Abstract:
A method ( 200 ) of controlling a liquid crystal display (LCD) ( 110 ) integrated within a sensing device for operation in cold temperature is provided. The method ( 200 ) includes providing electrical power to the LCD ( 110 ), providing an electrical signal to the LCD ( 110 ) to update displayed information, measuring ( 206 ) the ambient temperature proximate the LCD ( 110 ) and making adjustments to the power and update information supplied to the LCD ( 110 ) based on the ambient temperature. Another aspect of the invention includes a field device ( 10 ) including an LCD ( 110 ), an electronic control module ( 120 ) configured to provide power and communication signals to the LCD ( 110 ), and a temperature sensor ( 112 ) coupled to the electronic control module ( 120 ). The electronic control module ( 120 ) is configured to measure the temperature proximate the LCD ( 110 ) and control power and communication supplied to the LCD ( 110 ) based on the temperature at the LCD ( 110 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Application is a Section 371 National Stage Application of International Application No. PCT/RU2006/000539, filed Oct. 19, 2006 and published as WO 2007/046731 A3 on Apr. 26, 2007. 
     BACKGROUND 
     Field devices such as process variable transmitters, are used in the process control industry to remotely sense a process variable. Field devices such as actuators, are used by the process control industry to remotely control physical parameters of a process, such as flow rate, temperature, et cetera. The process variable may be transmitted to a control room from a field device such as a process variable transmitter for providing information about the process to a controller. The controller may then transmit control information to a field device such as an actuator to modify a parameter of the process. For example, information related to pressure of a process fluid may be transmitted to a control room and used to control a process such as oil refining. 
     Process variable transmitters are used to monitor process variables associated with fluids such as slurries, liquids, vapors and gasses in chemical, pulp, petroleum, gas, pharmaceutical, food and other fluid processing plants. Process variables include pressure, temperature, flow, level, pH, conductivity, turbidity, density, concentration, chemical composition and other fluid properties. Process actuators include control valves, pumps, heaters, agitators, coolers, solenoids, vents and other fluid controlling devices. 
     SUMMARY 
     A method of controlling a liquid crystal display (LCD) integrated within a sensing device for operation in cold temperature is provided. The method includes providing electrical power to the LCD, providing an electrical signal to the LCD to update displayed information, measuring the ambient temperature proximate the LCD and making adjustments to the power and update information supplied to the LCD based on the ambient temperature. Another aspect of the invention includes a field device including an LCD, an electronic control module configured to provide power and communication signals to the LCD, and a temperature sensor coupled to the electronic control module. The electronic control module is configured to measure the temperature proximate the LCD and control power and communication supplied to the LCD based on the temperature at the LCD. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a field device of the type useful with embodiments of the present invention. 
         FIG. 2  is a flow diagram illustrating operation of a field device to extend the operation of an LCD below its rated operating temperature in accordance with an embodiment of the present invention. 
         FIG. 3  provides a list of parameters and their initial values in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow diagram of a method of reading LCD temperature in accordance with an embodiment of the present invention. 
         FIG. 5A  is a flow diagram illustrating a step of updating the LCD display in accordance with an embodiment of the present invention. 
         FIG. 5B  is a flow diagram illustrating an alternate step of updating the LCD display in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a schematic diagram of a portion of field device  10  according to one embodiment of the invention. Field device  10  includes a liquid crystal display (LCD)  110 , which is coupled to electronic control module  120 . Electronic controller module  120  includes, in one embodiment, controller  122  coupled to memory device  124  and communication port  126 . Controller  122  can be a controller, processor, application specific integrated circuitry (ASIC) or any other acceptable control device circuitry. Power circuitry  128  is coupled to controller  122 , memory  124 , and communication port  126 , as well as measurement circuitry  130  which may be a part of electronic control module  120 . 
     Power circuitry  128  receives electrical power from power source  132 . Power source  132  can be any type of suitable electrical power source including a battery, an AC power source, a process control loop, or any other device. 
