Patent Publication Number: US-10317718-B2

Title: Valve positioner

Description:
FIELD OF THE INVENTION 
     The invention relates to valve positioners, and particularly to user interfaces of smart valve positioners. 
     BACKGROUND OF THE INVENTION 
     A control valve is generally used for a continuous control of a liquid or gas flow in different pipelines and processes. In a processing industry, such as pulp and paper, oil refining, petrochemical and chemical industries, different kinds of control valves installed in a plant&#39;s pipe system control material flows in the process. A material flow may contain any fluid material, such as fluids, liquors, liquids, gases and steam. The control valve is usually connected with an actuator, which moves the closing element of the valve to a desired position between fully open and fully closed positions. The actuator may be a pneumatic cylinder-piston device, for example. The actuator, for its part, is usually controlled by a valve positioner, also called as a valve controller, which controls the position of the closing element of the control valve and thus the material flow in the process according to a control signal from the positioner. The positioner is typically controlled with an electrical control signal from a control system (such as by a single twisted pair providing a 4 to 20 mA analog signal) and includes an electric-to-pressure (I/P) conversion to provide a pneumatic control for controlling the actuator. 
     One of the newer devices that offer improved performance of control valves is so-called “smart” positioner or a digital valve controller. A smart positioner is a microprocessor-based electronic positioner with internal logic capability which derives benefit from digital programming to obtain improved positioning performance. An advantage of the smart positioner is that it may be programmed to use a position control algorithm to achieve better dynamic response. Further, the smart positioner may use 2-way communications protocols such Hart, Foundation Fieldbus etc. to communicate with a process control system. This type of communication can be used also to enter new control settings or configurations remotely after installing a smart positioner. 
     However, sometimes there is a need to read measurements, make test runs, or change positioner settings locally at the positioner. Therefore, the smart positioners are often provided with a local user interface (LUI), or a control panel, enabling personnel to, for example, monitor the device behaviour as well as configuring and commissioning the positioning during installation and normal operation. A local user interface may be designed to have, for example, a display to present data and buttons, keypads, switches or other devices to operate the positioner and to enter parameters. For example, the local user interface may comprise a small LCD display and a key-pad with a small number of buttons. Often the display may be viewable through a window in a cover of the housing to allow showing some predetermined information without opening the housing. However, in many existing LUIs it is required that user must open the housing for any kind of operation of the LUI. An example of such approach is the electro-pneumatic positioner PositionMaster EDP300 from ABB Automation Products GmbH. Many oil and gas, petrochemical and process engineering plants are operating in harsh environments which require positioners to function in severe service applications, requiring reliable components with the ability to withstand extreme temperature or ambient fluctuations and have a chemical and corrosion resistance. The positioners must also have a sufficient shock resistance against external mechanical shocks. 
     The opening of the housing is typically cumbersome and time consuming as the cover of the housing is often closed by screws or similar means. The opening of the housing may sometimes be difficult (e.g. due to weather conditions or plant environment) or even impossible (e.g. forbidden by Ex regulations). Every opening of the housing will be a further risk for water ingress. 
     One approach could be to have buttons in the outer surface of the positioner so that they could be operated without opening the housing. For example, Universal positioner SRD960 from Foxboro Eckhardt GmbH has four external mechanical push buttons for local configuration and operation which penetrate the housing of the positioner. The mechanical switches may wear out or they may stuck due to the dirt. While external buttons might provide easy access, there is a new problem related to the security of the LUI usage. The ease of access may call for some protection to be implemented to prevent false input caused by dust, water drops, ice or other environmental sources. A simple keypad lock function may take care of this issue. Furthermore, when the user interface is accessible by not opening the housing, there is always a risk of un-authorized access on purpose or by human mistake. There is a need to prevent unauthorized use of local user interface especially when local user interface is available without opening the positioner cover and it is easy to access the device settings. One approach to solve this is to have PIN code protection to the devices to prevent unauthorized usage. However, it would be frustrating and time consuming to enter a PIN code (i.e. an access code) every time the local user interface is used, especially during start up configuration of the positioner. Further, there can be a high number of positioners and control valves, often hundreds of them, in a single plant, typically from several vendors, so that it would be a challenging task to manage and remember PIN codes for all positioners. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An aspect of the present invention is a local user interface which is easier to access in field conditions while having sufficient access control to maintain security and integrity of the valve control. 
     An aspect of the invention is a smart valve positioner comprising a housing and a housing cover, the housing encompassing control circuitry connectable to a field control line, and a local user interface with one or more buttons and optionally a display for operating the valve positioner, wherein the valve positioner further comprises detector means for detecting whether the housing or the housing cover is open or closed, and the operation mode of the local user interface is configured to be different depending on whether the housing or housing cover is open or closed. 
     In an embodiment, the detector means comprise electrical, optical or mechanical detector means for detecting whether the housing or the housing cover is opened or closed. 
     In an embodiment, the detector means comprise an optical switch, a mechanical switch, a Hall sensor or a Reed switch. 
     In an embodiment, the detector means comprise at least one magnetic element and a sensor arranged detect the presence of the magnetic element, the sensor and the magnetic element being arranged to be close to each other when the housing or housing cover is closed, and to move apart when the housing or the housing cover is opened. 
