Abstract:
A method is disclosed for determining leakby in a flow controller ( 100 ) comprising a flow sensor ( 102 ), a flow control valve ( 106 ) and electronics ( 104 ). The electronics are coupled to the flow sensor, the flow control valve and configured to adjust the flow control valve in response to the signal of the flow sensor indicating the flow rate of the material such that a set flow rate of material through the flow controller is maintained. The steps of the method comprise determining ( 302 ) a zero drift (Qdrift) value for the flow sensor ( 102 ). Determining ( 304 ) a flow rate (Qflow) through the flow controller ( 100 ) when the control valve ( 106 ) is in the fully closed position. And determining ( 306 ) the leakby through the flow controller ( 100 ) where the leakby is equal Qflow-Qdrift.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Flow controllers are typically used to control the flow rate of a fluid in a process. Flow controllers are typically comprised of a flow sensor, a flow control valve and electronics (with optional software) to control the valve in response to the flow rate detected by the flow sensor. The flow sensor may be a thermal mass flow sensor, a Coriolis mass flow sensor, a positive displacement flow meter, or the like. Some flow controllers use valves that may not completely stop the flow of fluid when the valve is in the fully closed position. These types of flow controllers have a specified amount of fluid which may leak through the controller when the flow control valve is in the “off” or fully closed position. The amount of fluid leaking through the valve under these conditions is called leakby and is defined as the amount of fluid leaking through the flow controller when the controller is in the “off” or fully closed position. Manufacturers that use flow controllers may tune their process around this leakby specification. If the flow controller degrades or fails and the leakby value increases above the specification, manufactures may incur significant production scrap. Testing a flow controller for leakby currently requires removing or isolating the device from the process equipment and measuring the leakby value using an off-line piece of measurement equipment. Shutting down the process equipment to isolate the flow controller and attach the off-line measuring equipment may cause considerable downtime for the process equipment. In capital intensive facilities such as semiconductor factories, downtime can be very expensive. 
       ASPECTS 
       [0002]    One aspect of the invention includes a method for determining leakby in a flow controller ( 100 ), comprising: 
         [0003]    determining a zero drift (Qdrift) value for the flow controller ( 100 ); 
         [0004]    determining a flow rate (Qflow) through the flow controller ( 100 ) when the flow controller ( 100 ) is in the fully closed position; 
         [0005]    determining the leakby through the flow controller ( 100 ) where the leakby is equal to Qflow-Qdrift. 
         [0006]    Preferably, the method further comprises: 
         [0007]    stopping flow through the flow controller ( 100 ) using a fluid device; 
         [0008]    determining the indicated flow rate through an internal flow sensor ( 102 ); 
         [0009]    comparing the indicated flow rate with a previously stored flow rate to determine the zero drift (Qdrift) value. 
         [0010]    Preferably, the method further comprises the fluid device is selected from the following group: a single external valve, a first external valve located on an inlet side of the flow controller and a second external valve located on an outlet side of the flow controller, a single integrated valve, a first integrated valve located on an inlet side of the flow controller and a second integrated valve located on an outlet side of the flow controller, a pump, a pressure release valve. 
         [0011]    Preferably, the method further comprises the fluid device is manually controlled. 
         [0012]    Preferably, the method further comprises the fluid device is electrically controlled. 
         [0013]    Preferably, the method further comprises: 
         [0014]    waiting a preset time before determining the indicated flow rate through the internal flow sensor ( 102 ). 
         [0015]    Preferably, the method further comprises determining a flow rate (Qflow) through the flow controller ( 100 ) further comprises: 
         [0016]    allowing flow through the flow controller ( 100 ); 
         [0017]    setting the flow controller ( 100 ) to the fully closed position; 
         [0018]    determining an indicated flow rate through an internal flow sensor ( 102 ) and equating the indicated flow rate to the flow rate (Qflow) through the flow controller ( 100 ). 
         [0019]    Preferably, the method further comprises: 
         [0020]    attaching an external device ( 110 ) to the flow controller ( 100 ) and operating the flow controller ( 100 ) using the external device ( 110 ) to determine the leakby. 
         [0021]    Preferably, the method further comprises: 
         [0022]    comparing the leakby with a threshold value; 
         [0023]    when the leakby is greater than the threshold value establishing an error condition. 
         [0024]    Another aspect of the invention comprises a flow controller, comprising: 
         [0025]    a flow sensor that generates a signal indicating the flow rate of a material flowing through the flow controller; 
         [0026]    a flow control valve; 
         [0027]    a display; 
         [0028]    an input device; 
         [0029]    electronics coupled to the flow sensor, the flow control valve, the display and the input device and configured to adjust the flow control valve in response to the signal indicating the flow rate of the material such that a set flow rate of material through the flow controller is maintained, and where the electronics are configured to determine a leakby value by determining a zero drift (Qdrift) value of the flow controller, determining a flow rate (Qflow) through the flow controller when the flow controller is in the fully closed position and determining the leakby through the flow controller where the leakby is equal to Qflow-Qdrift. 
