Abstract:
The present circuitry provides for an expansion of loop powered technology preferably employed on 4-20 mA. The invention provides for extracting energy from current loops for use in displays, alarms, controls and communication. Further, the circuit allows for a reporting of instrument status and loss of signal to eliminate operator error in assuming the meter is faulty when in actuality a loss of signal has occurred.

Description:
CROSS REFERENCE 
     This application claims the benefit of provisional patent application Ser. No. 61/855,422, filed May 15, 2013, the disclosure of which is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Loop powered technologies are well known in the art and include: U.S. Pat. No. 6,285,094, entitled “Loop-Powered Current-Loop Controller”, issued to Fest on Sep. 4, 2001; U.S. Pat. No. 7,477,080 entitled “Current Loop Powered Isolator”, issued to Feast on Jan. 13, 2009; and, U.S. Pat. No. 7,684,768 entitled “Loop Powered Current-Loop Transmitter”, issued to Fest on Mar. 23, 2010; all of which are incorporated hereinto by reference. 
     SUMMARY OF THE INVENTION 
     The present circuitry provides for an expansion of loop powered technology preferably employed on 4-20 mA. The invention provides for extracting energy from current loops for use in displays, alarms, controls and communication. Further, the circuit allows for a reporting of instrument status and loss of signal to eliminate operator error in assuming the meter is faulty when in actuality a loss of signal has occurred. 
     Further, the circuit provides for exceptional reporting for machinery and computerized supervisory control systems without requiring external power other than the one already in existence in a 2-wire current loop application. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts the schematic diagram of the preferred embodiment of the Loop Powered Meter/Controller according to the present invention. 
         FIG. 2  depicts the schematic diagram of the preferred embodiment of the retransmission section to the present invention. 
         FIG. 3  depicts the schematic diagram for the preferred embodiment of the signal inversion, gain and offset circuit of the present invention. 
         FIG. 4  depicts a system schematic for the present invention 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A primary embodiment of the present invention consists of a signal or loop powered controller, which is electrically isolated between the input and output portions of the circuit. The controller measures an input signal from an input current loop and transmits an output signal over an optical isolator, to a desired output current loop. This allows for speedy automatic control of electrical systems. The invention additionally has a bargraph display which allows easy observation of the signal level and a failure alarm which will alert the user to when the input signal power is failed. 
     As shown in  FIG. 4 , the invention uses a microcontroller ( 200 ) to generate a pulse-width modulated output that is sent to an optical isolator ( 250 ) that separates input and output halves of the controller. The input half has a loop powered signal input circuit ( 210 ), which generates a power supply for a microcontroller and converts the input signal into a positive signal for input to the A/D converter. The power supply also charges an energy storage device ( 220 ), which supplies power to the microcontroller when no loop or signal is present. The microcontroller receives the converted input signal and generates at least two outputs: a constant pulse output which is connected to a watch dog timer alarm that is triggered if and when the pulse ceases, and a pulse width modulated control signal output, which is determined based on the input signal and is sent to the optical isolator. The microcontroller also controls a digital display, which may be a bargraph display. The optical isolator is connected to the signal transmitter circuit ( 260 ), which is powered from a current loop of the device being controlled. 
     In the present embodiment, an input signal ( 211 ,  212 ) Is supplied to the controller, the signal input circuit uses the current provided by the input signal to generate a voltage ( 213 ) as well as a ground ( 214 ) that powers the microcontroller and the input circuit. This same voltage charges the energy storage device, which delivers power to the microcontroller ( 200 ) when an input signal is not present. The input signal ( 211 ,  212 ) Is linearly transformed by the input signal circuitry into an intermediate signal ( 215 ,  216 ) which is always positive relative to the A/D ground, and input to the A/D converter of the microcontroller. The microcontrollers controls the display bus ( 231 ) to generate a representation of the signal measurement on the digital display ( 230 ), as well as a constant pulse ( 241 ) that is output to the watch dog timer ( 240 ) on a pulse-width modulated output. When the microcontroller detects a failure of the input signal, or when the microcontroller is no longer powered, it stops sending the constant pulse output, whereupon the watch dog timer alarm is triggered. The microcontroller also outputs a pulse-width modulated signal ( 251 ) representing the signal measurement to the optical isolator ( 250 ), which acts as an isolation barrier that electrically separates the input signal circuit ( 210 ) from the transmitter circuit ( 260 ). The optical isolator acts as a switch in the transmitter circuit, which opens and closes as the pulse width modulated signal is sent to the optical isolator, whereupon the signal is averaged by the output signal and returned to the output current loop ( 261 ,  262 ) as a current proportional to the signal level. 
     Referring to  FIG. 1 , it is important to note that, similar to an analog meter, the subject invention is powered by the signal it measures whether it is Voltage or current (DC or AC) or current loop in nature as long as the signal can supply enough energy (&gt;5 mW at present) to power the invention. 