     In an embodiment, the valve positioner with the housing or the housing cover closed is configured to assume for the local user interface a first user access mode level as a default to thereby allow use of the buttons of the user interface for a first set of user operations, and wherein the valve positioner with the housing or the housing cover opened is configured to assume for the local user interface a further access user access mode level to thereby allow use of the buttons of the local user interface for one or more further sets of user operations. 
     In an embodiment, the valve positioner is configured to assume for the local user inter-face the further user access mode level automatically for a predetermined period of time upon connecting a power to the valve positioner, and wherein the first user access mode level is resumed after expiry of the predetermined period of time from the connection of the power. 
     In an embodiment, the valve positioner is configured to maintain a log on openings of the housing or the housing cover, and/or to record actions made with the housing or the housing cover open, and/or to generate an alarm in response to detecting opening of the housing or housing cover. 
     In an embodiment, the buttons of the local user interface are user-operable from outside the housing without opening the housing or the housing cover. 
     In an embodiment, the local user interface comprises non-mechanical touch buttons enclosed inside the housing, and wherein the touch buttons are user-operable by touching the touch buttons when the housing cover is open, and the housing cover is arranged to make the touch buttons to be user-operable from outside the housing by touching the housing cover, when the housing cover is closed. 
     In an embodiment, the touch buttons comprise optical touch buttons or capacitive touch buttons. 
     In an embodiment, the valve positioner with the housing cover closed is configured to assume for the local user interface a first user access mode level as a default to thereby allow use of the touch buttons through the housing cover for a first set of user operations, and the valve positioner with the housing cover open is configured to assume for the local user interface a further user access mode level to thereby allow use of the non-touch buttons directly on the local user interface for one or more further sets of user operations. 
     In an embodiment, said first set of user operations include reading operations, and said one or more further sets of user operations include reading operations and procedures for locally controlling parameters and operation of the smart valve positioner. 
     A further aspect of the invention is a valve assembly comprising a valve, an actuator, and a valve positioner according any one or any of combination of its embodiments. 
     A still further aspect of the invention is use of a smart valve positioner according any one or any of combination of its embodiments in a process industry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described by means of exemplary embodiments with reference to the attached drawings, in which 
         FIG. 1  illustrates a schematic block diagram of an exemplary process automation system; 
         FIG. 2  illustrates an exemplary arrangement wherein a pneumatic actuator operates the process valve under control of the valve positioner; and 
         FIG. 3  shows a schematic block diagram of an exemplary intelligent valve controller wherein a fluid valve assembly according to embodiments of the invention may be applied; 
         FIG. 4  illustrates an exemplary local user interface of a smart valve positioner comprising a local user interface panel within housing and a housing cover allowing use of touch buttons through the cover; 
         FIG. 5A  illustrates a top view of an exemplary positioner with a housing cover placed on the local user interface panel (housing closed); 
         FIG. 5B  illustrates a top view of the exemplary housing cover when removed from the local user interface panel (housing opened); 
         FIG. 5C  illustrates a top view of an exemplary local user interface panel when the housing cover is removed (housing opened); 
         FIGS. 6A and 6B  show a top view and a cross-sectional view, respectively of an exemplary capacitive touch button when the housing cover is open; 
         FIG. 6C  shows a cross-sectional view of the exemplary capacitive touch button when the housing cover is closed; 
         FIG. 7  shows a schematic block diagram for an exemplary local user interface connected to a microcontroller; 
         FIGS. 8A and 8B  show a top view and a cross-sectional view, respectively of an exemplary optical touch button when the housing cover is open; and 
         FIG. 8C  shows a cross-sectional view of the exemplary optical touch button when the housing cover is closed. 
     
    
    
     EXAMPLE EMBODIMENTS OF THE INVENTION 
     The invention relates to valve positioners, and particularly to user interfaces of smart valve positioners. 
       FIG. 1  shows a schematic block diaphragm of an exemplary process automation system wherein the principles of the invention may be applied in a valve positioner. The control system block  5  generally represents any and all control room computer(s)/programs and process control computer(s)/programs as well as databases, which may be interconnected by a factory LAN  4 , in the automation system. There are various architectures for a control system. For example, the control system may be a Direct Digital Control (DDC) system or Distributed Control System (DCS), both well known in the art. It should be appreciated that the type or architecture of the automation system is not relevant to the present invention 
     In the example of  FIG. 1 , a control valve assembly comprising a process valve  1  and a positioner  2  and an actuator  3  may be connected to a process to control the flow of a substance in process pipeline  7 . Material flows of a process or process pipeline may be controlled in a processing industry, such as pulp and paper, oil refining, petrochemical and chemical industries. The material flow may contain any fluid material, such as fluids, liquors, liquids, gases and steam. Although only one controlled process valve assembly is shown in  FIG. 1 , an automation system may, however, include any number of field devices, such as control valve assemblies, often hundreds of them.  FIG. 2  illustrates a mechanical structure of an exemplary control valve assembly wherein a pneumatic actuator  3  operates the process valve  1  under control of the valve positioner  2 . An example of a process valve  1  is Neles® RotaryGlobe control valve from Metso Corp. An example of a valve positioner  2  wherein embodiments of the invention may be applied is Neles® ND9000 intelligent valve controller from Metso Corp. An example of an actuator  3  is Quadra-Power X series pneumatic actuator from Metso Corp. However, it is to be understood that, beyond a local user interface of the positioner  2 , the type and implementation of the control valve assembly is not relevant to the present invention. As used herein, “control valve” means also an on/off type shutoff valve. 
