Abstract:
The present invention is an apparatus for detecting machine parameters including vibration, producing signal corresponding to the parameters and conditioning the signals by means of predetermined criteria such as amplitude and time criteria. Routes may be input to the analyzer with settings that govern part of the conditioning for individual machines. The predetermined criteria also may include an input limit criterion which ensures the safety of the analyzer circuitry by indicating attenuation levels for incoming signals. The analyzer is also capable of two channel analysis of input signals including a summing analysis. The analyzer has thumb operated controls for easy operation in harsh environments.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to provisional application No. 60/453,681 filed Mar. 11, 2003. 

   FIELD OF THE INVENTION 
   This invention pertains to a hand-held analyzer for detecting and analyzing machine parameters including parameters such as vibration, and particularly relates to an analyzer that produces and conditions parameter signals to increase accuracy of the parameter signals or to increase accuracy and reliability of the analysis of the parameter signals. 
   BACKGROUND OF THE INVENTION 
   Analyzers for analyzing machine parameters are used in the predictive maintenance industry to determine the health of machinery. For example, an analyzer may process vibration signals from a machine to determine mechanical conditions of the machine, such as a worn or cracked bearing race. As another example, the flux produced by an electric machine may be analyzed to determine the health of windings in the machine. While such analyzers are typically sophisticated in the types of analytical operations they perform, they are still subject to errors due to faulty interpretation of noisy signals. For example, a noisy tachometer signal might fool an analyzer, or an unexpectedly large input signal may cause errors or even failures in some analyzers. The present invention includes features to improve accuracy, stability, fault resistance and reliability in noisy and harsh industrial environments, and includes further features that improve the analytical capabilities and speed of the analyzer. 
   SUMMARY 
   The present invention provides an apparatus for efficiently identifying and analyzing concerns possibly requiring maintenance for various types of machines such as motors, pumps, fans, presses, drive trains, gear boxes, etc. It allows for complex analysis, including summation, of multiple signals representing machine characteristics through dual channels, and provides the opportunity for economy, time savings and safety through preprogrammed routes which allow the apparatus to set predetermined settings based on the machine which is next to be analyzed. The analyzer attenuation circuitry that is set or preset to optimize performance and speed and to increase instrument stability and resistance to failure. 
   In accordance with one aspect of the present invention, an analyzer is provided for monitoring a machine. A user input interface receives and transmits a user input, and an analog input receives a raw analog input signal. A conditioning circuit receives the raw analog signal and produces a conditioned analog signal based on predetermined criteria such as an input limit. In accordance with one embodiment, the conditioning circuit includes an attenuator circuit that attenuates the raw analog signal if its magnitude is too large as compared to the input limit. A data processor receives and responds to the user input to control the analyzer. For example, the data processor controls the attenuation circuit based on the predetermined criteria and performs analysis of the conditioned analog signal. An output produces an output signal corresponding to the conditioned analog signal. 
   In accordance with another aspect of the invention, the analog input include at least a tachometer input for receiving a raw tachometer signal having a magnitude and having a plurality of pulses with a cycle time corresponding to a speed of the machine. The conditioning circuit includes at least a qualifying circuit connected to the tachometer input for receiving and processing the raw tachometer signal and producing a qualified tachometer signal when the raw tachometer signal is qualified based on predetermined criteria. The output for produces an output signal corresponding in part to the qualified tachometer signal. 
   The conditioning circuit may include an amplifier gain circuit that amplifies the raw analog signal based on a preset gain stored in a memory. The user input may include a route that includes information relating to a group of machines to be analyzed. Each of the machines in the route is correlated to machine-specific preset gains which are stored in the memory. The user is prompted by the analyzer to take measurements from a particular machine, and when user inputs indicate that a machine in the route is or will be connected, the preset gains for that particular machine are taken from the route and used to set the amplifier gain. 
   In accordance with another aspect of the analyzer, the analyzer may include a second analog input and a second conditioning circuit. The second analog input receives a second raw analog signal, and the second conditioning circuit functions just as the first conditioning circuit functioned as described above; it processes the second raw analog signal and produces a second conditioned analog signal based on a second predetermined set of criteria. The second predetermined criteria include a second input limit just as the original predetermined criteria. A second selectable attenuator circuit is controlled by the data processor&#39;s implementation of the second predetermined criteria. The output in this embodiment produces an output signal based on both the conditioned analog signal and the second conditioned analog signal. In another embodiment of the analyzer, including the dual channel configuration described above, the analyzer further includes a summing circuit that produces a summation signal representing the addition of the conditioned analog signal and the second conditioned analog signal. The output signal may also be based on the summation signal. 
