressure greater than downstream pressure flag is set  181 . If downstream pressure is not used as a logical alarm, the sub-routine next checks for a logical alarm value based on auxiliary pressure  182 . If auxiliary pressure is used as a logical alarm, the sub-routine checks whether upstream pressure is greater than the downstream pressure  183 . If so, the upstream pressure greater than auxiliary pressure flag is set  184 . 
   As illustrated in  FIGS. 7C and 7D , the sub-routine performs similar steps to determine if upstream pressure is less than or equal to a logical alarm value  185 - 202 . Furthermore, operations identical to those shown in  FIGS. 7B-7D  are performed for the downstream and auxiliary pressures to determine whether they are greater than, less than, or equal to specified logic alarm values. Since these operations are identical, separate flow charts illustrating these steps are not provided. 
   Turning to logic alarms based on travel  169  (FIG.  7 A), a logic sequence flow chart is illustrated at FIG.  7 E. Accordingly, the sub-routine first checks whether a travel position logic value has not been entered  203 . If a traveled position logic value has been entered, the sub-routine determines whether the measured value must be greater than the logic value  204 . If the logic operator is a greater than limit, the sub-routine determines whether the measured traveled position is greater than the entered value  205 . If so, the travel greater than flag is set  206 . If no “greater than” limit is used for travel, the sub-routine then checks for a “less than” limit  207 . If a “less than” limit is detected, the sub-routine determines if the measured travel is less than the entered value  208 . If so, the travel less than flag is set  209 . If a “less than” value is not used, the sub-routine checks for an “equal to” operator limit  210 . If an “equal to” limit is used, the sub-routine determines whether the measured travel equals the entered value  211 . If so, the travel equal to flag is set  212 . A similar sequence of steps may be used to determine if the calculated flow rate is greater than, less than, or equal to a logic flow alarm value, as called for at step  170  of FIG.  6 . 
   Based on the logic flags which may be set, certain logic alarms may be triggered based on a comparison of two of the measured parameters. For example, a shut off problem alarm may be set to trigger when travel position equals zero and downstream pressure is increasing (present downstream pressure is greater than immediately preceding measured downstream pressure). When the appropriate operational conditions exist to set the corresponding logic flags, the shut off problem alarm is triggered, which may indicate that fluid is leaking through the pressure regulator possibly due to damage to the throttling element. Another logic alarm may be generated when the travel value is greater than zero and the downstream pressure signal is decreasing, which may indicate a broken stem. Yet another logic alarm may be generated when the travel value is greater than zero and the upstream pressure signal is increasing, which may also indicate a broken stem or other problem with the regulator. A further logic alarm may be triggered when the travel signal is greater than zero and the downstream pressure signal is greater than a user entered downstream pressure limit, which may indicate a problem with the pilot which controls the regulator. Other logic alarms may be entered which take into account the various measured and calculated values, so that other potential problems with the regulator may be immediately indicated. 
   The memory associated with the processor preferably includes an alarm log which tracks the date, time, and type of alarm. The alarm log is accessible by an outside communication device to allow an alarm history to be retrieved. Furthermore, the processor preferably includes a report by exception (RBX) circuit which automatically communicates any alarm conditions to a remotely located host computer. Accordingly, potential problems in the pipeline are quickly reported, and the particular component or damaged area is identified. 
   The gas flow regulator  10  is typically powered by a battery power source and is specifically adapted to minimize the amount of power consumed. Referring to  FIG. 8 , a low power circuit  300  engineered for minimum power consumption either by low static power consumption or by utilizing switched duty cycle operation is shown. The gas flow regulator  10  includes a low power circuitry  300  where individual components of the low power circuitry are normally placed in a sleep mode and powered on as they are needed to perform measurement or diagnostics operations. The low power circuit  300  generally includes the processor board  120   c  communicatively coupled to the communications board  120   b  and to the sensor I/O board  120   a . The processor board  120   c  is also adapted to support an expansion  10  board  302 . 
   The processor board  120   c  includes a processor  303  that is communicatively coupled to a real time clock (RTC) module  306 , a communications module  308 , a local operator interrupt (LOI) module  310 , an internal input output (I/O) module  312 , an external static random access memory (static RAM) module  314  and an electronic erasable programmable read only memory (EEPROM) module  316 . Each of the modules  306 - 316  may be disposed on individual printed circuit boards or one or more printed circuit boards. 