     There are various alternative ways to arrange the interconnection between the control system and field devices, such as control valves, in a plant area. In  FIG. 1 , the field/process bus  6  generally represents any such interconnection. Traditionally, field devices have been connected to the control system by two-wire twisted pair loops, each device being connected to the control system by a single twisted pair providing a 4 to 20 mA analog input signal. More recently, new solutions, such as Highway Addressable Remote Transducer (HART) protocol, that allow the transmission of digital data together with the conventional 4 to 20 mA analog signal in the twisted pair loop have been used in the control systems. The HART protocol is described in greater detail for example in the publication HART Field Communication Protocol: An Introduction for Users and Manufacturers, HART Communication Foundation, 1995. The HART protocol has also been developed into an industrial standard. Examples of other fieldbuses include Foundation Fieldbus and Profibus PA. However, it is to be understood that the type or implementation of the field/process bus  3  is not relevant to the present invention. The field/process bus  3  may be based on any one of the alternatives described above, or on any combination of the same, or on any other implementation. 
     The operation of an intelligent (smart) valve positioner, such as the positioner  2 , may be based on a microcontroller, such as a microprocessor (μP), which controls the position of the valve  1  on the basis of control information obtained from the field connection line or fieldbus  6 . The positioner is preferably provided with valve position measurement, in addition to which it may be possible to measure many other variables, such as supply pressure for pressurized air, pressure difference over actuator piston or temperature, which may be necessary in the self-diagnostics of the valve or which the valve controller transmits as such or as processed diagnostic information to the control room computer, process controller, condition monitoring computer or a similar higher-level unit of the automation system via a field bus. 
     An example block diagram of microcontroller-based smart valve positioner, such as positioner  2 , is illustrated in  FIG. 3 . The exemplary positioner  2  may include a microcontroller unit  21  having an electrical control output  26 , and a pneumatic unit  23 ,  25  that takes in the electrical control signal  26  and converts it to a corresponding fluid pressure output P 1 , P 2  at actuator ports C 1 , C 2  connected to an actuator  3 . The pneumatic unit may comprise a prestage  23  and an output stage  25 . The prestage  23  may perform an electric-to-pressure (I/P) conversion of the electrical control signal  26  into a small pilot pneumatic control signal  24  which is sufficient to control the output stage  25 . The supply port S of the output stage  25  may be connected to a supply air pressure S. The output stage  25  may amplify the small pneumatic pilot signal into a larger pneumatic pressure output signals  33   34  at the actuator ports C 1 ,C 2  to move a diaphragm piston  32  of the actuator  3 . A position sensor  22  may be provided to measure the position of the actuator or valve for the microcontroller  21 . For example, the sensor  22  may be arranged to measure the rotation of a feedback shaft  31  of an actuator. A microcontroller unit  21  controls the valve position according to a control algorithm run in the microcontroller  21 . To that end, the microcontroller  21  may receive an input signal (a set point) over a process/fieldbus  7 , such as 4-20 mA pair and HART, which is connected to a connector  27 . The positioner  2  may be powered from a 4-20 mA loop or fieldbus. The microcontroller  21  may also read one or more of a supply pressure sensor Ps, a first actuator pressure sensor P 1 , a second actuator pressure sensor P 2 , and an output stage position sensor SPS. The positioner  2  may further contain a Local User Interface (LUI)  20  connected to the microcontroller  21 . The microcontroller  21  may display any information on a display of the local user interface  20 , and receive commands and parameters from a keypad or buttons of the local user interface  20 . It should be appreciated that the illustrated valve positioner is merely an example and the type or implementation of a valve positioner  2 , beyond a local user interface, is not relevant to the present invention. 
     The local User Interface (LUI) functions may include, for example, one or more of the following functions: Local control of the valve; Monitoring of valve position, target position, input signal, temperature, supply and actuator pressure difference; Guided-startup function; LUI  20  may be locked remotely to prevent unauthorised access; Calibration, e.g. an automatic or manual linearization; 1-point calibration; Control configuration: aggressive, fast, optimum, stable, maximum stability; HART/Fieldbus version configuration; Configuration of the control valve; Rotation: valve rotation clockwise or counter-clockwise to close; Dead Angle; Low cut-off, cut-off safety range; Positioner fail action, open/close; Signal direction: Direct/reverse acting; Actuator type, double/single acting; Valve type, rotary/linear; Language selection. 
     An aspect of the invention is a local user interface (LUI) of a smart positioner which is easier to access in field conditions while having sufficient access control to maintain security and integrity of the valve control. 
