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Why are the log files difficult
to read when viewing them using Microsoft WordPad?
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Answer: Certain log files generated by Puma may be too large for notepad to read. Windows then defaults to launching the text file using WordPad instead. There are known bugs in the WordPad program that cause certain lines of the log file to be incorrectly wrapped making it very difficult to read. A freeware program Cetus CWordPad solves this problem. You can download the program here by clicking on the link below.
 CWordPad.zip (1,625KB) |
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While
running Sine, I am having timing problems with the test length and time
reported in the status box and tagged data displays.
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| Answer: Your may need to verify the proper OSCILLATOR setting for the REGIT or Tiger card that is installed in your system. There have been known timing problems with a 50MHz processor setup as a 60Mhz processor. To change this setting, open up your dld.cfg in your Puma directory and change the line "OSCILLATOR 60" to "OSCILLATOR 50". |
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• What is the cause of messages like "Attenuator Error" or "Maximum Drive Exceeded"?
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| Answer: The attenuator is used to adjust the random spectrum power level (or the random background level in Sine on Random). When the random control methods call for more power, such as in increasing the test level, the attenuator is often used to allow more voltage (range) to be output from the Dac. Once the attenuator has reached the 0 dB setting (either at max drive voltage or at the maximum output available) then the user will see the "Maximum Drive Exceeded" message. In the Sine on Random application, the user may alternately see an "Attenuator Error" message. While these alarms are generally not terminal to the test, too many of these messages may indicate that the test control accuracy is being compromised. To increase the available power level, the user may try lowering the sigma clipping level value (if the test specification allows). The available power is approximately the max drive volts (from the safety limits parameters, normally set to 12 volts) divided by the sigma clipping level. Too low of a clipping value ( i.e. less than about 2 or so) will generally cause severe random output signal distortion which causes problems in maintaining control of the random spectrum during a test. Too high a value (i.e. greater than 5-6) can cause low power output availability and "spiking" of the output random signal. Finally, note that an Attenuator Error may also be caused by a true hardware error condition. This case is normally followed by an immediate test shutdown with a related "System Error" message as well. |
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What is an SRS and how is it calculated?
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| Answer: The Shock Response Spectrum (SRS) is a composite response function which is composed of the maximum amplitude responses from a "bank" (i.e. a cascaded set) of specifically defined passband filters. These filters are usually defined based on 1/n octave center frequencies. The time domain signal is independently passed through each filter and the maximum time domain response noted. The resulting set of response amplitudes are plotted against the corresponding filter center frequency which provides the basis of the SRS plot. The definition of these passband filters essentially tries to "model" a single degree of freedom system. As such, the damping and filter center frequency must be provided to complete the filter definition. For data acquisition purposes, since the filters have a bandwidth associated with their response, data acquisition operations must provide sufficient frequency (passband) data to allow proper response of the filter. This requirement generally means that the acquisition bandwidth must exceed the highest filter center frequency by a sufficient margin to allow a proper response of the filter to be obtained. For example, if the highest filter is 1000 hertz, the acquisition should allow data with frequency content to at least 2000 hertz (actual upper limit depends on the 1/n octave resolution) to be sure the 1000 hertz SRS filter bandwidth is satisfied. In addition, since the SRS is based on a set of maximum time domain (SRS filtered) responses, the data is generally "over-sampled" to provide better time domain resolution of the filter responses. The effect of over-sampling is to lower the available upper frequency content given the same sample rate. For example, data sampled at a rate of 5120 hertz is low pass filtered by the acquisition system at 2000 hertz (standard 2.56 : 1 over-sample ratio). SRS calculations generally employ at least a 5.12 : 1 ratio which means the maximum allowable upper frequency will be reduced to 1000 hertz. For this example, one could try to calculate the 2000 hertz SRS data value, but the result would most likely be under estimated and should not be relied on for a good measurement result. |
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