   The housing of the analyzer may include a user input interface with a plurality of buttons. The housing has a left gripping surface and a right gripping surface situated such that some of the buttons are thumb accessible when the analyzer is held by a user with the user&#39;s palms engaging the left and right gripping surfaces. 
   In the preferred embodiment of the analyzer, the analyzer includes a smart tachometer circuit, attenuation circuits, amplifier circuits, dual channels, summation capabilities, and thumb control. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing, as well as other objects of the present invention will be further apparent from the following detailed description of the preferred embodiment of the present invention, when taken together with the accompanying specifications and drawings, in which: 
       FIG. 1  is a block diagram representing the input, switching, conditioning channels, and data processor stages of the circuit constructed in accordance with the present invention. 
       FIG. 2  is a circuit diagram representing both the first and third identical preconditioning circuits and illustrating the input of accelerometer signals and attenuation and switching circuitry constructed in accordance with the present invention. 
       FIG. 3  is a circuit diagram representing the second preconditioning circuit and illustrating the input of a fourth channel input for various signals and a triaxial input and attenuation and switching circuitry constructed in accordance with the present invention. 
       FIG. 4  is a circuit diagram representing the tachometer input circuit and illustrating the input of tachometer and the qualifying mechanism and control constructed in accordance with the present invention. 
       FIG. 5  is a circuit diagram representing the summation and switching circuits which switch among various signals to provide the means for various types of analysis constructed in accordance with the present invention. 
       FIG. 6  is a circuit diagram representing one of the two amplification portions of the invention which amplifies the signal to various levels based on the position of four switches in accordance with the present invention. 
       FIG. 7  is a circuit diagram representing two clocks for providing timing signals to two analog to digital converters for converting two signals into digital signals which may be analyzed by the digital signal processor in accordance with the present invention. 
       FIG. 8  is a flow chart representing the relationship among the processors, the input and output devices, and the memory storage devices in accordance with the present invention. 
       FIG. 9  is a diagram of the face of the invention detailing the position and size of the various buttons on the face in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention relates primarily a method and structure for performing various functions in a data analyzer, such as a vibration data analyzer. To best understand the invention, an overview of the invention is provided followed by a more detailed discussion. 
   Referring now to the figures in which like reference characters designate like or corresponding parts throughout the several views, a block diagram is shown in figure one illustrating the input system  22  for a data analyzer, such as a vibration data analyzer. The system  22  includes a first input preconditioning circuit  24  configured to receive an accelerometer signal through the acceleration input  32  or an independently powered input signal through the volts input  34 . The accelerometer input  32  provides power to a sensor such as an accelerometer, whereas the volts input is a passive input that receives an input signal but does not power it. 
   A second input preconditioning circuit  26  includes a triaxial input  38  and a fourth channel input  36 . The triaxial input  38  is adapted for connecting to a triaxial sensor such as a triaxial accelerometer that produces a sensor signal corresponding to acceleration in the three different directions, such as X, Y, and Z directions. The fourth channel input  36  receives a signal corresponding to a fourth parameter in addition to the signals corresponding to the three different directions. For example, the fourth channel input  36  may receive a torque vibration signal, or a signal corresponding to linear vibration at a different measurement location, other than the location of the triaxial sensor. As shown in this preferred embodiment, the fourth channel input  36  is a powered input that may be used to power and receive a signal from an accelerometer. Certain types of balancing techniques require the use of four accelerometers and, thus, having a fourth accelerometer input provides the ability to perform this type of balancing technique, as well as other analyzing techniques requiring four powered inputs. 
   A third input preconditioning circuit  28  is provided to power and receive a sensor signal, such as an accelerometer signal, on an accelerometer input  40 , and is configured to receive another self powered sensor signal on the volts input  42 . Preconditioning circuit  28  is identical to preconditioning circuit  24 . A tachometer input preconditioning circuit  30  is also provided and is configured to receive a tachometer sensor signal on the tachometer input  44 . 
   The signals may be provided to the preconditioning of circuits  24 ,  26 ,  28  and  30  through a variety of connectors, preferably a plug system whereby various sensors are plugged into sockets associated with the preconditioning circuits. Each individual preconditioning circuit may be associated with more than one socket, or a single socket may be configured to provide input signals to more than one preconditioning circuit or all of the preconditioning circuits. 