     An aspect of the invention is a smart valve positioner  2  comprising a housing  200  and a housing cover  202 , such as an exemplary positioner  2  in  FIG. 4 . The housing  200  may encompass the control circuitry, such as circuitry  212  (e.g. on a system printed circuit board) connectable to a field control line, and a local user interface unit (e.g. on a LUI printed circuit board), such as the panel  201 , with one or more touch buttons  204 - 1  . . .  204 -N and a display  203  for monitoring and configuring the positioner during installation and normal operation the valve positioner  2 . The local user interface panel  201  is enclosed inside the housing  200  by the housing cover, such as a cover  202 , when the housing  200  is closed. The housing cover  202  may be transparent or comprise a transparent window  213  so that the display  203  may be viewable through the housing cover  202  without opening the housing.  FIG. 5A  illustrates a top view of an exemplary positioner  2  with the housing cover  202  placed on top of the local user interface panel  201  (housing closed),  FIG. 5B  illustrates a top view of the exemplary housing cover  202  when removed from the top of the local user interface panel  201  (housing opened), and  FIG. 5C  illustrates a top view of an exemplary local user interface panel  201  when the housing cover  202  is removed (housing opened). 
     According to an aspect of the invention the local user interface panel  201  may comprise touch buttons, such as touch buttons  204 - 1  . . .  204 -N, and the housing cover  202  may be arranged to make the touch buttons of the local user interface panel  201  user-operable by touching the outer surface of the closed housing cover  202  without contacting the actual touch buttons  204 - 1  . . .  204 -N under the housing cover  202 . The outer surface of the housing cover  202  may be provided with appropriate markings to assist the use of the buttons  204 - 1  . . .  204 -N, as illustrated in  FIGS. 5A and 5B . The markings may be printed or otherwise produced to the housing cover  202 . Embodiments of the invention employ the touch button technology in a special manner so that user can access the local user interface without opening the positioner housing. In embodiments, the touch buttons  204 - 1  . . .  204 -N may be arranged to detect an electrical or optical influence of a user finger in the close proximity, and the housing cover  202  may adapted to enable such electrical or optical influence through the housing cover  202  to the touch button when the user finger touches a predetermined point on the outer surface of the housing cover  202 . In embodiments, the thickness of the housing cover  202  may be reduced at locations of the buttons in comparison with the overall thickness of the housing cover, in order to facilitate the touch detection. For example, there may be recession  202 A on the outer surface of the housing cover  202  at location of each button as illustrated by a broken line in  FIG. 4 . For example, the housing cover  202  may be made of glass or thermoplastic polymer, such as polycarbonate. The cover material may be electrical insulator if capacitive touch button technology is utilized for buttons  204 - 1  . . .  204 -N. In case of optical touch button technology, the electrical conductivity of the cover  202  is not relevant. In exemplary embodiments, capacitive or optical, i.e. non-mechanical, buttons may be used for the touch buttons of the local user interface panel. The invention is, however, not intended to be limited to any specific keypad technology but any technology may be employed that allow operating the buttons or keypad with the housing cover  202  closed. 
     One requirement for a valve positioner may be a sufficient shock resistance against external mechanical shocks. In an embodiment, there may an air gap or space, such as the gap  211  illustrated in  FIG. 4 , between the inner surface of the housing cover  202  and the outer surface of the local user interface panel  201 . Alternatively, there may be one or more shock-absorbing intermediate layers between the inner surface of the housing cover  202  and the outer surface of the local user interface panel  201 , instead of the gap  211 . Thereby, the cover  202  may not directly mechanically contact the local user interface panel, and a bending or other deformation of the cover due to external factors, such as external shocks, may be allowed in some degree without exerting excessive forces to the local user interface panel  201  and causing damage to it. 
     An air gap or a shock absorbing layer  211  may reduce the detectable electrical or optical influence through the housing cover  202  to the touch button when the user finger touches a predetermined point on the outer surface of the housing cover  202 . In an embodiment, in order to compensate such effect, a suitable elastic contact pad, such as a contact gel pads  206 , may be locally arranged between each of the touch buttons  204  and  205  and the housing cover  202 . In an embodiment, such contact pads  206  may be attached to corresponding points on the internal surface of the housing cover  202 . Examples of materials and structures for the contact pads include conductive foam pads cut to dimension, conductive EMC gaskets and other electrically conductive flexible materials, such as a compressed spring. These conductive pads may be glued or attached permanently by other means to housing cover or the LUI cover. Such pads may also be produced by injection molding of conductive flexible material on the locations of buttons to device cover or LUI cover. In embodiments using optical touch buttons, the air gap  211  may not affect the touch detection through the housing cover  202  and no contact pads may be needed. However, in order to assure a proper optical path between the optical touch button and the housing cover  202 , contact pad or element  206  with suitable optical properties may be used. 
