Abstract:
The disclosed technology relates to a probe for use with a test and measurement instrument. The probe includes a digital multimeter or voltmeter with an analog-to-digital converter configured to measure a signal from a device under test and determine a digital measurement from the signal, a controller connected to the multimeter or voltmeter configured to receive the digital measurement from the multimeter or voltmeter, a digital communication interface connected to the controller configured to communicate with the controller, and a communication link connected to the digital communication interface and the analog signal interface to communicate with the test and measurement instrument.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 61/868,968, filed Aug. 22, 2013, entitled “ISOLATED PROBE WITH DIGITAL MULTIMETER OR DIGITAL VOLTMETER,” the disclosure of which is incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The disclosed technology relates to a probe or an accessory head for an instrument, preferably a test and measurement instrument, such as an oscilloscope, that includes a digital multimeter or a digital voltmeter that provides a reading that is galvanically isolated from earth ground. 
     BACKGROUND 
     Digital multimeters (DMM) and digital voltmeters (DMV) are commonly used in conjunction with test and measurement instruments, probes, and accessories. The test and measurement instrument may be an oscilloscope, for example. An oscilloscope provides a visual picture in time of how a circuit is performing. Traditionally, with oscilloscopes, the accuracy and resolution of a voltage measurement is limited and is typically a ground referenced measurement. DMMs and DVMs, on the other hand, can provide extremely accurate, high resolution measurements that are galvanically isolated, also known as “floating,” from earth ground. 
     Past attempts have been made to incorporate DMM and DMV measurements into oscilloscopes to obtain an accurate voltage measurement. These attempts, however, have been limited by requiring an additional set of probes to be connected to the device under test or integrating the DVM feature into the oscilloscope itself that is ground referenced and is limited in sensitivity and accuracy by the traditional oscilloscope probe connected to the oscilloscope. 
     Combining DMM-like and DMV-like measurement capabilities with a traditional oscilloscope voltage probe that is galvanically isolated from earth ground would overcome the limitations of the past and provide an easy to use solution. This would be particularly useful for users making non-ground referenced, or “floating,” voltage measurements. 
     SUMMARY 
     Certain embodiments of the disclosed technology include a probe for use with a test and measurement instrument. The probe includes a digital multimeter or voltmeter with an analog-to-digital converter configured to measure a signal from a device under test and determine a digital measurement from the signal, a controller connected to the multimeter or voltmeter configured to receive the digital measurement from the multimeter or voltmeter, a digital communication interface connected to the controller configured to communicate with the controller, and a communication link connected to the digital communication interface and the analog signal interface to communicate with the test and measurement instrument. 
     Certain other embodiments of the disclosed technology include a test and measurement system. The system includes a probe having a digital multimeter or voltmeter with an analog-to-digital converter configured to measure a signal from the device under test and determine a digital measurement from the signal, a controller connected to the multimeter or voltmeter configured to receive the digital measurement from the multimeter or voltmeter, a digital communication interface connected to the controller configured to communicate with the controller, and a communication link connected to the digital communication interface and the analog signal interface. The system also includes a second controller connected to the communication link and an oscilloscope connected to the probe through the second controller and the communication link. 
     Certain other embodiments include a method of using a probe with an oscilloscope. The method includes measuring a signal from a device under test at the probe, determining a digital measurement from the signal with a digital multimeter or voltmeter with an analog-to-digital converter located within the probe, receiving the digital measurement by a first controller within the probe, communicating the digital measurement from the first controller to a digital communication interface within the probe, and communicating the digital measurement from the digital communication interface to a second controller through a communication link. 
     The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of embodiments of the invention which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a high-level view of a test and measurement system. 
         FIG. 2  illustrates a probe according to certain embodiments of the disclosed technology. 
         FIG. 3  illustrates a probe according to other embodiments of the disclosed technology. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings, which are not necessarily to scale, like or corresponding elements of the disclosed systems and methods are denoted by the same reference numerals. 
       FIG. 1  shows a high level view of a test and measurement system using a probe  100  with a DMM or DMV  104  within the probe  100 . Initially, a signal is received from a device under test (DUT)  102  by the probe  100  and measured by DMM or DMV  104 . The measurement from the DMM or DMV  104  is then sent to a controller  106 , through a communication link  110 , which will be discussed in further detail below. Finally, the controller  106  is connected to the oscilloscope  108  to display the measurement on a display (not shown) of the oscilloscope  108 . Either a high accuracy digital measurement can be displayed on the oscilloscope or a traditional analog measurement, using a single probe. Alternately, the high accuracy measurement can be used to actively compensate the displayed analog measurement. The probe  100  may be either probe  200  or probe  300 , discussed in further detail below. 
