Abstract:
Embodiments of the invention relate generally to a configurable analog input channel with galvanic isolation. In one embodiment, the invention provides a configurable input channel for selectively receiving one of a plurality of different analog sensor inputs. The input channel includes an interface for implementing switch settings for a selected type of input signal; a set of input terminals, wherein at least two of the set of input terminals are selectively utilized to correspond with the selected type of input signal; an analog-to-digital converter for converting the input signal into a digital output, wherein an operation of the analog-to-digital converter is determined based on the switch settings; and an isolation barrier for isolating the configurable input channel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Embodiments of the invention relate generally to systems for sensing analog control data, and more particularly to a system having a universal input channel that is configurable to allow one of several different analog input types to be received via a single set of terminals. 
         [0002]    In complex control systems, such as those that monitor turbines and the like, it is typically necessary to monitor or sense different types of input signals, e.g., thermocouple inputs, RTDs (resistance temperature detectors), currents, voltages, and resistance. In order to accomplish this, different types of sensing modules are employed to sense different types of input. A common approach is to utilize sensing modules that have a fixed number of input channels (e.g., 24) for receiving a particular type of input. For instance, a first set of sensing modules may be utilized for sensing N thermocouple inputs, a second set of sensing modules may be utilized for sensing M RTD inputs, etc. 
         [0003]    However, because each sensing module is manufactured with a standard number of input channels, each sensing module will likely be deployed with unused input channels. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    A configurable input channel is provided capable of receiving one of several different input types in which the channel adjusts its span and input characteristics to match the input type. 
         [0005]    In one embodiment, the invention provides a configurable input, comprising: an interface for implementing switch settings for a selected type of input signal; a set of input terminals, wherein at least two of the set of input terminals are selectively utilized to correspond with the selected type of input signal; an analog-to-digital converter for converting the selected type of input signal into a digital output, wherein an operation of the analog-to-digital converter is determined based on the switch settings; and an isolation barrier for isolating the configurable input channel. 
         [0006]    In another embodiment, the invention provides a control system comprising: a plurality of configurable input channels for selectively receiving different analog sensor inputs, each configurable input channel comprising: an interface for implementing switch settings for a selected type of input signal; a set of input terminals, wherein at least two of the set of input terminals are selectively utilized to correspond with the selected type of input signal; an analog-to-digital converter for converting the selected type of input signal into a digital output, wherein an operation of the analog-to-digital converter is determined based on the switch settings; and an isolation barrier for isolating the configurable input channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
           [0008]      FIG. 1  shows a block diagram of a generalized architect of a configurable input channel according to an embodiment of the invention; 
           [0009]      FIG. 2  shows a table of input types and internal flows of the configurable input channel according to an embodiment of the invention; and 
           [0010]      FIG. 3  shows an illustrative circuit for implementing a configurable input channel according to an embodiment of the invention. 
       
    
    
       [0011]    It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring now to the drawings,  FIG. 1  depicts a generalized architecture of a configurable input channel  10  that can universally receive one of several different types of analog sensor inputs  34 . Analog sensor inputs  34  are provided, e.g., via a twisted wire pair from a sensor located on a turbine  35 . In this illustrative embodiment, configurable input channel  10  can be configured to receive one of a thermocouple input, an RTD input, a current loop input, or a voltage input. Configurable input channel  10  is configured for a particular type of analog sensor input  34  by: (1) inputting appropriate configuration settings  14  for a desired input type; and (2) connecting the analog sensor inputs to the appropriate terminals T 1 , T 2  and/or T 3 . 
         [0013]    Based on the configuration settings  14  and connections, analog sensor input  34  is processed in a particular manner and converted to a digital output  28 , which is fed to a controller  32  via a digital isolation barrier and isolated power source  30 . Controller  32  likewise receives digital data from a plurality of other configurable input channels  10 ′ (each having its own digital isolation barrier and isolated power source  30 ′). Digital isolation barrier and isolated power source  30  provides galvanic or electrical isolation from other electrical components within a complete control system, thus satisfying the commercial requirement for point-isolated channels. Galvanic isolation is the principle of isolating functional sections of electric systems so that charge-carrying particles cannot move from one section to another, i.e., there is no electric current flowing directly from one channel  10  to the next  10 ′. Energy and/or information can still be exchanged between the channels by other means, such as by capacitance, induction, electromagnetic waves, optical, acoustic, or mechanical means. 
