TABLE 108. 4 Noise Reduction Checklist Source Interconnect Response Shield enclosures Shield leads Shield Filter inputs and outputs Minimize loop area(twist leads) Filter inputs and outputs Limit bandwidth Keep signal leads near ground Limit bandwidth Separate low, high-level signals Mi Keep signal and ground leads short Low f Use single ground High f: Use multiple grounds Source: H W. Ott, Noise Reduction Techniques in Electronic Systems, 2nd ed, New York: John Wiley Sons, 1988. With permission. This network model would be added as a load to the output of the device under test in order to predict its 108.7 Summary of Noise Reduction Techniques Elimination of undesired measurement errors benefits from a systematic approach to identifying and solving noise problems. Source, interconnect, and response elements of a measurement system can be treated individ ually. Some techniques, such as shielding, are applicable to all three. Various combinations of techniques should be tried to achieve best results. There are many choices of grounding techniques that vary depending on whether elements are floating or ground-referred, and based on bandwidth. In general, multiple ground connections that create ground loops should be avoided. Difficult ground loop problems may require isolation or other techniques to interrupt the ground connection between elements. Table 108.4 summarizes a checklist of noise eduction techni 108.8 Personal Computer-Based Instruments Many instrument functions are available for interface to personal computer(PC)systems. These range from plug-in cards that reside on the PC backplane to standalone instruments that communicate with the PC over standard interfaces such as RS-232 or IEEE-488 Software to control data acquisition, analysis, and display completes the computer-based instrument. Examples of such software include Lab Windows or Lab View (National Instruments), HP VEE(Hewlett-Packard), and Testpoint(Keithley-Metrabyte). Figure 108.6 shows a block diagram of an output screen developed using Lab Windows for an acoustic measurement application.a GRAPH OF SPL CURVESK TITLE: PND MEDIUM Lmax ED3-LINE DISPLAY IGRAPH OF DATA) TEXT DISPLAY AREA: FILE NAME FIGURE 108.6 Example block diagram of a virtual instrument user interface. e 2000 by CRC Press LLC© 2000 by CRC Press LLC This network model would be added as a load to the output of the device under test in order to predict its loaded behavior. 108.7 Summary of Noise Reduction Techniques Elimination of undesired measurement errors benefits from a systematic approach to identifying and solving noise problems. Source, interconnect, and response elements of a measurement system can be treated individ￾ually. Some techniques, such as shielding, are applicable to all three.Various combinations of techniques should be tried to achieve best results. There are many choices of grounding techniques that vary depending on whether elements are floating or ground-referred, and based on bandwidth. In general, multiple ground connections that create ground loops should be avoided. Difficult ground loop problems may require isolation or other techniques to interrupt the ground connection between elements. Table 108.4 summarizes a checklist of noise reduction techniques. 108.8 Personal Computer-Based Instruments Many instrument functions are available for interface to personal computer (PC) systems. These range from plug-in cards that reside on the PC backplane to standalone instruments that communicate with the PC over standard interfaces such as RS-232 or IEEE-488. Software to control data acquisition, analysis, and display completes the computer-based instrument. Examples of such software include Lab Windows or Lab View (National Instruments), HP VEE (Hewlett-Packard), and Testpoint (Keithley-Metrabyte). Figure 108.6 shows a block diagram of an output screen developed using Lab Windows for an acoustic measurement application. A TABLE 108.4 Noise Reduction Checklist Source Interconnect Response Shield enclosures Shield leads Shield enclosures Filter inputs and outputs Minimize loop area (twist leads) Filter inputs and outputs Limit bandwidth Keep signal leads near ground Limit bandwidth Minimize loop areas Separate low-, high-level signals Minimize loop areas Keep signal and ground leads short Low f: Use single ground High f: Use multiple grounds Source: H.W. Ott, Noise Reduction Techniques in Electronic Systems, 2nd ed., New York: John Wiley & Sons, 1988. With permission. FIGURE 108.6 Example block diagram of a virtual instrument user interface