   The preconditioning circuits  24 ,  26 ,  28  and  30  are connected by lines  46 ,  48 ,  50  and  52  to a master switch  54  that performs switching, buffering, summing and amplifying functions. It will be understood that a single line may represent multiple lines as required for a particular circuit. For example line  48  represents multiple lines so that the inputs appearing on lines  36  and  38  may both be supplied to the master switch  54 . Signals that are applied to the master switch  54  are conditioned and then supplied through lines  56  and  58  to first and second conditioning channels  60  and  62 . The conditioning channels  60  and  62  may amplify, demodulate, envelope, integrate, etc. the received signals as desired by the user and provide conditioned output signals on lines  64  and  66  to a data processor  68 , that is preferably a digital signal processor, and is most preferably a data processor having a model number DSP56301 manufactured by Motorola. The output of the data processor  68  is provided on line  69 , which is preferably a parallel bus. 
   Referring now to  FIG. 2 , a preconditioning circuit  80  is shown that corresponds to both preconditioning circuits  24  and  28 . Input line  82  corresponds to the acceleration inputs  32  and  40  shown in figure one. While input line  82  is represented by a single line in this figure, it will be understood to represent one or more lines as needed for a particular accelerometer or other sensor. The input signal on line  82  is provided to a resistor divider  86  which places the input signal on a raw input line  85  which connects the input signal directly to the switch  102  shown in figure two. The input signal on line  82  is also applied through switch  88  to a parallel set of attenuators  96 ,  98  and  100  that attenuate the signal by a factor of one, one third, and one tenth, respectively. Each of the attenuators  96 ,  98  and  100  have an output applied to a switch  102 . The switch  102  may connect output  104  to one of the attenuators and  96 ,  98  and  100  or to lines  85 ,  113 ,  117  and  103 . The signal appearing on line  85  is the raw accelerometer input signal after it has been attenuated by the resistor divider  86 . The signals appearing on lines  113  and  117  are described hereafter. Line  103  is connected to receive the signal from the third input preconditioning circuit  28 . 
   With continuing reference to  FIG. 2 , a second input line  84  corresponds to the voltage input  34 . The signal appearing on line  84  passes through an attenuator  90  that attenuates the signal by a factor of one half and applies its output to a switch  92 . The attenuator  90  also functions as a buffer to provide a high impedance input to avoid having any adverse affect on the circuit or a device that is providing the input signal. When the switch  92  is in the position shown in  FIG. 2 , it applies a DC coupled signal directly to the switch  88 . When the switch  92  is turned off, an AC coupled signal is applied through capacitor  94  to the input of switch  88 . The data processor  68  controls the position of when and  88  so that it can select either a DC or an AC coupled input signal from line  84 . 
   From the above, it is appreciated that the data processor  68  may select attenuated versions of the signals appearing on lines  82  and  84 , or the raw signals appearing on lines  85 ,  113 , or  117  by controlling the switches  102 ,  88  and  92 . 
   Referring to  FIG. 3 , the circuit  110  is a more detailed block diagram of the second input preconditioning circuit  26 . Line  112  corresponds to the fourth channel input  36  and line  114  corresponds to the triaxial input  38 . The signal on line  112  is applied through a resistor divider and appears on line  113 , which is connected to the switch  102  previously described. This signal is also applied through a capacitor to the inputs of a switch  116  and attenuator  118 . When the switch  116  is in the position shown in  FIG. 3 , an AC coupled signal appears on line  124  without attenuation and is further applied to the circuits. When the switch  116  is connected to the output of attenuator  118 , the input signal from line  112  is attenuated by a factor of ten, and the attenuated signal appears on line  124 . The triaxial signal appearing on line  114  is applied through a capacitor to an attenuator  120  and a switch  122 , which correspond to the attenuator  118  and switch  116  discussed above. Thus, line  126  receives either an AC coupled triaxial signal from line  114  or it receives the same signal attenuated by a factor of ten. 
   A tachometer input circuit  138  is shown in  FIG. 4 , and a tachometer signal is applied on the input line  140  that is connected to a high impedance input provided by an adjustable gain stage  142 . The output of stage  142  is applied through line  144  to an adjustable discriminator  148  and through line  146  it supplies a raw tachometer signal to other parts of the circuit. The output of the adjustable discriminator  148  is applied to a tachometer data processor  150  that controls the operation of the adjustable discriminator  148 . The data processor  150  is connected by line  152  to the data processor  68 . Preferably line  152  is a serial data bus enabling communications to and from the data processor  68 . As will be described hereinafter in greater detail, the data processor  150  controls the adjustable discriminator  148  to set thresholds and conditions that determine when and if a tachometer pulse is detected and reported to the data processor  68 . 