   The processor  303  includes a CPU  304  an internal clock  318 , a flash read only memory (flash ROM)  320  and a processor random access memory (processor RAM)  322  and provides the control and timing for communications with each of the boards  102   a ,  102   b ,  302  and modules  306 - 316  and controls the activation and power distribution to the different modules  306 - 316  and sensor  34 ,  35 ,  44 ,  115 . 
   The CPU  304  operates in three different modes: awake mode where the CPU  304  consumes the amount of power necessary to maintain full operations, sleep mode where the CPU  304  consumes a reduced amount of power that is necessary to maintain operations of its internal systems and deep sleep mode where the CPU  304  essentially shuts itself down and operates on a minimal amount of power. In sleep mode, the operating frequency of the CPU  304  is reduced to conserve power. In deep sleep mode, the CPU  304 , the internal clock  318  and the internal RAM  322  are all powered off to further conserve power. 
   The internal clock  318 , among other functions, wakes up the CPU  304  from sleep mode in accordance with the configured sample rate supplied by the operator. The flash ROM  320 , a non-volatile memory that does not require power to maintain its contents, contains the operational firmware. The processor RAM  322  is a static memory that is used for the storage of non-initialized variables and program stack. The processor RAM  322  is volatile and must be initialized on every power up. 
   The RTC module  306  performs the time of day and calendar functions that are used to stamp the logs and history, communication call out scheduling, communication power control and alarming based on time of day and calendar. The RTC module  306  communicates with the CPU  304  via a I 2 C bus and an external interrupt bus INT 1 . Prior to entering deep sleep mode, the CPU  304  typically issues instructions to the RTC module  306  to issue an external interrupt INT 1  to wake it up at a designated time that is based on the configured sampled rate. 
   The communication module  308  includes a RS485 driver that is adapted to communicate with external devices or tools that may be multi-dropped on a single RS485 loop. An interrupt signal generator, within the communication module  308  issues an interrupt signal TNT 2  to the CPU  304  when external communication is requested. This interrupt signal INT 2  causes the CPU  304  to activate the RS485 driver enabling two way communication between the processor and the external device or tool. If the CPU happens to be in sleepmode or deep sleepmode, the interrupt signal wakes up the CPU  304 . 
   The LOI module  310  includes a RS232 driver and is intended for connection to a configuration tool on-site. When the LOI module  310  senses activity indicating that external communications are being requested, an interrupt signal INT 3  is issued to the CPU  304 . If the CPU  304  happened to be in sleep mode or deep sleep mode, the interrupt signal INT 3  wakes up the CPU  304 . Upon receiving the interrupt signal INT 3 , the CPU  304  powers up the LOI module including the RS232 driver to enable two-way communication with the configuration tool. 
   The internal I/O module  312  is communicatively coupled to the CPU  304  via a processor analog port A 1 . The CPU  304  regulates the power to the internal I/O module. The internal I/O module  312  is normally in a sleep mode to conserve power and is only powered on prior to and during the conversion of internal I/O signals. The internal I/O module  312  is configured to supply the CPU  304  with internal parameter data including board temperature, the voltage applied to the power terminals and the logic battery voltage. The logic battery voltage is the terminal voltage of the internal battery. The internal I/O module  312  also alerts the CPU  304  as to whether an optional communications card such as a RS 232 card, a 2400 baud modem, a CSC cell phone interface card, a Cellular Digital Packet Data cell phone interface card, a Code Division Multiple Access CDMA cell phone interface card or a radio interface card has been installed. 
   The EEPROM module  316  is used to store the configuration, calibration and security parameters for the gas flow regulator  10 . This memory is non-volatile and does not require power to maintain its contents. The static RAM module  314  is a static memory that is used to store initialized variables, alarm logs, event logs, and historical logs. A section of the static RAM Module  314  is reserved for firmware downloads such as firmware upgrades, and functionality enhancements. This facilitates the performance of security and reliability checks prior to programming the flash memory  320  with the firmware upgrades. Power to the static RAM module  314  is backed up using a replaceable lithium battery. 
