Abstract:
A measurement method and system in which a plurality of sensors are scattered about the system. One or more universal data concentrators are deployed in the areas where the sensors are concentrated. Each data concentrator is connected to one or more computers. Unique configuration data is provided to each data concentrator for its unique sensor type complement. Each data concentrator configures itself based on its configuration data. This allows the use of a universal data concentrator and, thus, one part number.

Description:
FIELD OF THE INVENTION 
   This invention relates to a measurement system and method. 
   BACKGROUND OF THE INVENTION 
   Modern aircraft systems include a large number of sensors scattered over a variety of localized and remote locations. To reduce aircraft wiring, weight, cost, and complexity, aircraft systems designers are currently moving away from centralized electronics, where all sensors are wired back to one central location, in favor of a Remote Data Concentrator (RDC) concept. This concept minimizes aircraft wiring by remotely locating a number of RDCs near the areas of highest sensor concentration. This allows all nearby sensors to be connected by short cabling to one RDC, which is in turn connected to an aircraft data bus. Because there is a wide variety of sensor types, each with its unique interface requirements, an RDC may contain several unique and dedicated interface circuits, resulting in many different types of unique RDCs throughout an aircraft. Ideally, all RDCs for a specific aircraft application would be common, with a few spare circuits to handle the sensor interface variations from one location to another. This is rarely the case, so a practical compromise must be found between multiple RDC versions (part numbers), and multiple spare channels (several unused) to accommodate dissimilar sensor requirements at various locations. Both solutions add weight and cost that offset some of the advantage of the RDC approach. Thus, a problem that arises is how to reduce the number of different types of RDCs required without adding weight and cost. 
   SUMMARY OF THE INVENTION 
   The system and method of the present invention solves the aforementioned problem by providing a universal RDC with a versatile/configurable measurement circuitry that allows a single RDC part number to be used throughout the measurement system. The universal RDC is programmable according to a configuration file that identifies the sensor type that is connected to each channel of the RDC as well as the parameters of scaling, excitation signals and return signals for each sensor type. This enables the universal RDC to be used with a large number of different sensor types. 
   In one embodiment of the measurement system of the present invention, at least one computer provides configuration data to at least one data concentrator. The data concentrator comprises a processor and a plurality of channels that provide a universal interface for a plurality of sensor types. The configuration data includes an assignment of each of the channels to one of the sensor types. The processor runs a configuration program that configures the processor based on the assignment. 
   In another embodiment of the measurement system of the present invention, the processor, after being configured, runs a measurement procedure that via the channels provides sensor excitation signals and receives sensor return signals that are based on the assigned sensor types. 
   In another embodiment of the measurement system of the present invention, the processor executes discrete Fourier transform procedures to provide precision measurements over a broad range of configurable frequencies and amplitudes. 
   In another embodiment of the measurement system of the present invention, the configuration data further includes a configuration file that designates excitation signal parameters and sensor return signal characteristics for each sensor type. The processor generates the sensor excitation signals and processes the sensor return signals based on the excitation signal parameters and the sensor return signal characteristics. 
   In another embodiment of the measurement system of the present invention, the data concentrator is one of a plurality of substantially identical data concentrators. The configuration data is unique to each of the data concentrators. 
   In a method embodiment of the present invention, configuration data is provided to at least one data concentrator that comprises a processor and a plurality of channels that provide a universal interface to a plurality of sensor types. The configuration data includes an assignment of each of the channels to one of the sensor types. The processor and the channels are configured based on the assignment. 
   In another embodiment of the method of the present invention, a measurement procedure is run that via the channels provides sensor excitation signals and receives sensor return signals that are based on the assigned sensor types. 
   In another embodiment of the method of the present invention, the step of running uses discrete Fourier transform procedures to provide precision measurements over a broad range of configurable frequencies and amplitudes. 
   In another embodiment of the method of the present invention, the configuration data further includes a configuration file that designates excitation signal parameters and sensor return signal characteristics for each sensor type. A measurement procedure provides the sensor excitation signals and processes the sensor return signals based on the excitation signal parameters and the sensor return signal characteristics. 
   In another embodiment of the method of the present invention, the data concentrator is one of a plurality of substantially identical data concentrators. The configuration data is unique to each of the data concentrators. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and: 
       FIG. 1  is a block diagram of a universal sensor system of the present invention; 
       FIG. 2  is a block diagram of a remote data concentrator of the system of  FIG. 1 ; and 
       FIG. 3  is a block diagram of the random access memory of  FIG. 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a measurement system  20  of the present invention is shown in the environment of an aircraft  22 . It will be appreciated by those skilled in the art that measurement system  20  can also be used in other environments that have multiple sensors scattered in a number of locations. For example, measurement system  20  may be used in other vehicular systems, such as ships, trains, space vehicles, tanks, trucks or a complex industrial control system. 