         [0030]    Preferably, at least one shutoff valve configured to completely stop the flow of material through the flow controller. 
         [0031]    Preferably, at least one shutoff valve is electrically controlled. 
         [0032]    Preferably, the flow sensor is selected from the group: a Coriolis mass flow sensor, a single wire design thermal mass flow sensor, a two wire design thermal mass flow sensor, a positive displacement flow meter. 
         [0033]    Another aspect of the invention comprises a test system, comprising: 
         [0034]    a flow controller having an input/output port; 
         [0035]    at least one shutoff valve fluidly coupled to the flow controller and configured to stop the flow of material through the flow controller; 
         [0036]    a device coupled to the input/output port of the flow controller and configured to determine a leakby value by determining a zero drift (Qdrift) value of the flow controller, determining a flow rate (Qflow) through the flow controller when the flow controller is in the fully closed position and determining the leakby through the flow controller where the leakby is equal to Qflow-Qdrift. 
         [0037]    Preferably, at least one shutoff valve is electrically controlled. 
         [0038]    Preferably, the device is selected from the following group: a portable computer, a test device, a remote processor, a networked computer. 
         [0039]    Preferably, the flow controller includes a flow sensor which is selected from the group: a Coriolis mass flow sensor, a single wire design thermal mass flow sensor, a two wire design thermal mass flow sensor, a positive displacement flow meter. 
         [0040]    Another aspect of the invention comprises a test device, comprising: 
         [0041]    electronics configured to be coupled to the input/output port of a flow controller and configured to determine a leakby value by determining a zero drift (Qdrift) value of the flow controller, determining a flow rate (Qflow) through the flow controller when the flow controller is in the fully closed position and determining the leakby through the flow controller where the leakby is equal to Qflow-Qdrift. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]      FIG. 1  is a block diagram of a flow controller  100  in an example embodiment of the invention. 
           [0043]      FIG. 2   a  is a drawing of flow controller  100  installed into process equipment using external valves in an example embodiment of the invention. 
           [0044]      FIG. 2   b  is a drawing of flow controller  100  installed into process equipment with valves attached or integrated with flow controller  100  in an example embodiment of the invention. 
           [0045]      FIG. 3  is a flow chart for determining the leakby through flow controller  100  in an example embodiment of the invention. 
           [0046]      FIG. 4  is a flow chart showing the steps used to determine Qdrift in step  302  in an example embodiment of the invention. 
           [0047]      FIG. 5  is a flow chart showing the steps used to determine the flow rate (Qflow) through the flow controller in step  304  in one example embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]      FIGS. 1-5  and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
         [0049]      FIG. 1  is a block diagram of a flow controller  100  in an example embodiment of the invention. Flow controller  100  comprises flow sensor  102 , electronics  104 , input/output port  108  and flow control valve  106 . Flow sensor  102  and flow control valve  106  are coupled to electronics  104 . Electronics  104  may be connected to an external device  110  using input/output port  108 . External device  110  may be used to setup flow controller  100  or run diagnostics on flow controller  100 . External device  110  may be a portable computer, a test device, a remote processor, a networked computer or the like. In operation, flow sensor  102  generates a signal indicating the flow rate of material passing through flow controller  100 . Electronics  104  detect the flow signal generated by flow sensor  102 . Electronics  104  adjust flow control valve  106  in response to the signal from flow sensor  102  to maintain the flow rate of material through flow controller  100 . In one example embodiment of the invention, the flow controller may have a plurality of optional input devices  114 , for example an analog voltage input that allows a user to set the flow control valve, a keyboard, or another analog voltage input that allows the user to set the flow controller setpoint command, and a display to allow the user to read flow through the flow controller without attaching an external device to input/output port  108 . 
         [0050]    Flow sensor  102  may be a one wire design thermal mass flow meter, a two wire design thermal mass flow meter, a Coriolis flow meter, a positive displacement flow meter, or any other type of flow meter. Flow control valve may be a needle valve, a butterfly valve, a solenoid valve, or any other type of valve that can be adjusted to a number of different positions between the closed position and the opened position. 