   The communication board  120   b  provides an interface for external communications with one or more outside devices, including a host or a master device. The communication module  120   b  is adapted to accommodate different types of communication cards requiring the use of different types of drivers. Upon the installation of a specific communication card, an analog signal identifying the type of the communication card installed, is generated by the communication card to the CPU  304 . The CPU  304  uses the analog signal data to correctly initialize and interface to the communication driver on the communication card typically without operator intervention. The communication card includes an interrupt signal generator for issuing an interrupt signal INT 4  to issue an interrupt to the CPU  304  when communications with an external communication device is requested. Responsive to the interrupt signal INT 4  the CPU  304  to activates the driver on the communication card so that two-way communication is enabled between the external communication device and the CPU  304 . The communication board  120   b  may configured for wired communication via for example, a modem card, an RS232 communication driver or wireless communication via for example, a cellular digital packet data (CDPD) modem. The communications board  120   b  may also be adapted to interface with other devices including a dial modem, other cellular devices, a radio device, a satellite, a Fieldbus® interface or a HART® interface. 
   The sensor I/O board  120   c  includes one or more analog to digital (A/D) converters AD 1 , AD 2  to facilitate communications between the CPU  304  and the different sensors including first, second, third, and fourth pressure sensors  34 ,  35   115 ,  117  and the travel sensor  44 . The CPU  304  communicates with the A/D converters AD 1 , AD 2  via a serial peripheral interface bus SPI. The A/D converters AD 1 , AD 2  are always powered to maintain calibration data but are normally placed in a sleep mode to minimize power consumption. The CPU  304  wakes up individual A/D converters AD 1 , AD 2  as necessary to interface with individual sensors  34 ,  35 ,  44 ,  115 ,  117  to collect and convert sampled sensor readings. 
   The sensor I/O board  120   c  also includes a plurality of sensor interfaces including a first, second, third and fourth pressure sensor interfaces P 1 , P 2 , P 3 , PBAR, and a travel sensor interface TRAVEL. The CPU  304  regulates the power supplied to each of the different sensors  34 ,  35 ,  44 ,  115 ,  117  via the sensor interfaces P 1 , P 2 , P 3 , PBAR, TRAVEL. The power control data bus PCDB enables communications between the CPU  304  and the sensor interfaces P 1 , P 2 , P 3 , PBAR, TRAVEL. The sensors  34 ,  35 ,  44 ,  115 ,  117  are normally powered off and powered up only when it is necessary to take a reading or sample. The CPU  304  issues a power up command to the appropriate pressure interface when required to power a particular sensor  34 ,  35 ,  44 ,  115 ,  117 . Each sensor interface P 1 , P 2 , P 3 , PBAR, TRAVEL includes a voltage reference, a bridge amplifier and a power switch. The power switch controls the power supplied to the voltage reference, the bridge amplifier and the sensor  34 ,  35 ,  44 ,  115 ,  117 . The voltage reference powers the sensor, provides a reference input to the A/D converters AD 1 , AD 2  and provides a reference output to the bridge amplifier. The use of the reference signal at multiple points makes the low power circuit  304  ratiometric thereby reducing the effects of drift in the reference and on the accuracy of the A/D conversions. The sensor  34 ,  35 ,  44 ,  115 ,  117  may be adapted to operate in an operational mode and a sleep mode. In sleep mode, the sensors  34 ,  35 ,  44 ,  115 ,  117  consume a reduced amount of power than when in operational mode. The sensors  34 ,  35 ,  44 ,  115 ,  117  may be placed in a sleep mode when they are not actually being used to sample data to conserve power. For example, the sensors  34 ,  35 ,  44 ,  115 ,  117  may be placed in sleep mode after they have been initialized and then activated or placed in operational mode when sampled data is required by the CPU  304 . Similarly, the A/D converter may also be adapted to operate in a sleep mode and an operational mode. In an alternative embodiment the sensors  34 ,  35 ,  44 ,  115 ,  117  and the A/D converters may simply be powered off, as opposed to being placed in sleep mode, when not in use. 
   The expansion I/O  302  is typically contained on a single card that is interfaced through a single connector to an expansion serial peripheral interface SPI bus, an analog port, control outputs and status inputs. The connector also routes the field signals from the field terminations to the expansion I/O card  302 . The functionality of the expansion I/O board  302  is typically determined on an application by application basis. 
   Referring to  FIG. 9 , a flowchart providing an overview of the operation of the gas flow regulator  10  firmware running on the low power circuitry  300  is shown. The firmware is stored in the flash memory  320 . The operation of the firmware is initiated in response to a command to supply power to the low power circuitry components at step  402  where the power up command may be generated either by the CPU  304  or an operator. 