     Input Voltage Signal Measurement Description: 
     The most positive voltage is applied at terminal  10 . The most negative voltage is applied at terminal  12 ; terminal  14  is connected to terminal  10 . Resistor  16  protects LED  22  from over-voltages and allows it to clamp the input voltage to a level acceptable (VCC) by the componentry. Resistors  20  and  18  form a voltage divider for the internal analog to digital converter (A/D) of microcontroller  60  to measure and convert to digital format. 
     Resistor  16  also serves as a current limiter when measuring voltage. When measuring currents, its value is zero (0) Ohms. Rectifier  24  serves two purposes, it prevents reverse polarity being applied to the circuitry only allowing positive (+) polarity in direct current measurements and #2, it rectifies the A.C. input signal to power the electronics in conjunction with LED  22  that regulates it. Because the total power of the subject invention is a few milli Watts, a half wave rectified power supply filtered by ESD  32  is sufficient for reliable operation. 
     Input Current Signal Measurement Description: 
     The positive (+) loop is applied to terminal  10  and the negative (−) loop to terminal  12 . The voltage drop across LED  22  sets the VCC magnitude for the circuitry and also indicates that the loop is “On,” resistor R 18  shunts the loop current to convert it to voltage for A/D conversion by microcontroller  60 . The invention has provisions for external power for measurements of signals too small to power the electronics. In this case, V+ is applied at terminal  10 , V− at terminal  12  and + signal at terminal  14  with − signal common to V-terminal  12 . Resistors R 20  and R 18  attenuate the signal for A/D conversion. 
     The above explanations are the only difference between voltage signal power and current signal power. All else is common for both operations. Resistor  34  limits the current into ESD (Energy Storage Device)  32  while the system is operating under normal conditions. ESD  32  serves two purposes, first it filters and averages A.C. when measuring A.C. signals, and second, should the signal input fail, the charge on ESD  32  will power the electronics via diode  36 . Diode  24  will prevent the ESD  32  from discharging into the source should a short circuit occur at its input terminals  10  and  12 . The charge in ESD  32  is of sufficient magnitude to allow uC  60  upon detection of a lack of signal at the junction of items  18  and  20  to arm its failure detect LED  30  to flash a warning on its display and transmit a distress message via its serial port isolators  50  to supervisory equipment and local alarms via isolators  40 ,  42 ,  44  and  46 , which can be any opto-isolated (or not) electronic switch such as transistors, SCR, triacs or solid state relays, as well as lamps, etc. Resistors  41 ,  43 ,  45 ,  47  &amp;  49  limit the current into the LED of isolators  40 - 48  respectively. 
     Signal inversion and correction circuitry  26  also contains manual zero and span adjustments for ease of calibration in place or in addition to the serial input algorithm for calibration. The inversion scheme is necessary to allow the A/D of uC  60  to operate above (+) and below (−) its ground (Vss) level without the use of DC-DC converters. 
     The several algorithms written into uC  60  allows the uC to drive the displays (digits and bargraph) item  28  in a multitude of fashions including, multicolor using RGB (red, green and blue) LEDs. The firmware also allows for driving dot matrix graphic displays only limited by uC  60  output ports available and its firmware. 
     The present invention includes isolated multichannel scanning via isolators  54  and  56 , such as used in triple redundant controllers as well as current loop retransmission item  48 . The above is representative of the flexibility of the invention and it is not intended to show or limit the scope of the invention but on the contrary, to demonstrate the unlimited applications of the invention only limited by the knowledge of the designer and the capabilities of the hardware available. 
     In  FIG. 2 , the written algorithm into uC 60  contains a PWM (Pulse Width Modulation) module that drives isolator  48  at its inputs. The output of isolator  48  is excited by a constant current and constant voltage scheme that ensures*an accurate and constant 1:1 transfer ratio to the V-I (Voltage to Current) transmitter  62 . Constant current source  64  supplies a parasitic ˜1 mA of transmitter section current that is clamped to a constant voltage by Zener diode  66 . In a preferred embodiment, the values of the resistor  72  and input voltage is selected so that the voltage at “A” is always higher than the voltage at the resistor  72 , which prevents current from flowing through the Zener diode and maintains a constant voltage drop across it. The constant current of  64  is determined by the ratio of resistors  68  and  70 . 
     It is important to note that any excess currents produced by  64  are summed to the total output current of  62  to avoid non-linearity. This is accomplished by the connection of zener diode  66  to V-I converter  62  at its junction with resistor  72 , which itself is part of the ratio between it and resistor  74  that determines the gain of  62 . When the PWM signal of isolator  48  is converted to variable voltage by the current of  64  at point “A,” transferred to point “B” by isolator  48  and averaged by resistor  76  and capacitor  78  closing the circuit for smooth current transmission output at terminals  90  (+) and  92  (−) allowing the transmitter to drive loads in a “source” or “sink” fashion. Capacitors  80 ,  82  and  84  filter glitches that might be caused by load changes and/or PWM steps. LED  86  serves two purposes, first it prevents reverse voltage from damaging the transmitters  62  and  64 , and secondly, it visually indicates proportionally the current flow at the transmitter&#39;s output. 