   The circuits described in  FIGS. 2–4  provide inputs to the master switch  160 . The output of circuit  80  ( FIG. 2 ) appears on line  104  which is connected to line  162  ( FIG. 5 ). Likewise, referring to  FIG. 3 , the outputs on lines  124  and  126  are applied to lines  164  and  166  in  FIG. 5 . Line  168  is connected to receive the output from the third input circuit  28 , which is identical to the circuit  80  described in relation to  FIG. 2 . Line  146  appears in both  FIGS. 4 and 5  and shows the connection between the tachometer input circuit  138  and switch  182  (part of the master switch  54 ). 
   The input lines  162 – 168  are applied to the input of buffers  170 ,  172 ,  174 ,  178 , whose output is applied through a parallel connection to both switches  180  and  182 . The switches  180  and  182  may connect to any of the input signals produced by the circuits described in  FIGS. 1–4 . In addition, switch  182  may connect to line  146  that carries the raw buffered tachometer signal. The output lines  184  and  186  in  FIG. 5  correspond to the output lines  56  and  58  shown in figure one, and each of the output lines carries one of the input signals to the switches  180  and  182 . 
   The output lines  184  and  186  are connected to the first and second conditioning channels  60  and  62 . Each of conditioning channels  60  and  62  are identical to the circuit  190  shown in  FIG. 6 . Line  192  in  FIG. 6  represents either of the lines  184  and  186 . The input line  192  is connected to a high pass filter  194  and an overload detect circuit  196 . If an overload is detected by circuit  196 , an overload indication is provided to the data processor  68  by communication lines that are not shown. The output of the high pass filter  194  is connected to a switch  198  that is controlled by the data processor  68 . The switch  198  connects either to the output of the high pass filter  194  or connects to a line  200  that bypasses the high pass filter  194 . Thus, the switch  198  operating under the control of the data processor  68  is connected to either a filtered or and unfiltered input signal. 
   The output of switch  198  is applied through an amplifier  202  having a gain of one and functioning primarily as a buffer. The output of amplifier  202  is applied to the input of an integrator  204  and a switch  206 . The output of the integrator  204  is applied to the input of an integrator  212  or the input of switch  209 . The outputs of switch  206 , switch  209 , and integrator  210  are applied to a single input of an amplifier  212  having a gain of one and functioning as a buffer. 
   The data processor  68  controls the operation of switches  206  and  209  such that the input signal is either not integrated, or is integrated once, or is integrated twice. When an accelerometer signal is provided as an input, the signal that is not integrated represents an acceleration. The signal that is integrated once represents a velocity and the signal that is integrated twice represents displacement or distance. The output of the amplifier  212  is provided to a summer  214  whose other input is connected to a DC offset circuit  218 . The circuit  218  provides a signal that subtracts any DC component from the signal appearing at the output of the amplifier  212 . Again, the DC offset circuit  218  communicates with and is controlled by the data processor  68 . 
   The output of the summer  214  is applied to a variable amplifier  216 , whose gain is controlled by the data processor  68 . The output of amplifier  216  is applied to the inputs of amplifier  220  having a gain of twelve and a switch  222  that bypasses the amplifier  220 . The outputs of the parallel amplifier  220  and switch  222  are applied to the input of a low pass filter  224  and another overload detect circuit  226 . When the switch  222  is in the “Off” position as shown in  FIG. 6 , gain on amp  240  is set to 12. If the switch  222  is switched “On”, amplifier  220  gain is set to 1. The gain of the amplifier  220  and the position of switch  222  is controlled by the data processor  68 . The overload detect circuit  226  determines whether the signal appearing at the input of the low pass filter  224  exceeds a threshold indicating improper operation of the circuit. If the threshold is exceeded, the detector circuit  226  reports the malfunction to the data processor  68 . 
   Referring again to  FIGS. 1 ,  6  and  7  there are first and second conditioning channels  60  and  62 , each being identical to the circuit  190  shown in  FIG. 6 . The output of the first conditioning channel  60  (line  64  in  FIG. 1  and line  228  in  FIG. 6 ) is applied through line  232  to an analog to digital converter, ADC  236 . The output of the second conditioning circuit  62  (line at  66  in figure one and line  228  in the  FIG. 6 ) is applied through line  234  to the ADC  238 . The ADC  236  which is part of the first conditioning channel  60  receives a clock signal through switch  244  that is connected to either a first clock  240  or a second clock  242 . The second clock  242  is always applied to the ADC  238 . Thus, the ADCs  236  and  238  receive either the same clock signal or different clock signals depending upon the position of the switch  244  which is controlled by the data processor  68 . 