   At step  404 , the CPU  304  begins an initialization process whereby the low power circuitry  300  and the sensors  34 ,  35 ,  44 ,  115 ,  117  are initialized in accordance with an operator supplied configuration to obtain and process periodic sensor readings or samples and perform flow rate calculations. The operator can configure the gas flow regulator  10  to sample sensor data at different rates at various time intervals. 
   The CPU  304  then determines at step  406 , based on the operator supplied configuration, whether a sampling operation should be initiated. If the configuration indicates that the CPU  304  should sample the sensor readings, the CPU  304  begins by powering on selected sensors  34 ,  35 ,  44 ,  115 ,  117  and selected components of the low power circuitry  300  as they are required to obtain samples of the sensor readings from the A/D converters AD 1 , AD 2  at step  408 . Each of the sensors and the low power circuitry components are powered off as soon as they complete their role in the sampling process. The collected data includes readings from the upstream pressure sensor  34 , the downstream pressure sensor  35 , the auxiliary pressure sensor  115 , the barometric pressure sensor  117  and the travel sensor  44 . Other collected parameters include the input voltage, the battery voltage, the battery chemistry and the ambient board temperature. At step  410 , the CPU  304  uses the collected sensor data to calculate the flow rate. Then, the CPU  304  compares each of the collected readings and the calculated flow rate against operator supplied upper and lower limits to determine if any of the values are out of range or trigger an alarm condition at step  412 . The CPU  304  determines if any alarms have changed state, such as from a set alarm condition to a clear alarm condition or from a clear alarm condition to a set alarm condition and logs its findings in the alarm log. When an alarm is logged, the CPU  304  files a report by exception (RBX) and automatically communicates the alarm condition to the remotely located host computer via the communication module  120   b . Accordingly, potential problems in the pipeline are quickly reported, and the particular component or damaged area is identified 
   At step  414 , the CPU  304  determines whether each of the collected readings and the calculated flow rate should be archived based on a configured archive rate. If the CPU  304  determines that a particular parameter, such as for example a collected reading or a calculated flow rate should be archived, at step  416  the CPU  304  calculates an average value and an accumulated value for that parameter and then logs the values in the log history. The archive rate for each of the parameters are configurable by the operator and can range from archiving once a minute to once every sixty minutes. 
   If the CPU  304  determines that a particular parameter is not required to be archived, the CPU  304  adds the value of the parameter to a running sum of that parameter&#39;s values and keeps track of the number of parameter values that have been summed at step  420  in the event the CPU  304  is required to calculate an average value for that parameter. 
   Once the sampling process is complete, at step  422 , the CPU  304  issues a command to perform system checks and diagnostics. The system diagnostics process is performed to verify that the low power circuitry is operating properly, to act on any pending RBX requests, to ensure that the latest firmware configuration is being utilized, to monitor firmware updates, to monitor the battery performance and to ensure that the gas pressure regulator  10  is performing within operational limits. Specifically, the CPU  304  monitors the gas pressure regulator system power for proper operating ranges in accordance with the low alarm limits, the low-low alarm limits, the high alarm limits and the high-high alarm limits. Depending on the battery voltage levels, the configured sample rates, the internal clock rates, the RTC clock rates and the communication levels, the appropriate gas pressure regulator systems are adjusted to conserve power and increase battery life. Under very low power conditions, power may even be removed from portions of the low power circuitry  300  to further conserve power. Once the system checks are complete, the CPU  304  is placed in a sleep mode so that it operates at a reduced operating frequency thereby reducing the amount of power consumed. 
   The CPU  304  then checks the different communication systems within the low power circuitry  300 , such as the communication module  308 , the LOI module  310  and the communication board  120   b  to see if any of the communication ports are active at step  424 . If a communication port is active, the CPU  304  remains awake and returns again to step  406  to determines whether the sampling process should be repeated and performs the systems checks again at step  422 . 
   If no communication ports are active, the CPU  304  issues a command to the RTC to wake up the CPU  304  via an external interrupt INT 1  at a designated time and then enters into the deep sleep mode to conserve power at step  426 . While the CPU  304  is in deep sleep mode, the CPU  304  may be woken up via an external interrupt INT 2 , INT 3 , INT 4  issued by for example the LOI module  310 , the communication module  308  or the communication board  120   b . When the designated period of time has passed, the RTC issues an external interrupt INT 1  to the CPU  304  at step  428  and the CPU wakes up, returns to step  404  again and repeats the entire process again. 
