Abstract:
Provided is a system and method for concurrently adjusting parameters of a system incorporating separate devices. In a preferred embodiment, a series of amplifiers used in an instrumentation system are able to be adjusted and calibrated concurrently via a simple operation of an unskilled operator. One option provides for this adjustment to occur remotely from the devices.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to control systems and more particularly to concurrent adjustment of multiple devices in a system.  
         BACKGROUND  
         [0002]    For various uses it is necessary to provide a means of converting low level voltage signals from transducers to voltage level signals by amplification of the transducer output. In such systems, a way to efficiently adjust the amplifiers is desirable.  
           [0003]    U.S. Pat. No. 4,510,454 to Sherman, for example, discloses digitally controlled calibration of amplifiers in which the device refers to a memory for the calibration specification.  
           [0004]    U.S. Pat. No. 5,561,395 to Melton et al., discloses an amplifier calibration system that is controlled automatically by a controller that has the specification stored in memory.  
           [0005]    U.S. Pat. No. 5,867,060 to Burkett. Jr. et al., discloses a power delivery system for amplifiers that refers to a memory. The memory is addressed from a system controller.  
         SUMMARY  
         [0006]    A preferred embodiment of the present invention provides an apparatus and method for adjusting electrical devices concurrently. Components include: a controller; a bias circuit in operable communication with the controller and an electrical device(s) to be adjusted: a calibration circuit in operable communication with the controller and the electrical device(s); a digital-to-analog converter (DAC) in operable communication with the controller and the electrical device(s), an input device, an optional display, and an optional transmitter for operation of the apparatus remotely from the electrical device(s). The bias circuit and calibration circuit each may be DACs. The input device may be a keyboard; the optional display may be a liquid crystal display (LCD); and the optional transmitter may be a modem operating at 900 MHz.  
           [0007]    In a preferred embodiment of the present invention, multiple amplifiers of a system, each mounted on its individual card, are adjusted via central circuits performing bias, calibration, and final gain control as centrally directed from a controller. Previously, each of these amplifiers was adjusted individually via the use of three potentiometers (pots) mounted directly on its card. One pot adjusted bias, the second pot calibrated the amplifier, and the third pot set the gain of the final stage. In a preferred embodiment of the present invention a DAC bias circuit and a DAC calibration circuit provide, respectively, the bias and calibration for all amplifier cards while a separate DAC gain control card controls the output from all of the amplifier cards. The microcontroller acts as a central processing unit (CPU), incorporating sufficient memory for providing control of multiple amplifiers, via a suitable interface that permits interchange of electromagnetic energy with the amplifiers in the system.  
           [0008]    In a preferred embodiment of the present invention, a user, through a keypad, loads pre-specified calibration values (scaling relations) that are stored in flash memory. The calibration values are used to translate incoming signals into appropriate engineering units. A technician presses one button and each of the amplifiers in the system are set to zero, calibration is initiated and output gain automatically set to pre-specified levels within seconds. This significantly reduces setup time previously experienced in having to individually set each amplifier card, in the case of a 21 amplifier card system, for example, from an hour to a few seconds. In a preferred embodiment of the present invention, a 900 MHz modem enables a user to do the setup and calibration remotely. Previously recorded levels can be read back from memory, allowing the user to judge whether a transducer is behaving correctly. Optionally, a simple data collection routine is built into the microcontroller run time software for backing up data sent in real time to the user. Also, data may be digitized, stored in memory, and downloaded all at once via modem, for example.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a block diagram of a preferred embodiment of the present invention as used for adjusting a number of amplifiers.  
         [0010]    [0010]FIG. 2 is a schematic of a circuit that may be used with the preferred embodiment of the present invention shown in FIG. 1.  