   The data processor&#39;s  68  is also connected through line  152  (preferably a data bus) to communicate with the tachometer processor  150 . Thus the data processor  68  receives a tachometer signal that has already been processed by the processor  150  to improve reliability. 
   Referring now to  FIG. 8 , an overview of the analyzer  245  of the invention is shown. The data processor  68  is connected through line  69  (a data bus) to a data processor  250 , preferably a 32 bit microprocessor. In the preferred embodiment, the data processor  68  substantially simultaneously processes the signals produced by the first and second conditioning channels  60  and  62 . Each of the ADCs  236  and  238  are preferably Sigma Delta converters manufactured by Analog Devices and have a maximum output rate of 234375 samples per second (3750000 bits per second), but as configured in this particular circuit the ADCs produce a maximum output bit rate of 3276800 bits per second (204800 samples per second). The data processor has the capacity to receive and simultaneously process two signals each having a bit rate of 3276800 bits per second (204800 samples per second). Because of the speed of the data processor  68 , it is performing substantially parallel processing of the two signals appearing on lines  64  and  66 , even though portions of each signal are being processed sequentially (serially) by the data processor  68 . By the use of memory, such as buffers, the data processor  68  is capable of operating on two signals sequentially to achieve parallel processing of the two signals. 
   After the input signals have been processed by the data processor  68 , the processed signals are provided through line  69  to the microprocessor  250 . Memory  258 , preferably both RAM and ROM, is connected to the microprocessor  250 , and additional memory is provided by a PCMCIA card  256  that is also connected to the microprocessor  250 . For providing communication to outside computers, communications ports  260  are interfaced with the microprocessor  250  and may include parallel and serial communications ports, such as an RS-232 Port, or a USB port. Commands and other instructions are input through a keypad  262  that is interfaced with the microprocessor  250 , and information is provided to a user by the microprocessor  250  issuing display signals that are applied to a display driver  252  producing images on the display  254 . 
   Operation 
   Referring to  FIG. 8 , the operation of the instrument is initiated by depressing a power button on the keypad  262 . Then, operation of the instrument is controlled by the user inputing instructions through the keypad  262 . The microprocessor  250  responds to the user inputs by providing information back to the user through display  254 . In addition, the microprocessor  250  sends commands to the data processor  68  instructing it to receive and process signals as required by the user. Typically, one or more information signals (input signals) are received by the data processor  68  and processed. For example, the data processor  68  may receive two acceleration signal inputs corresponding to measured vibration and a tachometer signal input corresponding to rotation of a machine. The acceleration signal inputs are typically processed by the circuit  190 , such as by integrating the acceleration signal once or twice to produce velocity or displacement signals. Also, the data processor may perform transform functions on the signals, such as Fourier transform functions. 
   Referring to  FIG. 4 , an intelligent tachometer input circuit  138  is illustrated. Included is a data processor  150  operating under the control of the data processor  68 . The data processor  150  sets and maintains conditions for qualifying a signal as a proper tachometer pulse. Often the tachometer signals are dirty, meaning they have a number of noise attributes that may fool a simple circuit into believing that a tachometer pulse represents multiple pulses or no pulses. To combat this problem, the data processor  150  under the control of the data processor  68  sets a threshold amplitude for a qualified tachometer pulse. 
   The threshold amplitude is set in different ways. In a manual mode, the threshold amplitude is set by the user. In response to instructions from the user, the tachometer signal is displayed and frozen for the user on display  254 . The user then inputs a threshold amplitude based on the frozen tachometer signals shown on the display. Typically, a user will select an amplitude that is well above the noise floor, but well below the peak amplitude of the tachometer pulse. 
   In an automatic mode, the data processor  150  automatically sets the tachometer threshold by determining the peak amplitude of the input signal over a predetermined period of time and sets the threshold at a percentage of the average peak amplitude. Preferably, this threshold may be set at 80 percent of the average peak amplitude measured over 10 machine cycles (10 tachometer pulses). 
   A tachometer pulse may also have multiple pulses within the individual tachometer pulse, and there may be valleys within a single tachometer pulse that fall below a threshold set for the tachometer pulse. Thus, additional conditions are imposed to prevent the system from interpreting a single tachometer pulse as multiple tachometer pulses. One such condition is a time limitation between tachometer pulses. The data processor  150  is programmed to disregard a tachometer pulse that meets the threshold amplitude condition, but occurs within a preset time limit of a previous tachometer pulse. 