       FIG. 2  shows the components of a probe  200 , which is ultimately connected to a test and measurement instrument, such as oscilloscope  108 , according to some embodiments of the invention. As shown in  FIG. 2 , the probe  200  includes two paths. The first path, through the DMM or DMV  104  is a high accuracy, low speed digital path. The second path, through high bandwidth circuitry  202 , is a high bandwidth path, which provides the traditional oscilloscope measurements. 
     When a signal  204  is received at the probe  200 , the signal is sensed by both the DMM or DMV  104  of the high accuracy digital path and the high bandwidth circuitry  202  of the high bandwidth path. Each path will be discussed in further detail below. 
     Starting with the high accuracy path, the signal  204  is received and processed by the DMM or DMV  104 . The DMM or DMV  104  consists of appropriate signal conditioning circuitry (not shown) followed by an analog-to-digital (ADC) converter  206 . The signal  204  goes through the signal conditioning circuitry before being converted to a digital signal via ADC  206 . The digitized measurement is then sent to controller  208 . 
     Controller  208  communicates with the ADC  206  as well as with a digital communication interface  210 . The digital communication interface  210  provides the interface between the controller  208  and controller  106  through the communication link  110 . ADC  206  sends the digitized measurement to the controller  208 . Then controller  208  sends the digitized measurement to the digital communication interface  210 . 
     Turning now to the high bandwidth path, the signal  204  of the DUT  102  goes to high bandwidth circuitry  202 . The output of the high bandwidth circuitry  202  is sent to an analog signal interface  212 , which is connected to the controller  106  through the communication link  110 . 
     Controller  106  is connected to the oscilloscope, and the digital measurement from the high accuracy digital path or the analog signal from the high bandwidth path is output to the display of the oscilloscope. The oscilloscope  108 , as will be readily understood by one skilled in the art, contains input buttons (not shown) to allow a user to indicated desired parameters for the digital or analog measurements that are displayed. 
     Controller  106  either sends an output  214  with the digital measurement to the oscilloscope  108  and/or an output  216  with the analog measurement to the oscilloscope  108 . The controller  106  can also scale and condition the output signal from the ranges and parameters inputted by the user at the oscilloscope. 
     Probes  100 - 300  allow a user to use a single probe with a DUT  102  to receive digitized high accuracy measurements through the high accuracy digital path or analog measurements through the high bandwidth path. Due to the DMM or DMV  104  being placed in the probe, and controlled directly via controller  208  and indirectly via controller  106 , the DMM or DMV  104  function of the probe is galvanically isolated from the oscilloscope and earth ground. 
     The communication link  110  can be a conductor or, preferably, an optical fiber. The communication link  110  may also be a wireless or radio frequency (RF) communication link. An optical fiber communication link provides complete galvanic isolation to the test and measurement equipment it is connected to and ultimately from earth ground. Further, increasing the length of the optical fiber communication link  110  will allow the probe  200  to be connected to higher common-mode voltages with respect to earth ground 
     In other embodiments, a probe  300  may include only a high accuracy, digital path, which is galvanically isolated from controller  106  and earth ground, as shown in  FIG. 3 . For example, in  FIG. 3 , when a signal  302  is measured from DUT  102 , the signal  302  is sensed by DMM or DMV  104 . The DMM or DMV  104  has the same functions as those discussed above with respect to  FIG. 2 . For example, when the signal  302  is sensed by DMM or DMV  104 , the signal  302  is processed by DMM or DMV  104  and ADC  206  to generate a digitized measurement. The digitized measurement is sent to the controller  208 , which communicates with the digital communication interface  210 . 
     As in the embodiment shown in  FIG. 2 , the digital communication interface  210  has two-way communication with the controller  208 , and provides all the same functions as those discussed above with respect to the embodiment shown in  FIG. 2 . Digital communication interface  210  is also connected to a communication link  110  and a controller  106 . The output from controller  106  is sent to a test and measurement instrument, such as an oscilloscope, as discussed above with respect to  FIG. 2 . 
     As will be readily understood by one skilled in the art, the probes  100 - 300  can be any type of probe, sensor, or transducer. Although the probes discussed above are shown as a standalone devices, the probes  100 - 300  can be built into other devices 
     The probes of the disclosed technology allow for complete galvanic isolation between the probe and the test equipment, such as an oscilloscope, connected to the probe. When a fiber optic communication link is used for an isolation barrier, the bridging coupling across this barrier is very small which enables high common-mode rejection from direct current (DC) to very high bandwidths to be achieved. This allows the user to make non-ground referenced measurements and eliminates the potential for circulating currents to develop forming “ground-loops” which degrade the accuracy and signal fidelity of the measurement. The probes of the disclosed technology are capable of measuring signals on top of large common-mode voltages. 
     Having described and illustrated the principles of the disclosed technology in a preferred embodiment thereof, it should be apparent that the disclosed technology can be modified in arrangement and detail without departing from such principles. We claim all modifications and variations coming within the spirit and scope of the following claims.