     In embodiments of the invention, the buttons of the local user interface panel  201  may be capacitive touch buttons. The capacitive-touch mechanism is schematically illustrated by a design example in  FIGS. 6A and 6B .  FIGS. 6A and 6B  show a top view and a cross-sectional view, respectively of an exemplary capacitive touch button  204  implemented on a printed circuit board (PCB)  61 . The exemplary capacitive touch button  204  may comprises and a nonconductive overlay material  62 , a conductive sensor pad or trace  63  surrounded by a grounded conductive plane or trace  64  on the to surface of the PCB  61 , and an insulated (non-conductive) overlay  62  placed directly over them to protect them from the environment and prevent direct finger contact. The overlay material  62  is placed over the sensor pad to protect it from the environment and prevent direct finger contact. The sensor pad and the grounded hatch may be separated by an intermediate uniform gap  65 . The ground plane  64  also helps to shield the capacitive button structure from possible other electronics. The sensor pad  63 , the grounded plane  64  and the gap  65  can be made with conventional printed circuit techniques to be part of the PCB  61 . In the example of  FIG. 6B , a two-layer printed circuit board is used with sensor pads  63  and a ground plane  64  on the top, and a connection wiring or traces  67  and possible associated electrical components (not shown) on the bottom. Examples of such electrical components include a capacitance-measuring circuitry, such a touch controller and associated parts that convert a sensor capacitance into digital format. A conductor via or through hole  66  in the PCB  61  may connect each sensor pad  63  to the respective trace  67  on the bottom side of the board  61 , as illustrated in  FIG. 6B . In the example illustrated in  FIG. 6A , there is a round sensor pad  63  and an annular gap  65 , but a sensor pad or trace may assume any shapes. In  FIGS. 6A and 6B  only one button  204  is illustrated but there may be any number of buttons in the same panel or PCB. For example, a LUI  20  with N touch buttons  204 - 1 ,  204 - 2 ,  204 - 3 , . . . ,  204 -N on the same panel is schematically illustrated in  FIG. 7 . The exact implementation of the touch button is not relevant with respect to the present invention. 
     As illustrated in  FIGS. 6A and 6B , a capacitive touch button  204  is essentially a capacitor formed from two adjacent traces  63  and  64 , and the laws of physics determine how much capacitance exists between them. Dashed lines  68  represent an electric field between the sense pad  63  and the grounded plane  64 . If a finger is brought in close proximity to the capacitive button  204 , the finger disrupts the electric field  68 , which sees the finger as a conductive foreign object, thus changing the capacitance. Place a finger on the overlay  62 , and the capacitance increases. Remove the finger, and the capacitance decreases. By measuring the capacitance, the presence or absence of a finger can be determined. 
     Several commercial solutions for capacitive touch sensing are available, for example in form of dedicated function integrated circuits, and in form of software libraries for microcontrollers having built-in sensor interface electronics like, for example, analog to digital converters and analog comparators. The exact implementation of the touch sensor signal processing is not relevant with respect to the present invention. 
       FIG. 7  shows a schematic block diagram for an exemplary local user interface  20  connected to a microcontroller  21 . The LUI  20  may contain a display  203  controlled by the microcontroller  203 , and a capacitive touch pad with N capacitive touch buttons  204 - 1 ,  204 - 2 ,  204 - 3 , . . . ,  204 -N. Each capacitive touch button  204 - 1 ,  204 - 2 ,  204 - 3 , . . . ,  204 -N may be implemented with a structure shown in  FIG. 6B , resulting in a N sensor pads  63  surrounded by a common ground plate  64 . Each sensor pad  63  may be connected with a respective wire  67  to a sensor input of a touch controller  71 . An example of a commercial circuit suitable for the touch controller  71  is LDS6100/6120 family of capacitance touch controllers from Integrated Device Technology Inc. When configured for capacitive sensing, the touch inputs are directed to the touch controller  71  which senses changes in the external sensor pads  63 . When a change in capacitance occurs above a user defined threshold, a touch event is recognized and the host processor  21  is notified. Capacitive sensing may be accomplished using a sigma-delta converter capable of converting a sensor input signal into a digital output that may be compared against a touch/no-touch threshold value to determine if a touch has occurred. The button status and digitized capacitance values may be stored in on-chip registers available to the host processor  21 . 
     As discussed above,  FIG. 6B  shows a cross-sectional view of an exemplary capacitive touch button  204  as normally used, i.e. the overlay  62  forms the touch surface. In embodiments of the invention this is the situation wherein the housing cover is opened and the touch button  204  is exposed to be operated directly by touching the overlay  62 .  FIG. 6C  shows a cross-sectional view of the exemplary capacitive touch button  204  when the housing cover  202  is closed, i.e. placed on top of the touch button  204 . In  FIGS. 6A, 6B and 6C  same reference symbols represent the same or equivalent structures or functions. The material of the housing cover is an electrical insulator (non-conductive). Conductive material cannot be used in the housing cover  202  because it interferes with the electric field pattern  68 . One requirement for a valve positioner may be a sufficient shock resistance against external mechanical shocks. As discussed above, there may be an air gap or space  211  between the housing cover  202  and the overlay  62  of the touch button  204  in order to improve the resistance to external shock, such as the gap  211  illustrated in  FIG. 4 , between the inner surface of the housing cover  202  and the outer surface of the local user interface panel  201 . Because air has a relatively low dielectric constant which reduces the sensitivity, any air gap between the housing cover  202  and overlay  62  is preferably eliminated at least at the location of the sensor pad  63 . To that end, as has been discusses above, a suitable elastic contact pad  206  may be locally arranged between the touch buttons  204  and the housing cover  202  to couple the electric field  68  from the overlay  62  to the housing cover  202 . The housing cover  202  further reduces the electric field  68  reaching the top surface of the housing cover. However, the inventors have observed that, in spite of these additional layers and materials which reduce the sensitivity of the underlying touch button  204 , the capacitance measurement can still be adjusted to detect a finger touching the top surface of the housing cover  202 . Thus, the local user interface  20  located under the housing cover can be operated also when the housing cover is closed. In embodiments, when a thick cover is required to obtain sufficient mechanical robustness, the thickness of the housing cover  202  may be reduced at locations of the buttons in comparison with the overall thickness of the housing cover, in order to facilitate the touch detection, as illustrated in  FIG. 4 . The same measurement circuitry, such as that illustrated in  FIG. 7 , can be used for detecting a touch event with the cover closed and open. 