   This time limit may be sent in a number of ways. First, in a manual setting, the user is allowed to input a time limit. The user&#39;s input of a time limit is checked against known information programmed into the analyzer. For example, when the analyzer is being used to receive data from a particular machine on a route, the analyzer will know the nominal operating speed of the machine. The nominal operating speed of the machine will be information that is contained within the route is therefore available to the analyzer. Based on that nominal operating speed, the analyzer will make a judgment as to whether the user&#39;s input of a time limit is reasonable. Preferably, the data processor  150  will compare the user&#39;s time limit to a calculated upper and lower limit. Both of these limits will be calculated as a percentage of a machine cycle, the time required for the machine to rotate once. If operating properly, the tachometer will produce one tachometer pulse per cycle. Thus, the upper limit is calculated as a large percentage of the machine cycle time. For example, the upper limit may be 80 percent of a nominal cycle time. The lower limit is a small percentage of the cycle time, for example 10% of the cycle time. If the user&#39;s time limit is greater than the upper limit or less than the lower limit, a warning message is provided to the user, but the user&#39;s time limit is followed. 
   In one automatic mode of operation, the data processor  150  automatically sets the time limit at 50% of one cycle time. To begin operation, data processor  150  sets the time limit at 50% of the nominal cycle time of a machine. Then, as tachometer pulses are detected, an actual cycle time of the machine is calculated, and the time limit is set at a percentage of the actual cycle time of the machine, such as 50% of the actual cycle time. The user also has the option of setting the initial time limit and allowing the data processor  150  to reset the time limit based on the actual measured machine cycle time. The default percentage for the time limit is 50%, but the user may change the percentage used by the data processor to establish the time limit for the tachometer. For example, a user may wish to instruct the microprocessor  250  to set a time limit of 40% of one cycle time. By each of the above described modes of operation, the tachometer processor  150  imposes both a threshold amplitude and a threshold time limit upon a candidate tachometer pulse to qualify it as an actual tachometer pulse. By imposing these conditions, a more reliable tachometer pulse is achieved. 
   In the specific embodiment shown as an example in  FIG. 4 , the data processor  150  applies a signal through line  154  to a discriminator  148 . The signal on line  154  represents the threshold amplitude that the pulse from the tachometer must exceed. If the tachometer pulse is less than the threshold amplitude on line  154 , the discriminator  148  does not generate a pulse at its output even when a pulse is received on the input  144 . However, when the pulse on line  144  exceeds the amplitude of the signal on line  154 , the adjustable discriminator  148  produces an output that is applied to the data processor  150 . The data processor then determines whether a time limit has been met. That is, the data processor  150  determines whether sufficient time has passed since the previous tachometer pulse. If the answer is yes, the data processor  150  will report a tachometer pulse on line  152  to the data processor  68 . If desired, both the amplitude threshold and the time limit threshold for the tachometer pulse may be implemented by analog circuitry. Likewise, the data processor  150  could digitally apply both the amplitude threshold and time limit as qualifying conditions. However, it is preferred to apply the amplitude threshold by analog circuitry and apply the time limit by digital circuitry. 
   Another factor influencing the accuracy of a signal analyzer is the amplitude of the signal received from a sensor. To provide accurate results, prior analyzers have an automatic gain control feature that will adjust the gain of amplifiers in the circuit to accommodate input signals of different amplitudes and thereby maximize the sensitivity and accuracy of the analyzer. However, the automatic gain control feature requires time to analyze the input signals and set the gain of various amplifiers. In the present invention, a route of machines is downloaded into the microprocessor  250 . The route identifies a number of machines from which data will be obtained. For each machine on the route, a preset gain is recorded. Thus, when an operator provides input signals through the keypad  262  indicating that a particular machine on a route will be tested, the microprocessor  250  instructs the data processor  68  to set the gains of various amplifiers based on the preset to gain stored in the microprocessor  250  as part of the route. Thus, referring to  FIG. 6 , the data processor  68  sets the gain of the amplifier  216  and sets the switch  222  either on or off to determine whether amplifier  220  will be included in the circuit. In addition, referring to  FIG. 2 , the data processor  68  issues signals to the switch  102  to select one of the attenuators  96 ,  98  and  100 , if that particular input circuit  80  is being used. Likewise, switches  116  and  122  are switched to a desired position based on the preset gain and the attenuators  118  and  120  are either selected or excluded from the circuit for the initial measurements. 