     Filed device  10  includes sensor  134  coupled to electronic control module  120 . Sensor  134  provides an input signal relative to a parameter to be measured by field device  10 . Sensor  134  can include one or more sensor elements utilizing any suitable technology. Sensor  134  may be disposed integral with LCD  110 , and is electrically coupled to measurement circuitry  130  which may include known sensor input handling circuitry. Field device  10  also includes a temperature sensor  112  coupled to electronic control module  120  via measurement circuitry  130 . Temperature sensor  112  senses ambient temperature proximate LCD  110 . Temperature sensor  112  can utilize any acceptable technology including thermocouples, resistance temperature devices (RTD) and/or thermoswitches/thermostats. Temperature sensor  112  is shown electrically coupled to measurement circuitry  130  but it is to be understood that temperature sensor  112  can be in electrical communication with communication port  126  or any other communication handling circuitry including being directly coupled to controller  122  without departing from the scope of the invention. 
     Schematic diagram  100  is a functional schematic and it is to be understood that other implementations of electronic circuitry within field device  10  may be implemented without departing from the scope of the invention. For example, memory  124  and/or communication port  126  may be physically incorporated within controller  122 . Power circuitry  128  can include any embodiments of power circuitry including regulators, voltage dividers, current limiters, and the like. LCD  110  can be a commercially available device, a custom design liquid crystal display of any size or shape, and can have any manner of electrical communication with electronic control module  120  for the purposes of receiving data from electronic control module  120 . 
     LCDs such as LCD  110  have a limited temperature operation range. For example, some LCDs having an operating range that extends only to −4° F. (−20° C.). Other LCDs may have operating ranges that are specified to be higher or lower in temperature than −4° F. Embodiments of the present invention can be applied to any LCD with any operating temperature. 
       FIG. 2  is a flow diagram illustrating method  200  describing the operation of field device  10  to extend the operation of LCD  110  below its rated operating temperature in accordance with an embodiment of the present invention. In block  202 , the electronic control module  120  initializes necessary parameters for variables used in the invention. Referring briefly to  FIG. 3 , a list of parameters and their initial values are identified. For example, Sensor_Value is defined as unread, Display_Value is defined as undefined, and Dynamic_Power_Supply is defined as off. Other parameters such as Setpoint — 1 are set to values that, in one embodiment, are stored in memory  124  of electronic control module  120 . The significance of the parameters listed in  FIG. 3  will become more apparent as the function of electronic control module  120  is described in greater detail below. 
     Once the step of initializing the parameters is performed at block  202 , electronic control module  120  will read sensor value  204  from sensor  134 . Then, electronic control module  120  will read the LCD temperature from temperature sensor  112  as shown in block  206 . Once both the sensor value and the temperature value have been obtained, electronic control module  120  will update display LCD  110 , as shown in block  208 . Electronic control module  120  then cycles back to block  204  to repeat the process of reading the sensor value, receiving the temperature value, and updating the display. 
     Step  204  of reading the sensor value from sensor  134  can be accomplished in any number of ways. As described above, the sensor element may be electrically communicating with measurement circuitry  130 . Further, the step of reading the sensor value may include any number of techniques to provide a single value. As an example, electronic control module  120  may read several values from sensor  134  and perform an averaging function to eliminate or deal with hysteresis or potential spikes in sensor readings. Any acceptable routine to read and process the sensor value can be used without departing from the scope of the invention. 
       FIG. 4  is a flow diagram of method  250  that comprises step  206  of reading the LCD temperature in greater detail according to one embodiment of the invention. After beginning in block  252 , the electronic control module  120  read LCD temperature from the temperature sensor  112 . As with step  204  described above, any number of sensor input routines can be employed to provide a value for the LCD temperature. Once the LCD temperature has been read, it is compared against a Setpoint — 1 in decision block  256 . If the LCD temperature is not less than Setpoint — 1, Dynamic_Power_Supply is set to Off, Update_Interval is set to Normal and Reduced_Complexity is set to Off. At this point, the function  206  of reading the LCD temperature is completed and electronic control module  120  moves to block  274  which is the end of the routine. 