   Measurement system  20  includes a bus  24  that interconnects one or more computers  26  and a plurality of RDCs  30 . Each RDC  30  is placed in a location that is in the vicinity of a plurality of sensors  32 . These locations may be located near a computer  26  or remote from the computers  26 . Computers  26  may be any suitable computers that process data. For example, computer  26  may be a personal computer, a workstation, a large data processor or any system component requiring the sensor data. 
   RDCs  30  are substantially identical (i.e., universal), but are individually configured based on configuration data that may be provided by one or more of computers  26 . That is, the configuration data for each RDC is unique to the set or group of sensors  32  with which the RDC is connected. 
   Referring to  FIG. 2 , RDC  30  includes a processing unit  40  that is connected with bus  24  via a serial data interface  41  and with a sensor excitation unit  50  and a sensor return signal unit  70 . Processing unit  40  includes a digital signal processor  42 , a read only memory (ROM)  44  and a random access memory (RAM)  46 . A crystal oscillator  48  provides a clock signal to digital signal processor  42 . 
   Sensor excitation signal unit  50  includes a digital to analog converter (DAC)  52 , a set of amplifiers  54 , electromagnetic interference (EMI) filters  56  and a set of selector switches  58 . Sensor excitation signal unit  50  is arranged to provide excitation signals on a plurality of connectors  60 ,  61 ,  62 ,  63 ,  64 ,  65  and  66 . To this end, DAC  52  converts a digital excitation signal provided by DSP  42  to an analog signal. Switches  58  respond to a selector signal from DSP  42  via a line  55  to provide excitation signals on one or more desired connectors. 
   Sensor return signal unit  70  includes an analog to digital converter (ADC)  72 , an input amplifier  74 , a multiplexer  78  and EMI filters  76 . Sensor return signal unit  70  is arranged to receive sensor return signals on a plurality of channels or connectors  80 ,  81 ,  82 ,  83 ,  84 ,  85  and  86 . EMI filters  76  filter EMI from the sensor return signals. Multiplexer  78  is controlled via a connection  90  from DSP  42  to select one of the sensor return signals for connection to input amplifier  74 . The amplified sensor return signal is converted from analog to digital by ADC  72  for application to DSP  42  at a rate sufficient to characterize the waveform as needed (i.e. 1 MHz for most applications) and to accommodate the noise environment. 
   Each of connectors  60 – 66  and connectors  80 – 86  is intended for connection with a sensor  32 . For example, connectors  60  and  80  and connectors  61  and  81  are connected in circuit with the sensors designated as S 1  and S 2 , respectively. Connectors  60  and  80  form a connector pair and a channel of RDC  30 . Connectors  61  and  81  form a connector pair and a channel of RDC  30 . Similarly, the remaining connectors  62 – 66  form connector pairs with connectors  82 – 86 , respectively, and channels of RDC  30 . 
   Two or more RDC channels can be used to interface to multiple excitation or multiple return type sensors such as linear variable differential transformers (LVDTs)/rotational variable differential transformers (RVDTs) and three wire ratiometric sensors, such as some weight/balance sensors. A receiver channel alone (without excitation) can be used to measure independently generated signals, such as a flowmeter turbine speed signal or other frequency signal sensors. 
   Seven channels are shown by way of example only. It will be appreciated by those skilled in the art that the number of channels chosen for an RDC  30  is dependent on the number of sensors and their locations in a given application as well as trade-offs, such as cost vs. throughput rate, redudancy and other considerations. 
   RDC  30  also includes a power supply  100  that has a regulator  102  to provide regulated voltages to the various components of RDC  30 . RDC  30  optionally includes discrete input/output (I/O) circuits  104  for use in providing and receiving simple discrete inputs without using up a standard RDC channel 
   RDC  30  also provides scaling control signals to DAC  52  and input amplifier  74  via connections  92  and  94 , respectively. 
   DSP  42  may be any suitable processor, known currently or in the future, and preferably is a digital signal processor that is capable of generating the sensor excitation signals and processing the sensor return signals. For example, DSP  42  may be a Texas Instruments Corporation part number TMS320LV5400. 
   DSP  42  processes discrete Fourier transform or FFT algorithms in real time to calculate the sensor parameters. DSP  42  also generates the excitation waveform by stuffing DAC  52  with look-up table values or calculated values. 