   Once the microprocessor  250  and data processor  68  have preset the gains of the various amplifiers and attenuators, the instrument immediately begins to acquire signals and process the signals according to the preset information in the route for a particular measuring point and a particular machine. As part of that analysis, the input signal will be qualified. That is, the signal will be analyzed to determine whether the signal amplitudes are within a preset range that will produce accurate data. If the input signal qualifies, the data processor  68  will continue to process the data normally. If the input signal does not qualify, the data processor  68  will disregard the input data, discontinue its analysis, and perform an auto ranging function whereby the amplifiers and attenuators are reset to achieve an acceptable or qualified signal that will produce accurate data. If auto ranging is required for a particular point on a particular machine, the new gain settings determined by the auto ranging process will be saved in the route data as the new preset gain for the particular measuring point and machine in question. 
   Referring again to  FIGS. 2 and 3 , it is noted that three attenuators  96 ,  98  and  100  are provided in circuit  80  for the purpose of attenuating large amplitude input signals. One problem associated with signal analyzers is the larger variability of the input signals. Depending upon the sensor, an input signal may be sufficiently large to saturate the instrument and cause inaccurate measurements or damage to the instrument. Thus, in the present invention the input circuits all include optional attenuators in the early stages of the input circuits to maximize efficient and accurate measurements and protect the instrument itself. In circuit  80  of  FIG. 2 , the voltage input  84  includes an attenuator  90  that is included in every circuit for additional protection against excessively large input signals. In  FIG. 3 , attenuator  120  is provided for the triaxial input  114  and attenuator  118  is provided for the fourth channel input at line  112 . One or more of these attenuators may be selected by the data processor  68  as needed for a particular measuring, a particular machine or a particular sensor. 
   The two channel operation of the analyzer may best be understood by reference to  FIGS. 5 ,  6  and  7 . Referring to  FIG. 5 , it is appreciated that the input signals appearing on lines  162 ,  164 ,  166  and  168  may be applied to either or both of the two channels represented by lines  184  and  186 . Thus the same signal or different signals may be applied to lines  184  and  186 . 
   Referring to  FIG. 7 , it may be appreciated that one channel of operation is represented by ADC  236  and the other channel is represented by ADC  238 . The ADC  236  and ADC  238  may receive the same clock signal from clock  242 , or clock  242  may be connected only to the ADC  238  and clock  240  may be connected to the ADC  236 . Considering the clock arrangement in  FIG. 7  and the switching arrangement of  FIG. 5 , the flexible analysis possible with this circuitry is best appreciated. If the same signal is applied to both channels, it is likely that different analysis of the same signal is required. Thus, different clock signals may be necessary or desirable at ADC  236  and ADC  238 . In such case, switch  244  is positioned as shown in  FIG. 7  so that ADC  236  receives a clock signal from clock  240 . At the same time, ADC  238  receives a different clock signal from clock  242 . Thus, under the control of the data processor  68 , each ADC may be operated at very different clock speeds. This capability is particularly advantageous for providing fast multiple analysis of the same signal. 
   On the other hand, in other applications it is important to perform the same analysis on two different signals. In such case, it is desirable to have the same clock signal applied to both ADC  236  and ADC  238 . By switching the switch  244  to the opposite position from that shown in  FIG. 7 , both ADC  236  and ADC  238  are connected to clock  242  and ADC  236  is disconnected from clock  240 . Thus, two different input signals may be analyzed with essentially identical input channels. Of course, it is also possible to provide the same clock signal to both channels when identical signals appear on both channels, and it is possible to provide different clock signals to the different channels when the different signals appear in each channel. In short, the switching and clocking circuitry provide a high level of flexibility in the analog input channels. Thus, a single input signal may be processed faster with a two channel operation, or different signals may be processed simultaneously in an identical manner. 
   Referring again to  FIG. 5 , a particularly convenient aspect of the invention is illustrated. A summing circuit  176  is connected to the output buffer  178  and is therefore connected to receive an input signal provided on line  168  the other input of the summing circuit  176  is connected to the output of buffer  170  and therefore receives input signal on line  162 . Lines  162  and  168  are connected to different input circuits each of which is identical to the circuit  80  illustrated in  FIG. 2 . Thus, for example, the summing circuit  176  may receive two acceleration signals from the two different accelerometers. The output of the summing circuit  176  is applied to switch  182 , and both of the two input signals to the summing circuit  176  are applied to the switch  180 . Thus, by appropriately controlling and switching the two switches  180  and  182 , the sum of two input signals may be applied to line  186  and either of the two input signals may be applied to line  184 . Thus, for example, the signals appearing on lines  162  and  168  may be summed and applied to line  186 , and the input signal appearing on line  162  may be applied to line  184 . 