     In embodiments of the invention, the buttons of the local user interface panel  201  may be optical touch buttons. A reflective optical touch sensing mechanism is schematically illustrated by an example in  FIGS. 8A, 8B and 8C .  FIGS. 8A and 8B  show a top view and a cross-sectional view, respectively of an exemplary optical touch button  204  implemented on a printed circuit board (PCB)  81 . The exemplary optical touch button  204  may comprise an optical sensor  82  having a light emitter or transmitter (Tx)  84  and a light detector or receiver (Rx)  85 , and a transparent overlay material  82  placed on the top of the sensor to form a touch surface with a window. The overlay  82  is typically very thin, or sometimes omitted. The optical sensor  83  may operate with infrared light, for example. The emitter  84  of optical sensor  83  may be implemented by a LED, and the detector  85  may be implemented by a photodiode, for example. Alternatively, phototransistors or other types of light emitter and light detector devices may be used. Examples of commercial optical sensors include OPB744 from OPTEK Technology Inc., and HSDL-9100 from Avago Technologies. The emitter may emit IR light pulses  88 . This light travels out in the field of view and will either hit an object or continue. No light will be reflected when no object (such as a finger) is detected. On the other hand, if an object is present on the propagation path of light  88 , IR light will reflected from the object and detected by the detector  84 . The output of the detector  84  may itself be a touch status signal that indicates a touch event if the reflected light level exceeds a predetermined threshold. Alternatively, the detector  84  may have an associated circuitry (such as a comparator) that provides the touch status signal based on the output signal of the detector  84 . Still alternatively, the micro controller  21  of the positioner may make a decision on a touch event based on the output signal level of the detector  84 , for example. The touch status signal from detector  84  or the associated circuitry may be applied to the micro controller  21  of the positioner. The associated circuitry may be similar to the touch controller  71  illustrated for a capacitive touch button in  FIG. 7 . Also otherwise the circuit arrangement may be similar to that illustrated in  FIG. 7 , except that optical touch buttons and optical touch controller are employed. Further, in  FIGS. 8A and 8B  only one button  204  is illustrated but there may be any number of buttons in the same panel or PCB. For example, the N touch buttons  204 - 1 ,  204 - 2 ,  204 - 3 , . . . ,  204 -N illustrated in  FIG. 7  may be implemented with N optical touch buttons. However, the exact implementation of the touch button or detection of the touch event is not relevant with respect to the present invention. 
     As discussed above,  FIG. 8B  shows a cross-sectional view of an exemplary optical touch button  204  as normally used, i.e. the overlay  82  forms the touch surface. In embodiments of the invention this is the situation wherein the housing cover is opened and the touch button  204  is exposed to be operated directly by touching the overlay  82 .  FIG. 8C  shows a cross-sectional view of the exemplary capacitive touch button  204  when the housing cover  202  is closed, i.e. placed on top of the touch button  204 . In  FIGS. 8A, 8B and 8C  same reference symbols represent the same or equivalent structures or functions. The material of the housing cover can be anything that allows providing an optical path for the light to and from the optical sensor  83 . The housing cover  202  further reduces the level of light reflected from the object touching the top surface of the housing cover. If required, the longer distance to the object may be compensated by increasing the emission power of the emitter  83  and/or the sensitivity (threshold) of the detector  84 . Thus, a finger touching the top surface of the housing cover  202  can be detected, and thereby the local user interface  20  located under the housing cover can be operated also when the housing cover is closed. In embodiments, when a thick cover is required to obtain sufficient mechanical robustness, the thickness of the housing cover  202  may be reduced at locations of the buttons in comparison with the overall thickness of the housing cover, in order to facilitate the touch detection, as illustrated in  FIG. 4 . The same measurement circuitry, such as circuitry similar to that illustrated in  FIG. 7 , can be used for detecting a touch event with the cover closed and open. 
     One requirement for a valve positioner may be a sufficient shock resistance against external mechanical shocks. As discussed above, there may be an air gap or space  211  between the housing cover  202  and the overlay  82  of the touch button  204  in order to improve the resistance to external shocks. The air gap does not interfere with the optical signal but the longer distance and the bottom of the housing cover may increase cross-talk from the emitter  83  to the detector  84 . Therefore, an element reducing the cross talk may be provided between the housing cover  202  and the optical touch button  204 . Such element may be any structure separating the paths of the emitted light and the reflected light in the air gap. The element may be a simple separating wall or baffle, for example. In an embodiment two separated light guides may be used. 