   Referring to  FIG. 10 , the initialization process of step  404  is described in greater detail. As mentioned previously, the initialization process is activated in response to a command to supply power to the low power circuitry components at step  402 . The CPU  304  begins by configuring the different input/output ports to assign proper signal direction and default signal levels for disabling or powering down the low power circuitry hardware at step  430 . The CPU  304  also sets up the port functions for the communication board  120   c , the communication module  308 , the LOI module  310 , the A/D converters AD 1 , AD 2 , and the timers including the RTC  306 . 
   At step  432 , the CPU  304  then performs a validity check to determine whether the static RAM  314  contains a valid program configuration. Specifically, three different areas of static RAM  314  are checked for known configuration patterns. If any one of the three different areas do not match the known configuration pattern, static RAM memory  314  is considered invalid. If the static RAM memory  314  is invalid, the CPU  304  initializes the entire memory, including all of the un-initialized and initialized variables at step  434 . The static RAM memory flag is then set at step  436 . If the RAM memory  314  is valid, the CPU  304  initializes, only the un-initialized variables at step  438  and clears the static RAM memory flag at step  440 . 
   The CPU  304  then sets up a communication link with the RTC module  306  and checks the RTC  306  for proper operation at step  442 . If the RTC  306  is not operating properly or power supplied to the RTC  306  has been lost, the CPU  304  re-initializes the RTC  306  with the proper date and time functions. The CPU  304  then checks to see if a modem has been installed at step  444 . If a modem has been installed, the CPU  304  initializes the modem and then powers the modem down. The modem is powered down prior to powering up the remaining low power circuitry hardware to limit the maximum current drawn during startup. 
   At step  446 , the communication ports in the communication board  120   c , the communication module  308  and the LOI module  310  are initialized in accordance with the configured baud rate, data bits, stop bits, and parity. The interrupts INT 2 , INT 3 . INT 4  to initiate a communication via the communication ports remain disabled during the initialization process to prevent communications from being initiated during the remainder of the initialization process. Any installed modems are then configured for operation at step  448 . 
   Then at step  450 , if the static RAM  314  was found to be invalid at step  432 , the CPU  304  checks to see if a previously saved memory configuration was stored in the EEROM  316 . If a previously saved memory configuration is found, it is loaded into the static RAM  314  at step  452 . If a previously saved memory configuration was not stored in the EEPROM  316 , the CPU  304  uses default parameters to initialize the static RAM  314 . 
   At step  454 , the flash ROM parameters are initialized. Updates to the firmware stored in the flash ROM  320  are typically performed by the operator. The flash ROM parameters govern the updating process, provide error checking, and validation. Next at step  456 , the A/D converters AD 1 , AD 2  are initialized and calibrated for operation. Once the initialization process is complete, the A/D converters AD 1 , AD 2  are placed in a sleep mode to conserve power. At step  458 , the CPU  304  validates the configured sample and archive periods. The CPU  304  checks to ensure that there is at least one sample per archive period. The sample flag is set so that sampling process begins immediately after the completion of the initialization process  404 . 
   The sampling sequence employed by the gas pressure regulator  10  to sample the different I/O parameters such as the sensor readings, various low power circuitry parameters and battery power levels is specifically designed to minimize battery power consumption. Only those sensors  34 ,  35 ,  44 ,  115 ,  117  and low power circuitry components necessary to perform a sampling operation are powered on and then powered off immediately after a sample is collected by the CPU  304 . Referring to  FIG. 11 , an example of a sampling sequence employed by the CPU  304  in reading a selected set of pressure sensors  34 ,  35 ,  115  and the travel sensor  44  while minimizing battery power consumption, as may be performed at step  408  is shown. 
