Data processing: measuring – calibrating – or testing – Testing system – Including program set up
Reexamination Certificate
2000-12-11
2003-07-15
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Including program set up
C702S104000, C702S176000, C702S189000, C341S110000, C341S126000, C341S144000, C341S155000, C710S005000, C710S008000, C710S020000, C710S029000, C710S036000, C369S047200, C369S047350, C369S060010, C370S229000, C370S252000
Reexamination Certificate
active
06594612
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to measurement and data acquisition systems, and, more particularly, to a scan list format for specifying measurement and data acquisition operations.
2. Description of the Relevant Art
Scientists and engineers often use measurement systems to perform a variety of functions, including measurement of a physical phenomena or unit under test (UUT), test and analysis of physical phenomena, process monitoring and control, control of mechanical or electrical machinery, data logging, laboratory research, and analytical chemistry, to name a few examples.
A typical measurement system comprises a computer system with a measurement device or measurement hardware. The measurement device may be a computer-based instrument, a data acquisition device or board, a programmable logic device (PLD), an actuator, or other type of device for acquiring or generating data. The measurement device may be a card or board plugged into one of the I/O slots of the computer system, or a card or board plugged into a chassis, or an external device. For example, in a common measurement system configuration, the measurement hardware is coupled to the computer system via other means such as through a VXI (VME extensions for Instrumentation) bus, a PXI (PCI extensions for Instrumentation) bus, a GPIB (General Purpose Interface Bus), a serial port, parallel port, or Ethernet port of the computer system. Optionally, the measurement system includes signal conditioning devices which receive the field signals and condition the signals to be acquired.
A measurement system may also typically include transducers, sensors, actuators or other detecting (or generating) means for providing “field” electrical signals representing a process, physical phenomena, equipment being monitored or measured, etc. The field signals are provided to the measurement hardware.
The measurement hardware may be configured and controlled by measurement software executing on the computer system. The measurement software for configuring and controlling the measurement system typically comprises two portions: the device interface or driver level software, and the application software or application. The driver level software serves to interface the measurement hardware to the application. The driver level software may be supplied by the manufacturer of the measurement hardware or by some other third party software vendor. An example of measurement or DAQ driver level software is NI-DAQ from National Instruments Corporation. The application or client is typically developed by the user of the measurement system and is tailored to the particular function which the user intends the measurement system to perform. The measurement hardware manufacturer or third party software vendor sometimes supplies the application software for certain applications which are common, generic or straightforward.
Measurement systems, which may also be generally referred to as data acquisition systems, may include the process of converting a physical phenomenon (such as temperature or pressure) into an electrical signal and measuring the signal in order to extract information. PC-based measurement and data acquisition (DAQ) systems and plug-in boards are used in a wide range of applications in the laboratory, in the field, and on the manufacturing plant floor.
Typically, in a measurement or data acquisition process, analog signals are received by a digitizer, which may reside in a DAQ device or instrumentation device. The analog signals may be received from a sensor, converted to digital data (possibly after being conditioned) by an Analog-to-Digital Converter (ADC), and transmitted to a computer system for storage and/or analysis. The number of bits that the ADC uses to represent the analog signal is referred to as the resolution. The higher the resolution, the higher the number of divisions the voltage range is broken into, and therefore, the smaller the detectable voltage change. A related parameter is the range, which refers to the minimum and maximum voltage levels that the ADC can span.
A common technique for measuring several signals with a single ADC is multiplexing. A multiplexer selects and routes one channel to the ADC for digitizing, then switches to another channel and repeats. Because the same ADC is sampling many channels, the effective rate of each individual channel is reduced in proportion to the number of channels sampled in addition to time needed to switch or settle each channel.
Typically, after the analog signal is selected by the multiplexer, it is amplified by an instrumentation amplifier before being converted to a digital signal by the ADC. The amplifier must be able to track the output of the multiplexer as it switches channels, and to settle quickly to the accuracy of the ADC. Otherwise, the ADC will convert an analog signal that is still in transition from the previous channel value to the current channel value. The duration required for the amplifier to settle to a specified accuracy is called the settling time. In other words, the settling time is the time for the measurement path to come to equilibrium. This value may vary depending on filtering and user signal output impedance.
A measurement may refer to a single value returned to the user, or to multiple values returned to the user. There are typically three time attributes of a measurement: settle time, switch time, and measure time. Settle time is described above. Switch time refers to the time required for switching and configuring the measurement front end. Each switch (and configuration) constitutes a transition in the measurement process and different transitions may take different amounts of time. Measuring time refers to the time required for the ADC to digitize the signal. Increasing the measurement time can increase the resolution or precision of the measurement.
In a typical data acquisition process, a sequence of measurement specifications, referred to as scan list, is executed by the DAQ device
102
A to manage the data measurements. Each entry in the scan list typically contains parameters such as gain, mode, polarity, and trigger information, which specify the manner in which a particular measurement is to be made. A scan refers to a sequence of measurements which is repeated. A scan may specify data acquisition among several channels, e.g., Ch
0
, Ch
3
, and Ch
9
could be controlled by a single scan. The control afforded by the parameters in a typical prior art scan list is extremely limited, in that timing information must generally be set and remain constant throughout the data acquisition process. Additionally, high-level execution control mechanisms are generally not available at the level of scan list execution.
Generally, the time between the same (corresponding) measurements in different scans is fixed, e.g., the time from Ch
0
in one scan to Ch
0
in the next scan is always the same. Time between different measurements in the same scan is generally not the same, e.g., the time from Ch
0
to Ch
3
could be different than the time from Ch
3
to Ch
9
.
Poor settling time is a major problem for DAQ systems because the level of inaccuracy usually varies with gain and sampling rate. In other words, there are situations where measurements with fast and slow settling times occur in the same measurement series. Longer settling times are required if gains are switched, but there are currently no mechanisms for lengthening settling times only where needed. Because these errors occur in the analog stages of the DAQ process, no error messages may be returned to the computer when the amplifier does not settle. In typical DAQ systems, a solution is to set the settle time to the greatest value required for a particular channel gain/sample rate. Similar constraints apply to switching times between channels. In many older models of DAQ hardware, inter-channel delay has to be constant and so all switching times must be set to accommodate the slowest speed switch in the process.
Similarly, not all measurem
Desta Elias
Hoff Marc S.
Hood Jeffrey C
Meyertons Hood Kivlin Kowert & Goetzel P.C.
National Instruments Corporation
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