   In the analysis of signals, it is often advantageous to compare the sum of two signals to one of the signals. In known prior art devices, the setup required to perform such analysis is cumbersome. In the analyzer of the present invention, the setup for this type of an analysis is simple and can be automatic. In the preferred embodiment, a route is downloaded into the analyzer, and the route may specify this particular measurement. When this particular measurement is required at a particular measurement point in the route, the data processor  68  automatically positions the switches  180  and  182  to place the sum of two input signals on line  186  and one of the two input signals on line  184 . Thus, this type of analysis may be performed automatically without any cumbersome setup. In addition, the user may instruct the instrument to configure itself for this type of analysis by simply inputting commands through the keypad  262 . 
   Referring now to  FIG. 9 , the interface between the user and the analyzer  245  is described. In  FIG. 9 , a face panel  300  is shown which includes a plurality of buttons, such as power button  302 , positioned around a display  303 . Since the analyzer  300  is used in very harsh conditions, such as factories, refineries, drilling platforms and power plants, the input for the analyzer must be extremely rugged. In this case, the display  303  is a ruggedized LCD display and all of the buttons, such as power button  302 , are covered by a flexible membrane  305  that extends across all of the button area, which includes all of the area visible in  FIG. 9  excluding the display  303 . Thus, the membrane  305  seals and protects the entire button area from penetration by solids, liquids and gases such as dust, oil, and water vapor. 
   Enter buttons  304  and  306  are positioned in the upper right-hand corner and upper left-hand corner of the face panel  300 , respectively. Below the enter button  304  is a row of function buttons  308 , and below the enter button  306 , there is a row of function buttons  310 . In the lower right-hand and lower left-hand corners, alternate buttons  312  and  314  are provided. Buttons  304 – 314  are the most used buttons on the face panel  300  and are positioned and configured to be operated by the thumbs of the user. Thus, the buttons are almost as large as a typical thumb, and are separated by relatively large distances so that it is difficult to push two buttons at one time with a thumb. In addition, each button is defined by a raised perimeter represented by the lines defining the periphery of each button. This raised perimeter provides a distinct feel to the button and allows the user to center his or her thumbs in the center of the button. The raised perimeter of each button is sufficiently large that the perimeter can be felt through most work gloves and most protective gloves. Thus, the size and shape of the buttons provide a distinctive tactile feedback to the user. 
   By positioning the buttons  304 – 314  next to the left and right edges of the face panel  300 , the analyzer  245  may be conveniently held between the palms of the user&#39;s hand and the buttons may be freely manipulated by the thumbs. As the buttons are depressed, different screens appear on the screen  303  and information is provided next to the buttons by information blocks  332 . The blocks  332  typically inform the user as to the operation that would be performed if a function button  308  or  310  were depressed. After a button is depressed, the screen changes and the information blocks  332  also change. Thus, with each new screen shown on the display  303 , the function of all the buttons  308 – 310  may change. In addition, the function button  332  may assume a different function, if either of the alternate buttons  312  or  314  are depressed. 
   Two alternate buttons  312  and  314  are provided so that either hand can push an alternate button. Thus if the user wishes to push one of the left-hand function buttons  310 , and further desires to use the alternate function of that button, the user will depress the right-hand alternate button  312  and use his left hand to push one of the buttons  310 . Likewise, if an alternative function of one of the right-hand buttons  308  is desired, the left hand depresses the alternate button  314  and the right hand depresses one of the right-hand buttons  308 . When either of the alternate buttons  312  or  314  is depressed, the information blocks  332  change to display information as to the alternate function of the buttons  308  and  310 . 
   The row of buttons  316 – 326  along the bottom of the face panel  300  are typically less used than the other buttons, but they are also conveniently located along an edge so that they too may be operated by a thumb, if desired. Thus, a user could hold the analyzer  245  with his left hand along the left side of the face panel  300  and his right hand along the bottom side of the panel  300 . This configuration also provides the user with easy access to the buttons with his or her thumbs. Button  316  is a help button which accesses the help features of the analyzer, and button  318  is a home button which takes the user back to the main home page. Buttons  320  are up and down buttons and buttons  322  provide left and right functions. By use of these buttons, the user may move between displays and display positions in up, down, left and right movements. Button  324  is a back button that a user may use to access the previous screen, and button  326  is a reset button that is used to reset the analyzer  245  and restart the process. Two indicator lights  328  and  330  are provided to indicate the status of the analyzer  245 .