     Returning again to block  256 , if the LCD temperature is less than Setpoint — 1, the Dynamic_Power_Supply is set to On as described in block  260 . Once the Dynamic_Power_Supply is set to On, electronic control module  120  will provide additional power to LCD  110 . In one embodiment, a second LCD power source  146  is supplied, or otherwise coupled, to the LCD in addition to first LCD power source  144 . Alternatively, additional power is supplied on the first LCD power source line  144  from the power circuitry to the LCD. Additional power provided to the LCD can be diverted from other circuitry within electronic control module  120 . At lower temperatures, a number of the electrical devices within electronic control module  120  may require less power. Thus, this power can be supplied to the LCD  110  without affecting the function of any component within electronic control module  120 . Power circuitry  128  can include any type of circuitry required to divert power from other devices to the LCD display. Additionally, or in the alternative, a any suitable temperature sensitive element can be sensed, or used, to dynamically vary the power to the LCD based upon temperature. A temperature sensitive diode can be used, such that as the temperature drops, the diode voltage drops as well. The voltage drop can be sensed and more power can be supplied to the LCD drivers. 
     Once the Dynamic_Power_Supply has been set to On, in block  260 , the electronic control module  120  then moves to decision block  262  to determine whether the LCD temperature is less than Setpoint — 2. It is to be understood that in one embodiment, Setpoint — 2 is in a lower value than Setpoint — 1. For example, Setpoint — 2 in one embodiment is −15° F. (−26° C.). Setpoint — 2 can vary depending on the rated operating temperature of the LCD  110 . If the LCD temperature is not less than Setpoint — 2, electronic control module  120  moves to block  264  in which Update_Interval is set to Normal and Reduced_Complexity is set to Off. Electronic control module  120  then moves to block  274 , which represents the end of step  206  of reading the LCD temperature. 
     Returning again to block  262 , if it is determined that the LCD ambient temperature is less than Setpoint — 2, electronic control module  120  moves to block  266  and Update_Interval is set to extended. Update_Interval determines the length of time that elapses between updates of the LCD display. When the LCD ambient temperature is above Setpoint — 2, Update_Interval is set to Normal. In one embodiment, Normal has a value, or otherwise corresponds to, an update interval of three seconds. Thus, when Update_Interval is set to Normal, the LCD is updated every three seconds. Alternatively, the value assigned to Normal can be any number that provides an acceptable rate of update to the display when the LCD ambient temperature is higher than Setpoint — 1. In one embodiment, the value assigned to Extended is six seconds. Thus, when the ambient temperature at the LCD is below Setpoint — 2, the display would be updated every six seconds. The value assigned to extended can be any value which provides acceptable update rates to the LCD when the temperature is below Setpoint — 2. For example, the value assigned to Extended could be eight seconds, ten seconds, or twenty seconds. Alternatively, Extended can be set to different values, depending how far below Setpoint — 2 the LCD ambient temperature is. 
     Once Update_Interval has been set to Extended in block  266 , electronic control module  120  compares the ambient LCD temperature to Setpoint — 3 in block  268 . It should be appreciated that Setpoint — 3 is a lower temperature value then that of Setpoint — 2. In one embodiment, Setpoint — 3 is set to −28° F. (−33.3° C.). The value of Setpoint — 3 can be any value which corresponds to the point at which additional steps need to be taken beyond extending the update rate and providing additional power to the LCD as taken above. If it is determined that the LCD ambient temperature is higher than Setpoint — 3, Reduced_Complexity is turned off in step  270  and electronic control module  120  moves to step  274  which is the end of the set temperature function. 
     Returning to block  268 , if the ambient LCD temperature, however, is lower than Setpoint — 3, Reduced_Complexity  272  is set to On. The implications of having Reduced_Complexity set to On will be discussed later with respect to the process of updating the display corresponding to block  208 . Once Reduced_Complexity has been set to On in step  272 , electronic control module  120  moves to step  274 , which represents the end of the step  206  of reading the LCD temperature. 
     Referring to  FIG. 5A  flow diagram  300  provides a functional description of step  208  of updating the LCD display performed by electronic control module  120  according to one embodiment of the invention. Beginning at block  302 , electronic control module  120  moves to decision block  304  where it compares Update_Time value to Update_Interval value. Update_Time is a timer that keeps track of the amount of time that has elapsed since the last time the LCD display has been updated. If Update_Time is not equal to or greater than Update_Interval, electronic control module  120  moves to block  314  which represents the end of the update display function. Alternatively, electronic control module  120  can remain at block  304  until Update_Time is greater than Update_Interval. 