         [0014]    Configurable input channel  10  includes a programmable interface  12  that implements switch settings  16  based on the inputted configuration settings  14 , using, e.g., a switch control register. The switch settings  16  will internally configure the circuitry for processing a particular type of input. Note that rather than a programmable interface  12 , manual jumpers could be utilized to implement switch settings  16 . 
         [0015]    Configurable input channel  10  includes three input terminals (T 1 , T 2 , T 3 ), of which a predetermined two or three will be utilized for receiving an analog sensor input  34 .  FIG. 2  provides an illustrative table that shows which terminals are to be used for a given input. For instance, for a thermocouple or voltage input configuration, terminals T 1  and T 2  are utilized for V 1  and V 2  voltage inputs, and T 3  is not utilized; for a current loop input configuration, T 1  and T 2  are utilized for a current input and a current output, respectively; and for an RTD input configuration, T 1  is utilized for a first current (Current  1 ) output and a first voltage V 1  input, T 2  is utilized for a second current (Current  2 ) output and a second voltage V 2  input, and T 3  is utilized for a Current  1 +Current  2  input and a third voltage V 3  input. 
         [0016]    Thus, depending on the input type, terminals T 1 , T 2 , T 3  may be configured as simple input terminals (e.g., thermocouple, voltage), or be configured for both input and output (e.g., current loop, RTD). The table of  FIG. 2  also provides channel switching and measurement calculations for the four different input types. It is understood that additional or a different combination of input types could likewise be implemented and fall within the scope of the invention. 
         [0017]    As shown in the generalized example of  FIG. 1 , conversion of the analog sensor input  34  to a digital output  28  is obtained using circuitry including a serial A/D (analog-to-digital) converter  26 . Use of serial A/D converter  26  provides for a channel that can be separately powered and isolated. Control within the channel is based on switch settings  16  for the A/D reference and input selections as well as programmable current sources. Switch settings  16  generally control: a T 1 /T 2  Rc selection  18  for configuring a current sensing resistor  24  for T 1  and T 2 ; a current source selection  20 ; and an A/D voltage setting  22 . Terminals T 1 , T 2 , T 3  are separated from the configurable input channel  10  with a protection circuit  36 . 
         [0018]      FIG. 3  depicts a more detailed example of a circuit  40  for implementing a configurable input channel. Note there are five switch controls S 1 -S 5   42  in circuit  40 , and switches S 1 -S 5  are provided both internally to the serial A/D  44  and externally. 
         [0019]    S 1  selects the A/D reference either from a volt source  46  or from the voltage across a sensing resistor Rd. The sensing resistor connection is for RTD sensing, and provides a ratiometric reading. Resistor Rd is for example on the order of a hundred ohms. 
         [0020]    S 2  and S 3  provide for the selection of a current sensing resistor Rc across terminals T 1  and T 2 . Use of these two switches allows for the switch resistance to be compensated for within the circuit, whereas a single switch would add the unknown switch resistance to that of resistor Rc. The second switch allows the voltage sensing to be across the terminals or across resistor Rc. Resistor Rc is for example on the order of a hundred ohms. 
         [0021]    S 4  and S 5  provide for current paths from a dual matched current source (within the A/D as shown, but may be a separate matched source). The two resistors Ra are used for the burnout pullup/pulldown voltages, where the current sources are selected to be active only on a single source (forcing a voltage on one of the resistors Rb for the pullup and a much lower voltage on the second resistor Rb due only to leakage currents giving a pulldown voltage). Resistors Ra are for example on the order of tens of megaohms, while resistors Rb are for example on the order of a thousand ohms. 
         [0022]    Internal switches within the serial A/D  44  allow for: matched current source magnitudes and routing; input selection from four input pins; and voltage reference level and source. 
         [0023]    Control of the switches and serial A/D  44  is via registers accessed by serial ports. Each channel has two ports—the A/D  44  with its internal registers both to write control settings and to read back data, and the switch control register. Each isolated channel is totally separate from the other channels—where the controlling device (e.g. microcontroller as in  FIG. 1 ) has a quantity of serial channels to control. In an implementation, the SPI (serial peripheral interface) protocol with a clock, select, master to slave data, and slave to master data could be used. The multiple ports could share a common clock and master to slave data pair of signals, with the selects specifying which channel is being controlled as well as multiplexing the multiple slave to master data responses. 
         [0024]    Additional circuitry not shown in  FIG. 3  includes protection circuits on the terminals (e.g., low ohm resistors in series to limit currents through clamping diodes to the local isolated common) and a cold point measurement circuit (e.g., a digital sensor located adjacent to the terminals). 
         [0025]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0026]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any related or incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.