         [0051]      FIG. 2   a  is a drawing of flow controller  100  installed into process equipment using external valves in an example embodiment of the invention. Pipe  206  couples valve  202  to process equipment (not shown). Pipe  208  couples valve  202  to the input side of flow controller  100 . Pipe  210  couples the output side of flow controller  100  to valve  204 . Pipe  212  couples valve  204  to more process equipment (not shown). In one example embodiment of the invention, valves  202  and  204  are external shutoff or blocking valves that can be used to isolate flow controller  100  from process equipment by completely blocking the flow of material through flow controller  100 . In other example embodiment of the invention only one external shutoff valve may be used and placed at either the location of valve  202  or at the location of valve  204 . During normal operation, valve  202  and valve  204  are in the open position allowing flow controller  100  to control the flow rate of material from pipe  206  to pipe  212 . In one example embodiment of the invention, external valves  202  and  204  are manual valves and are manually operated by a user during the process used to determine the leakby value. In another example embodiment of the invention, external valves  202  and  204  are electronically controlled and are operated by flow controller  100 , or by external device  110  during the process used to determine the leakby. In another example embodiment of the invention valves  202  and  204  may be attached directly to, or integrated into, flow controller  100  as shown in  FIG. 2   b.    
         [0052]      FIG. 3  is a flow chart for determining the leakby through flow controller  100  in an example embodiment of the invention. At step  302  the zero drift (Qdrift) of the flow controller is determined. At step  304  the flow rate (Qflow) through the flow controller is determined. At step  306  the leakby through the flow controller is calculated as Qflow-Qdrift. At optional step  308  the leakby is compared against a threshold value. If leakby is greater than the threshold value an error condition is established at step  310 . In one example embodiment of the invention, the leakby may be displayed or reported without being compared to a threshold value. 
         [0053]      FIG. 4  is a flow chart showing the steps used to determine Qdrift in step  302  in an example embodiment of the invention. At step  402 , flow through the flow controller  100  is stopped. The flow may be stopped in a number of different ways. One way is to close a single external shutoff valve to prevent flow into or out-of the flow controller  100 . In another example embodiment of the invention, two external or integrated valves ( 202  and  204 ), one on either side of the flow controller  100 , may be used to stop the flow of material through flow controller  100 . In other example embodiments of the invention, the process pump that drives the flow of fluid through flow controller  100  may be turned off. The external valves, integrated valves, pumps, pressure releases or other devices used to completely stop the flow of material through flow controller  100  are considered to be fluid devices. After turning off the pump or shutting a valve, it may take some time before the flow through flow controller  100  has completely stopped. Even when using a valve on either side of flow controller  100 , it may take some time after closing both valves before the flow through flow controller  100  has stopped. In one example embodiment of the invention, a preset time period is allowed to elapse to ensure the flow through flow controller  100  has stopped. 
         [0054]    Once the flow of material through flow controller  100  has stopped, the zero drift (Qdrift) of the flow sensor  102  is determined in step  404 . Zero drift (Qdrift) is the magnitude of fluid flow as measured by the flow sensor  102  during a no-flow condition with respect to the last zero-point. During a known no-flow condition through the flow sensor  102 , a zero-point is established that equates the indicated flow signal from the flow sensor  102  with zero flow. Zero drift (Qdrift) is the amount the mass flow sensor  102  has drifted at a no-flow condition compared to the zero-point. The zero drift measurement is dependent on environmental conditions, for example temperature. A large change in temperature in the flow controller  100  compared to the temperature of the device when the last zero flow zero-point was established may cause a large zero drift value. Zero drift may be determined from a single data point or may represent a number of different samples. Once the current zero drift (Qdrift) has been determined a new set-point for zero flow may be established by re-equating the current flow signal to zero flow. In one example embodiment of the invention, if the value of zero drift is larger than a threshold value, an error flag or error condition may be established. 
         [0055]      FIG. 5  is a flow chart showing the steps used to determine the flow rate (Qflow) through flow controller  100  in step  304  in one example embodiment of the invention. At step  502  the flow controller  100  is re-integrated into the process system by opening any valves that were shut in step  302  or by turning on any pumps shut off in step  302 . The flow controller  100  is set to “off” or the fully closed position in step  504 . By setting flow controller  100  to the “off” position, any flow through flow controller  100  is due to leakage through flow control valve  106 . In step  506  the flow (Qflow) through the flow sensor  102  is measured. Qflow may be determined from a single data point or may represent a number of different samples. Once Qflow is determined, the leakby through flow controller  100  is calculated as leakby=Qflow-Qdrift. Most flow controllers have a leakby specification. In some example embodiments of the invention if the calculated leakby is greater than the allowed leakby, an error condition may be established. In other example embodiments of the invention the calculated leakby is reported to the user. 
         [0056]    In one example embodiment of the invention, the software or firmware used to determine the leakby value may be run by the internal electronics  104  inside flow controller  100 . In another example embodiment of the invention, an external device  110 , for example a computer, may be connected to input/output port  108  and used to determine the leakby value by running software or firmware that communicates with the flow controller  100 . When using an external device to determine the leakby amount, the external device  110 , the flow controller  100  and at least one valve used to stop the flow of material through the flow controller may be considered as a test system. The external device  110  may be considered as a test device.