     The local user interface according to embodiments of the invention improves both the reliability and the usability of the user interface. As the touch buttons of the local user interface  20  located inside the positioner housing can be operated by touching the housing cover, the local user interface is totally sealed from the environment and protected from external forces. The touch buttons do not penetrate the housing cover of the positioner. There are no mechanical forces exerted directly on the buttons. The touch buttons do not wear out. All external stress is received by the housing cover. This can make the local interface of the positioner more reliable. Mechanical switches wear out and also must penetrate the positioner housing. A touch panel provided on the outer surface of the positioner would be exposed to the environment and the external mechanical forces. On the other hand, a normal touch panel which is under a cover and can be operated only with cover open is more cumbersome to use. However, the user interface being accessible without opening the positioner housing, there is always a risk of un-authorized access on purpose or by human mistake. Further, the ease of access to operate a local user interface  20  will call for some protection to be implemented to prevent false input caused by dust, water drops, ice or other environmental sources, or by human errors. 
     An aspect of the invention is a protection against un-authorized access and simultaneously against false inputs due to human errors or environmental reasons in such a positioner in which the local user interface can be operated without opening the positioner housing. 
     It should be appreciated that principles of this aspect of the invention are applicable not only to the local user interface according to embodiments of the first aspect of the invention but also to other types of local user interfaces. With respect to the second aspect of the invention, the implementation or design of the local user interface is not relevant beyond that the access rights are different depending on whether the housing of the positioner is opened or closed. In this context, the opening of housing refers to any type of accessing connectors or other components within the housing of the positioner. 
     According to an aspect of the invention the valve positioner is configured to change an operation mode of the local user interface, when the housing or housing cover is opened. The change in the operation mode may appear to a user as different menus, different prompts, different control views, different operations, etc. which are not presented and/or accessible when the housing or housing cover is closed. 
     According to an aspect of the invention the local user interface may have a first user access mode level allowing use of the buttons of the local user interface for a first set of user operations and one or more further user access mode levels allowing use of the buttons of the local user interface  20  for one or more further sets of user operations. In other words, different levels of access rights may be defined for a LUI operation. The local user interface may assume a specific level of access rights when predetermined conditions are fulfilled. 
     In an embodiment the local user interface may assume different levels of access rights depending on whether the housing or enclosure of the positioner is open or closed, e.g. whether a cover of the housing is open or closed. In other words, an automatic access right control may be implemented by detecting the open/close state the housing. This requires that the state of the housing cover is known. The risk of altering valve package or process critical parameters by mistake is highly reduced. Installation related parameter access may be granted only when the valve positioner is in an installation phase (i.e. the housing is open, e.g. due to the cover being open). A separate keypad lock function is not necessarily required to prevent false input caused by dust, water drops, ice or other environmental sources, because the altering of parameters may be prevented when the housing, e.g. a housing cover, is closed. However, a keypad lock function may still be implemented as a redundant safety feature. 
     In an embodiment the positioner  2  may be provided with electrical, optical or mechanical detector means for detecting whether the housing, is opened or closed. In an embodiment the detector means are arranged to detect whether a housing cover is open or closed. In an embodiment the removable part of the positioner, such as the housing cover  202 , may comprise at least one magnetic element and the other part of the positioner, such as the local user interface panel  201 , the housing  200  or any other component within the housing, may be provided with at least one sensor or detector arranged detect the presence or proximity of the magnetic element. The output of these devices switches low (turns on) when a magnetic field from the magnetic element exceeds a threshold (the cover is closed). When the magnetic element is moved away (the cover is opened), magnetic field is reduced below a release threshold and the device output goes high (turns off). Examples of suitable detectors or sensors include a Hall sensor and a Reed switch. An example of a commercial Hall sensor is A1210 from Allegro MicroSystems, LLC. 
     In an exemplary embodiment illustrated in  FIG. 4  the cover state detection can be achieved by having a permanent magnet  208  on the housing cover  202  and a detector, such as Hall sensor or Reed switch,  207  on the local user interface panel  201  (e.g. on a LUI printed circuit board) or on a system printed circuit board  212 , for example, to detect the presence of the magnet  208 . If necessary, one or more additional pairs of a small permanent magnet  210  and a detector or sensor  209  may be used for robustness or to improve the immunity against strong external magnetic fields or magnetic jamming. 
     Examples of optical and mechanical detectors for detecting the opening state of the housing include an optical switch (e.g. a phototransistor) or a mechanical micro switch, for example. An optical or mechanical switch may be used especially if immunity against strong external magnetic fields or magnetic jamming is required. An optical switch pair or mechanical switch pair may also be duplicated (in a similar manner as the magnet/Hall-switch pairs in  FIG. 4 ). 
     In an embodiment, the detector  207 / 209  for detecting the opening state of the housing, e.g the state of the cover  202 , may provide the state information in form of a two-state digital signal (OPEN/CLOSE) which makes it robust against electrical noise. 
     In an embodiment the r opening state information may be provided from the detector to a control unit or a microcontroller, such as from the detector(s)  207 / 209  to the microcontroller  21  as illustrated in  FIG. 7 . The control unit or microcontroller  21  may utilize the opening state information in the system level to access control or to define access profile to the local user interface  20 . 