   The CPU begins by issuing a command to power on the A/D converters AD 1 , AD 2 , the upstream pressure sensor  34  and downstream pressure sensor  35  at step  450 . The CPU  304 , at step  452 , sets the internal clock  318  to issue a wake up signal to the CPU  304  after designated time period has passed and enters into the sleep mode. The duration of the sleep period is based on the time it takes for the pressure sensors  34 ,  35  to warm up sufficiently to provide accurate readings. An example of the duration of such a sleep period may be fifty milliseconds. Upon being woken up by the internal clock  318  at step  454 , the CPU  304  reads the appropriate A/D converters AD 1 , AD 2  to obtain a sample reading of the pressure sensors  34 ,  35 . The CPU  304  then issues a command to power off the power sensors  34 ,  35  and a command to power on the auxiliary power sensor  115  at step  456 . The CPU  304  converts the acquired samples of the upstream and downstream pressure readings into engineering units at step  458 . The CPU  304  sets the internal clock  318  to issue a wake up signal to the CPU  304  after a designated period of time has lapsed and enters into sleep mode at step  460 . When the CPU  304  is woken up by the internal clock  318  at step  462 , the CPU  304  reads the appropriate A/D converter AD 1 , AD 2  to obtain a reading from the auxiliary pressure sensor  115 . The CPU  304  then issues a command to powers off the auxiliary power sensor  115  and issues a command to power on the travel sensor  44  at step  464 . The CPU  304  converts the sample obtained from the auxiliary pressure sensor  115  into engineering units at step  466  and sets the internal clock  318  to issue a wake up signal at the appropriate time and enters into a sleep mode at step  468 . Upon waking up in response to the internal clock signal  318 , the CPU reads the appropriate A/D converter AD 2  to obtain a reading from the travel sensor  44  at step  470 . At step  472 , the CPU  304  issues a command to power off the travel sensor and then converts the travel sensor reading into engineering units at step  474 . 
   The CPU  304  is typically placed in deep sleep between sampling periods. Once the CPU  304  has completed sampling the sensors  34 ,  35 ,  44 ,  115 ,  117  and prior to entering deep sleep mode, the CPU  304  issues a command to the RTC  306  to issue an interrupt signal INT 1  to the CPU  304  to place it in awake mode, in other words in operational mode, after a predetermined period of time. The predetermined period of time corresponds to the time interval between two consecutive sampling periods and is based on the configured sampling rate. When in deep sleep mode, the CPU  304  can also be placed in awake mode in response to an interrupt signal indicating that an external communication with a communication device is being requested. 
   While the example has been described with a selected set of sensors, a sampling sequence involving the reading of a fewer number of sensors or a greater number of sensors is considered to be within the scope of the invention. For example, the CPU  304  may obtain readings from the barometric pressure sensor  117 , readings of the battery level and parameters relating to the performance of the processor board  120   c . Alternative sampling sequences involving the powering on of selected components as they are required to obtain sensor readings and then subsequently powering off of selected components may be adapted without departing from the spirit of the invention. 
   As mentioned previously, the gas flow regulator  10  is powered by a battery and has a known power demand. The gas flow regulator power demand is typically a function of the configured sample rate. In other words, the higher the sample rate of the sensors  34 ,  35 ,  44 ,  115 ,  117 , the greater the amount of power consumed. The CPU  304  monitors the battery capacity levels and can typically provide an estimated replacement date for the battery. The sensed battery chemistry is used to identify the type of battery being used to power the gas flow regulator  10 . For example, the sensed battery chemistry can be used to determine if the battery being used is a lead acid type battery or a lithium type battery. The CPU  304  determines the battery capacity remaining based on a sensed battery terminal voltage, a sensed battery chemistry and the known gas flow regulator power demand. The CPU  304  may also use data associated with environmental factors such as for example sensed battery temperature to further adjust the value of the remaining battery capacity. 
   Referring back to  FIG. 8 , the battery voltage sensor  502  and the battery chemistry detector  504  are communicatively coupled to an A/D converter AD 2 . The CPU  304  samples the data read by each of the sensors  502 ,  504  via the A/D converter AD 2 . Referring to  FIG. 12 , the gas flow regulator  10  is adapted to operate in one of four battery operating modes: a normal mode, a first power conservation mode, a second power conservation mode and a fail safe mode. The CPU  304  places the gas flow regulator  10  in the appropriate operating mode based on the remaining battery capacity. Specifically, the battery voltage sensor  502  senses the battery terminal voltage. The A/D converter AD 2  converts the sensed battery terminal voltage into a digital signal representative of the sensed battery terminal voltage. The CPU  304  reads the appropriate A/D converters AD 2  to obtain the readings of the battery terminal voltage and the battery chemistry at step  510  and determines the remaining battery capacity at step  512 . The capacity of the battery in use and a set of threshold voltages or threshold capacities are stored in memory. The CPU  304  compares the sensed battery voltage to each of the threshold capacities to determine whether to operate the gas flow regulator  10  in normal operating mode, a first power conservation mode, a second power conservation mode or in a fail safe mode. The logic unit that performs the comparison function is a component of the low power circuitry firmware. 