   For the majority of sensor applications, the measurement will be made for the impedance (inductive, capacitive or resistive) of the sensor with a sinusoidal excitation of a given frequency. To process the acquisition of any impedance type sensor, DFT (Discrete Fourier Transform) calculations are done using the DSP MAC (multiply-accumulate) instructions of DSP  42  to determine the impedance at the given excitation frequency. 
   Similar measurements are made on a reference element, which is a high precision resistor in order to calibrate the scaling and to define zero phase for establishing the phase of reactive impedances. 
   Referring to  FIG. 3 , RAM  46  includes a configuration program  116 , a measurement procedure  118 , a configuration data file  110 , which includes a channel assignment file  112  and a sensor configuration file  114 . Sensor configuration file  114  lists for each of a plurality of sensor types, designated as A through J, characteristics that are unique to that sensor type. For example, sensor configuration file  114  lists for sensor type A excitation signal parameters, scaling parameters and return signal characteristics. Similar characteristics would be listed for sensor types B through J. 
   Channel assignment file  112  lists an assignment of sensor type to each channel. For example, channel  60 / 80  is assigned to sensor type A. That is, channel  60 / 80  is connected to a sensor  32  of type A. Channel  61 / 81  is connected to a sensor of type B, and so on. Alternatively, as described above, two channels can be used to interface to multiple excitation or multiple return signal sensor types, or a single input channel used for non-excitation signals. 
   Configuration data  110  can be downloaded To RDC  30  from one or more of computers  26  upon power up of measurement system  20  or at any other suitable time. Alternatively, a sensor menu configuration table  114  could be programmed into ROM  44 . This would avoid downloading thereof, thus avoiding use of the bandwidth of bus  24 . 
   DSP  42  runs configuration program  116  to configure RDC  30  for the sensors types that are connected to the channels of RDC  30  based on the configuration data file  110 . When configured for the channels of RDC  30 , DSP  42  generates the desired excitation waveforms (frequency, amplitude, and wave shape), measurement circuit scaling parameters and performs discrete sampling of the sensor return signals. That is, RDC  30  provides a common circuit interface type to the sensors  32 . Additional dedicated lines  120  provide for discrete logic level signal measurements and discrete outputs for rapid response functions, such as engine overspeed shutdown or dual turboprop autofeather control. 
   DSP  42  runs measurement procedure  118  that uses a sampling procedure or time domain processing procedure to provide precision phase angle and amplitude measurements of AC signals at specific discrete frequencies relative to the sample rate. Either of these procedures makes it possible for a single processing solution to provide precision measurements over a broad range of configurable frequencies and amplitudes. The sampling procedure may be a standard Discrete Fourier Transform (DFT) process or a Fast Fourier Transform (FFT) process. The DFT and FFT signal sampling/processing techniques provide a capability to create the general purpose common interface circuit for the RDC. Although generally not a cost-effective solution for discrete measurements, an RDC channel may be configured to do so. The time domain processing procedure may be a digital filtering process or a zero crossing detection process. 
   The measurement system and method of the present invention provides multiplexed multi-channel operation to support multiple sensor technologies, including but not limited to: two or three wire proximity (inductive) sensors, two or three wire capacitive (i.e., fuel gauging), LVDTs, RVDTs, synchros, strain sensors, temperature and pressure sensors, engine speed sensors, monopole torque sensors and the like. 
   The method of the present invention provides to each of a plurality of substantially identical RDCs  30  a configuration data file that is unique to that RDC and configures each RDC based on its unique configuration data file. The method additionally runs on each RDC  30  a measurement procedure  118  based on the configuration thereof. For example, standard sampling theory methods are preferably used to determine the desired information from the sampled data. As an example, for measurement of a Honeywell proximity sensor, two separate measurements are made—the impedance when excited with a 2 KHz sinusoidal excitation at 1V RMS, and then with a 6 KHz sinusoidal excitation at 1V RMS. At one or two microsecond intervals the following occur for a period of 1 mS.
         1) a new excitation is written to excitation DAC  52 ,   2) the excitation and sensor return signal are sampled simultaneously, and   3) the samples are used to update four MAC (multiply-accumulate) sums needed to calculate the DFT of the return signal at the frequency of excitation. The four MAC sums are the sine and cosine MAC sums performed on both the excitation and the sensor return signal samples.       

   At the end of the acquisition period the DFT calculations are completed to determine the content (phase and amplitude) of the sensor signal with respect to that of a reference resistor  122  or  124  ( FIG. 2 ). The impedance is then determined by relative comparison of the phase and amplitude between the reference resistor and the sensor. The sensor impedance and diagnostic data are then stored for transmission on bus  24 . 
   The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.