     In an embodiment, when the housing of the positioner is closed, the local user interface  20  may be configured to assume the first user access mode level as a default to thereby allow use of the buttons of the LUI  20  for the first set of user operations. In an exemplary embodiment, the touch buttons  204 - 1  . . .  204 -N may be used through the housing cover  202 . When the housing is open, the local user interface  20  may be configured to assume a further access user access mode level to thereby allow use of the buttons of the LUI  2020  for one or more further sets of user operations. In an exemplary embodiment, the touch buttons  204 - 1  . . .  204 -N may be used directly on the local user interface panel  201 . 
     In an embodiment, when the housing of the positioner is closed, the local user interface  20  may be configured to assume the first user access mode level as a default to thereby allow use of the buttons of the LUI  20  for reading operations. In an exemplary embodiment, the touch buttons  204 - 1  . . .  204 -N may be used through the housing cover  202  for reading operations. When the housing is open, the local user interface  20  may be configured to assume a further access user access mode level to thereby allow use of the buttons of the LUI  20  for reading operations and procedures for locally configuring parameters and controlling operation of the smart valve positioner. In an exemplary embodiment, the touch buttons  204 - 1  . . .  204 -N may be used directly on the local user interface panel  201  for reading operations and procedures for locally configuring parameters and controlling operation of the smart valve positioner. Examples of configuration parameters may include valve type, actuator type, positioner fail action, valve rotation direction, and valve dead angle. 
     In an embodiment, when the housing of the valve positioner  2  is closed, the local user interface  20  is configured to require a dedicated access code for at least one further user access mode levels to thereby allow use of the buttons of the LUI  20  one or more further sets of user operations, e.g. for reading operations and for locally controlling parameters and operation of the smart valve positioner. In an exemplary embodiment, the touch buttons  2041  . . .  204 -N may be used through the closed housing cover  202  for one or more of the further sets of user operations, e.g. for reading operations and for locally controlling parameters and operation of the smart valve positioner. 
     An example of user access rights based on the housing opening state is illustrated below. 
     State 1: Housing closed
         User may browse through parameter set A   User may access diagnostics graphs   User may not change parameters   User may not start tests       

     State 2: Housing open
         User may browse through parameter set A   User may browse through parameter set B   User may access diagnostics graphs   User may change parameters   User may start tests       

     In an embodiment, an alarm may be initiated when an opening of the positioner housing is detected. In an embodiment, a log may be maintained on the openings of the housing. In an embodiment, all actions made with the housing open may be recorded. 
     As noted above, different levels of access rights may be defined for a LUI operation. The local user interface may assume a specific level of access rights when predetermined conditions are fulfilled. In embodiments, the predetermined conditions for assuming different levels of access rights may comprise different access codes, i.e. PIN codes, for different levels of access rights to the local user interface. This may alleviate the problem normally related to the use PIN code protection: it is very frustrating and cumbersome to enter PIN code every time a local user interface is used. This is especially true for a (OEM) valve vendor at setup phase during configuration and assembly of the valve. An example of associating several levels of LUI access rights to different PIN codes may be as follows: 
     Level 1. Everyone should have readers access, all parameters, measurements and alarms. They are readable without entering a PIN code. 
     Level 2. A PIN code (that optionally can be disabled) would be required to enter typical valve assembly related parameters and to run calibration and device tests. 
     Level 3. Third level users would have an extended view to the device settings and more advanced parameters. Extended menu would appear when entering a specific PIN code. The extended menu would contain rarely used user parameters to make a more complicated device parameterization (examples could be control algorithm related parameters that should not be set in normal cases, or rarely used signal modification parameters). 
     Level 4. Fourth level could be for specialist of the vendor (e.g. Metso) to have access to all device parameters to be used in trouble shooting, problem mitigation or extreme cases, for example. 
     In an embodiment, a higher level of access rights may be activated automatically for a predetermined period of time upon connecting a power to the positioner  2 , e.g. upon connecting the fieldbus wires or the 4-20 mA twisted pair loop  7  to the connector of the positioner  2 , such the connector  27  in  FIG. 3 . During the predetermined period of time, such as approximately one hour, a predetermined extended access to the local user interface may be allowed without requiring PIN codes. The requirement to use normal level PIN codes to enter higher levels of access rights may be resumed after expiry of the predetermined period of time from the connection of the power is connected to the device. This would make sure that during the valve assembly it is easy to set up the right parameters in the positioner without need to all the time enter PIN codes. In normal site conditions during the operation, where parameter settings are not that frequent, the positioner would be protected from unauthorized usage by the PIN codes. 
     In an embodiment, if each user or user group has a unique PIN code, a log may be maintained on who has logged in the local user interface of the positioner and what actions have been done. Whenever user logs in to the local user interface, there will be an event in an event log. In an embodiment, users, access rights and PIN codes may be managed in a valve management system (such as the Metso Valve Manager, DTM), and list of users with PIN codes may be sent to each positioner  2  over the field bus  7 . 
     The description and the related figures are only intended to illustrate the principles of the present invention by means of examples. Various alternative embodiments, variations and changes are obvious to a person skilled in the art on the basis of this description. The present invention is not intended to be limited to the examples described herein but the invention may vary within the scope and spirit of the appended claims