   At step  514 , the CPU  304  then determines if the battery is operating at a threshold capacity of greater than 25% of its full operating capacity. If the battery is operating at a threshold capacity of greater than 25%, the CPU  304  issues the appropriate commands to place the gas flow regulator  10  in normal operating mode at step  516 . If the battery is operating at a level of less than or equal to 25%, the CPU  304  determines if the battery is operating within a range of less than or equal to a threshold capacity of 25% and greater than or equal to a threshold capacity of 15% of full battery capacity at step  518 . If battery is operating within this range, the CPU  304  issues the appropriate commands to place the gas flow regulator  10  in the first power conservation mode at step  520 . 
   At step  522 , the CPU  304  determines if the battery is operating within a range of less than or equal to a threshold capacity of 15% and greater than a minimum threshold capacity of 5% of full battery capacity. If the battery is determined to be operating within this range, the gas flow regulator  10  is placed in the second power conservation mode at step  524 . At step  526 , the CPU  304  determines if the battery is operating below a minimum threshold capacity of 5% of full battery capacity. If the CPU  304  determines that the battery is operating below the minimum threshold capacity, the gas flow regulator  10  is placed in a fail safe mode at step  528 . 
   Referring now to  FIG. 13 , the commands issued by the CPU  304  to place the gas flow regulator  10  in the first power conservation mode are described. At step  530 , the rate at which sensor readings, such as pressure sensor readings and travel sensor readings, are sampled is reduced to a first power conservation level and at step  532 , the clock rate of the internal clock  318  is reduced. The low alarm is set, time stamped and logged at step  534 . The event logs, the history logs and the alarm logs are still maintained in the first power conservation mode. While in the first power conservation mode, the occurrence of certain pre-defined events may require that the clock rate be increased. Such pre-defined events include for example, an external interrupt from a communication device such as, the communication board  120   b , the communication module  308  or the LOI module  310 . At step  536 , the CPU checks to see if the clock rate is required to be increased in response to a pre-defined event. If the CPU  304  determines that the clock rate needs to be increased, the clock rate is increased until the performance of the function requiring the higher clock rate is completed at step  538 . Then the CPU  304  issues a command to reduce the clock rate again to conserve battery energy at step  540 . 
   Referring to  FIG. 14 , the commands issued by the CPU  304  to place the gas flow regulator  10  in the second conservation mode are described. At step  542 , the rate at which sensor readings, such as pressure sensor readings and travel sensor readings, are sampled is further reduced to a second power conservation level, a sample rate that is lower than the sample rate set at the first power conservation level. At step  544 , all external communications, such as communications via the communication board  120   b  are terminated. The low-low alarm is set, time stamped and logged at step  546 . The clock rate of the internal clock  318  remains at the reduced clock rate. The event logs, the history logs and the alarm logs continue to be maintained in the second power conservation mode. 
   Referring to  FIG. 15 , the commands issued by the CPU  304  to place the gas flow regulator  10  in the fail safe mode when the main battery is considered to be dead are described. As mentioned previously, the static RAM  314  is used to store the event logs, the history logs and the alarms logs. At step  548 , a back-up battery, such as a replaceable lithium battery, is activated to supply power to the static RAM  314  thereby maintaining the event logs, the history logs and the alarm logs. All of the sensors  34 ,  35 ,  44 ,  115 ,  117 ,  502 ,  504  the A/D converters AD 1 , AD 2  and the components of the processor board  120   c , including the CPU  304  are powered off at step  550  to conserve power. Only the static RAM  314  remains powered. No new data samples are taken or stored until the main battery is replaced. 
   It will be appreciated while specific battery capacity thresholds such as for example, 25%, 15% and 5% of full battery operating capacity, have been used to illustrate an embodiment of the invention, the battery capacity thresholds are operator configured values and alternative battery capacity thresholds may be configured and applied without departing from the spirit of the invention. Additionally, while the described embodiment includes four gas flow regulator operating modes, the use of a greater or fewer number of operating modes are also considered to be within the scope of the invention. 
   The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.