       FIG. 3  shows the circuitry for the signal inversion, offset and gain circuit ( 26 ). Analog to digital converters embedded in micro-controllers are known for being limited to unipolar and ground referenced inputs, forcing designers to utilize DC-DC converters and additional hardware to achieve desired high accuracy bipolar or floating signal operation. The embodiment includes a unique scheme to overcome those limitations of low-cost standard micro-controllers with embedded A/D. It&#39;s worthwhile to note that this novel configuration allows the A/D to process unipolar negative or positive signals with reference to micro-controller ground, as well as bipolar differential signals, without DC-DC converters or absolute value amplifier techniques. 
     Power is supplied at VCC by the same voltage drop across LED  22  in  FIG. 1 . Capacitors  102  through  110  are used as by-pass filters on power and signal lines. Voltage reference  120  provides the 1.25V references for the amplifiers  100 : 1  &amp;  100 : 2  inputs through resistors and potentiometers  122  through  132  and  142 . Potentiometers  130  &amp;  132  allow for manual zero and span adjustments of the output signal to the A/D at +Out and −Out. Resistors  146  &amp;  148  balance the impedances into the A/D inputs. 
     Negative inputs with reference to A/D ground are applied to amplifier  100 : 1  at Pin  2  (−) that forms a summing junction with resistors  126 ,  130  &amp;  128 . In this case, resistors  136  &amp;  138  are zero (0) Ohms and resistors  134  &amp;  140  are not used. For positive signals, resistor  126  is grounded and positive (+) input is applied either at +Signal A through resistor  134  whose value is the same as resistor  136 , forming a divider into amplifier  100 : 1  positive (+) Input or at resistor  140  (+Signal B), which determines the gain of amplifier  100 : 2  with resistor  138 . For bipolar and differential signals, inputs are applied at resistor  134  (A) and resistor  140  (B). Amplifier  100 : 1  and associated zero &amp; span circuitry retain the manual adjustments. 
     The inversion gain and offset circuit may be configured differently depending on the user&#39;s needs. The signal that is developed across resistor  18  is the signal input for the circuit, and when current is nominally flowing in the positive direction the signal is typically negative. For unipolar signals, the −S/−V line in  FIG. 1  is connected to the −SIG line in  FIG. 3 , while the +S line is connected to either +SIGA or +SIGB. For bipolar signals the +S line is connected to +SIGA and the −S/−V line is connected to the +SIGB input. 
     The choice of resistor values in the inversion, gain, and offset circuit must be carefully considered to ensure that both signals remain positive relative to the A/D ground. 
     Care must be taken in the layout of the componentry to avoid crosstalk and stray capacitances from disturbing the quality of the signal due to high frequency operation of the micro-controller. 
     Referring to  FIG. 1 , the microcontroller may also be equipped with one or more UART (serial) outputs, which can be used to communicate with a computer or peripheral device, which can be electrically isolated from the circuit using transformer isolators ( 50 ,  52 ,  54 ,  56 ). 
     Referring to  FIG. 1 , the microcontroller may also be equipped with limit outputs, which may be connected to external circuits or devices via additional optical isolators ( 40 ,  42 ,  44 , and  46 ). The optical isolators allow the microcontroller to communicate with other electronic circuits or devices using TTL logic. For each limit output a resistor ( 41 ,  43 ,  45 , and  47 ) limits the current that can flow into the optical isolator input. The optical isolator allows the controller to remain electrically isolated from other circuits. 
     The above described novel circuitry eliminates the need for generating a negative supply and absolute value amplifiers when inputting bipolar/differential signals into generic A/D in micro-controllers. 
     The invention provides for a variety of uses obvious to those of ordinary skill in the art, including, but not limited to: 
     A: A loop powered (powerless) bargraph-digital meter. 
     B: An isolated loop powered input and externally powered bar-digital controllers. 
     C: An isolated A.C. signal powered (powerless) meter in conjunction with the referenced patents. 
     D: An isolated input to output (I/O) loop/signal powered bar-meter with isolated outputs bases with the referenced patents. 
     E: An isolated serial I/O or analog input signal 4-20 mA transmitter/controller (alarms) with bargraph or digital display. 
     F: A second version illuminates multicolor  15  segment (Alphanumeric) display instead of multicolor bargraph, The alphanumeric display is capable of communicating to operators directly (serially or by the signal) avoiding operator errors of interpretations. 
     Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference cited in the present application is incorporated herein by reference in its entirety. 
     Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. Reference numbers recited in the claims are exemplary and for ease of review by the patent office only, and are not limiting in any way. In some embodiments, descriptions of the inventions described herein using the phrase “comprising” Includes embodiments that could be described as consisting of, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase “consisting of” is met. 
     The reference numbers recited in the below claims are solely for ease of examination of this patent application, and are exemplary, and are not intended in any way to limit the scope of the claims to the particular features having the corresponding reference numbers in the drawings.