     If it is determined that Update_Time is indeed greater than Update_Interval, electronic control module  120  moves to block  306 . At block  306 , the electronic control module  120  checks to see the status of Reduced_Complexity. If Reduced_Complexity is set to Off, electronic control module  120  moves to block  308 . At block  308 , the electronic control module  120  assigns the display variable to the value of the sensor value variable. The display is then updated with all of the information that is provided normally to the display. That information includes in one embodiment, a display value, and an engineering unit associated with that display value. Alternatively, any number of items can be included on the LCD display. Once the display has been updated, Update_Time is reset and electronic control module  120  moves to block  314  which represents the end of the update display routine. 
     Returning again to block  306 , if the electronic control module  120  determines that Reduced_Complexity is set to On, electronic control module  120  moves to decision block  310 . At decision block  310 , the Display_Value is compared to the sensor value. If the Display_Value equals the sensor value, the display is not updated and electronic control module  120  moves to block  314  which represents the end of the updated display function. However, if the Display_Value is not equal to the sensor value, electronic control module  120  moves to block  312 , where the Display_Value is set to the sensor value. Then, the display is updated with the new Display_Value. However, no other elements on the display are updated. It is possible that the only visible element on the display  110  will be the sensor value itself. Once the LCD display has been updated, Update_Time is reset to zero and the electronic control module  120  moves to block  314  which represents the end of the update display routine. 
     Referring to  FIG. 5B , flow diagram  350  provides a functional description of update display step  208  according to another embodiment of the invention. Electronic control module  120  begins at block  352  and moves to decision block  354 . At decision block  354 , Update_Time is compared to Update_Interval. If Update_Time is not equal to or greater than Update_Interval, electronic control module  120  moves to block  364  which represents the end of the update display routine. 
     Returning again to block  354 , if Update_Time is greater than or equal to Update_Interval, then electronic control module  120  moves to decision block  356 . At block  356 , if Reduced_Complexity is set to Off, electronic control module  120  moves to block  358 . At block  358 , the Display_Value is set to sensor value, the LCD display is updated with the value of Display_Value, as well all other information that might be visible on display  110 . Update_Time is then reset to zero and electronic control module  120  moves to block  364 , the end of step  208 . Returning again to block  356 , if Reduced_Complexity is set to On, electronic control module  120  moves to block  360 . At block  360 , a Display_Value is compared to the sensor value. If the Display_Value is equal to the sensor value, or is within a given tolerance of the sensor value, electronic control module  120  moves to block  364 , the end of step  208 . Tolerance is a value set in the initialized value step  202 . While the Tolerance variable is, in one embodiment, assigned a single, unchanging value, Tolerance can alternatively have a plurality of different values, corresponding to different tolerance values depending upon how far the ambient LCD temperature is below Setpoint — 3. By changing the LCD display value only when the Sensor_Value differs from Display_Value by more than the value of Tolerance, some accuracy may be sacrificed on the LCD  110 . However, the LCD  110  may function at a lower temperature because the display is not updated as often. 
     Returning again to block  360 , if Display_Value differs from Sensor_Value by more than the value assigned to Tolerance, the Display_Value is set to the Sensor_Value and the display value is updated onto LCD  110 . It is to be understood that no other portions of the display which may be visible will be updated. For example, an engineering unit which may normally be displayed will not be updated. Update_Time is then reset and electronic control module  120  moves to block  364  which is the end of the update display function. 
     While the embodiments shown in  FIGS. 5A and 5B  and described above differ in their approach to handling the display when the temperature is below Setpoint — 3, it is to be understood that in an alternate embodiment, an additional Setpoint, having a lower temperature than Setpoint — 3, could be implemented. In such an embodiment, the display may not be updated until the sensor value is different from the Display_Value when the temperature is below Setpoint — 3. When the temperature is below the additional Setpoint however, the Tolerance value is considered and the display value would be updated only when the Display_Value is not within the tolerance level of the sensor value. Such an embodiment would limit the amount of time that a tolerance is considered when comparing the Display_Value and the sensor value, thereby reducing the likelihood that the display value is not exactly what the sensor value is at any given moment. 
     Although the present invention has been described with reference to several alternative embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and the scope of the invention.