         [0011]    [0011]FIG. 3 is a logic diagram for a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIG. 1 is a block diagram depicting the main functions performed by a preferred embodiment. The amplifiers  16 ,  18 ,  20  to be controlled and calibrated are connected via a suitable connector  38  to the three main functions that bias  24 , calibrate  26 , and provide gain control  40  for them. The three main functions are controlled by a suitable microcontroller  22  that may be accessed via a keypad  52  and a modem  44 , and may have a display for real time review of activities related to the control and calibration of the amplifiers  16 ,  18 ,  20 . Further, a computer  56  may be provided for access to stored specifications and additional computational resources.  
         [0013]    Referring to FIG. 1, a preferred embodiment of the present invention supports multiple amplifiers e.g., signal amplifier  10  (Amp  1 ), signal amplifier  12  (Amp  2 ) and signal amplifier  14  (Amp n). Shown is a signal input  16 , e.g., an output of a transducer, to signal amplifier  10 , a signal input  18  to signal amplifier  12 , and a signal input  20  to signal amplifier  14 . At the heart of a preferred embodiment of the present invention is a microcontroller  22  that may be embodied in a microcomputer. A preferred embodiment of the present invention also includes a bias circuit  24  and a calibration circuit  26 , a DAC gain control circuit  40 , an optional modem  44 , an optional LCD display  48 , an optional keypad  52 , and a optional laptop computer  56 . Further, paths  28 ,  30 ,  42 ,  46 ,  50 ,  54 , and  58  provide operable communication from the microcontroller  22  to the bias circuit  24 , the calibration circuit  26 , the DAC gain control circuit  40 , the optional modem  44 , the optional LCD display  48 , the keypad  52 , and the optional laptop computer  56 , respectively. The DAC gain control circuit  40  communicates with amplifiers  10 ,  12  and  14  via a path  36 . Paths  32  and  34  provide communication between the individual amplifiers  10 ,  12  and  14 , via a bus  38  and paths  39 , for example, and the bias circuit  24  and calibration circuit  26 , respectively.  
       EXAMPLE  
       [0014]    Refer to FIG. 2. A preferred embodiment of the present invention includes a circuit that may have both a positive input signal  60  and a negative input signal  62 , both of which are represented by the paths  16 ,  18 , and  20  in FIG. 1, to a differential operational amplifier  64 . The differential operational amplifier  64  is in communication with a summing junction  66  that in turn is in communication with an inverting operational amplifier  68 . The inverting operational amplifier  68  communicates via paths  70  and  72  with a sample and hold circuit  74 , in turn in communication with a digital control switch  78  via a path  76 . The digital control switch is in communication with the summing junction  66  through two paths  80  and  82 . A calibration circuit  26  is in communication with a microcontroller  22  via a path  30  and also communicates with the digital control switch  78  through a path  88 . A shift register  24  for balancing the amplifiers communicates with the digital control switch  78  via a path  92  and with the microcontroller  22  via a path  28 . A DAC  40 , used for gain control of the final stage, is fed via a path  70  and communicates with the microcontroller  22  via a path  36  and with an inverting operational amplifier  104  via a path  102 .  
         [0015]    Again refer to FIG. 2, an overview schematic of the three main stages involved in providing calibration and control of multiple amplifiers  16 ,  18 ,  20 . In stage  1 , an input signal is provided on paths  60 ,  62  to a differential amplifier  64  from a bridge sensor (not separately shown) having a low signal level. Should the input be a single-ended input, the positive path  60  is grounded and only the inverter (negative) path  62  is used. The microcontroller  22  provides a serial bit stream on path  28  to a shift register  24  that converts the serial bit stream to a parallel one on path  92  used to control a digital switch  78 .  
         [0016]    The signal from the differential amplifier  64  of Stage  1  is summed at the summing junction  66  and inverted in the inverting amplifier  68 , so that the signal on path  70  is opposite in polarity to that amplified by the differential amplifier  64 . The signal on path  70  is provided to a sample and hold circuit  74  on path  36  that latches this signal when commanded and produces a constant level output signal on path  76  equal to the level of the signal originally provided on path  72  at the initiation of the command.  
         [0017]    When commanded via the microcontroller  22  using the parallel bit stream on path  88  resulting from the calibrate circuit  26 , the digital switch  78  switches the latched and inverted signal on path  76  through to path  82 . This signal is the exact inverse of the signal provided by the differential amplifier  66  so that when the two signals are summed in the sunning junction  66 , the result is the “null signal” that biases to a null voltage level.  
         [0018]    Upon occurrence of the null biasing, the digital switch  78  accepts the calibration signal on path  88  from the “Calibrate” circuit  26  as representative of a user-specified level initiated by the microcontroller  22 . This sets up the remaining two stages. Since the other two signals have nulled each other, this calibration signal on path  80  is the only signal of consequence passed to the remaining stages over the summing junction  66 . It is passed through the inverting amplifier  68  over path  70  to the DAC  40  that serves to control the gain of the amplifiers  16 ,  18 ,  20 .  
         [0019]    The DAC  40  varies an output voltage on path  102  that tracks the input voltage on path  60 ,  62  in a linear relationship. That is, the output voltage is equal to the input voltage multiplied by a constant, the value of the constant can be greater than 1 or a fraction, being provided over path  36  from a user-specified value in the microcontroller  22  to the DAC  40 . Thus, the DAC, not normally used for gain control, provides gain control in Stage  2 .  
         [0020]    Upon setting the gain in Stage  2 , the calibration signal from the DAC  40  is passed over path  102  to a second inverter amplifier  104  to reverse the polarity of the signal to that of the initial input signal on path  60 ,  62 . The output of the second inverter amplifier  104  is provided on path  108  to calibrate, bias, and provided gain control to amplifiers  16 ,  18 ,  20 .  
         [0021]    When measurements are being recording using the amplifiers  16 ,  18 ,  20 , the calibration signal from path  108  is removed via a command provided via the digital switch  78 , since the calibration is used only at times of initial setup and periodic calibration. Being able to readily calibrate multiple devices, such as amplifiers  16 ,  18 ,  20 , enables each device to convert signals from sensors, such as transducers, to signal levels that are all in an appropriate range for easy digitizing.  
         [0022]    Refer to FIG. 3 for the logic chart of a preferred embodiment of the present invention. A preferred embodiment of the present invention is powered on  110  and a welcome message is printed  112 . If a setup switch  114  is set to on, a setup routine for calibration and gain setup  116  is initiated. If the setup switch  114  is not set to on the next operation determines if the zero switch  118  has been set to on. If the setup switch  114  was set on, the setup routine  116  was initiated, and the zero switch  118  was set to on, the calibration outputs are disabled and all amplifier channels are set to zero  120 . If neither the setup switch  114  nor the zero switch  118  are set to on, the next operation is at the calibration switch  124 . After disabling calibration and zeroing all channels, the calibration switch  124  may be set to on or left off. If it is set to on, calibration is enabled on each channel associated with an amplifier card. If not set to on, the next step is keyboard input  128 . If neither the setup  114 , zero  118 , nor calibration  124  switches are set to on, the next step is keyboard input  128 . If calibration has been enabled  126  and there is a keyboard input  128 , the keyboard input  128  is captured or “trapped”  130  for further use. If neither the setups  114 , zero  118 , nor the calibration  124  switches are set to on and no keyboard input  128  is made, the next step is data collection  132 . If the keyboard input  128  has been trapped  130 , then a collect data flag  132  is set and a data collection setup routine  134  is initiated. If none of switches  114 ,  118 ,  124  are set to on and there is no keyboard input  128 , the collect data flag is set  132  and the operation may be reiterated at the input to the setup switch  114 . If the data collection setup routine  134  has been initiated for a particular data set, the system is now available for re-set and reiteration at the setup switch  114 .  
         [0023]    It will be appreciated that the above-described apparatus discloses means for quickly and efficiently calibrating multiple amplifiers arranged in a system such as may be used in an instrumentation setup for taking test data.  
         [0024]    While the present invention has been described in connection with the preferred embodiments of the various elements, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the present described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.