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SigLab Hardware Questions
How good is SigLab's front end?
SigLab is a lab-quality measurement system with outstanding front-end signal conditioning, including programmable gain, offset, coupling, overload detection. The advanced signal conditioning and two internal fixed-point DSP processors provide:
- >90dB spurious free dynamic range
- >90dB linear-phase alias protection at all 13 user-selectable measurement bandwidths
- Frequency Translation (zoom) capabilities for narrow band measurements
For complete details, browse the SigLab Product Details Page and Select "SigLab Hardware". From there, if more information is desired, you can download a complete "SigLab Hardware Specification".
What sampling rates does SigLab use?
Each SigLab model can sample at 13 different sample rates:
- For models 20-22 and 20-42, these sample rates are 51.2 kHz, 25.6 kHz, 12.8 kHz, 5.12 kHz, 2.56 kHz, 1.28 kHz, 512 Hz, 256 Hz, 128 Hz, 51.2 Hz, 25.6 Hz, 12.8 Hz, and 5.12 Hz.
- For model 50-21, these sample rates are 128 kHz, 51.2 kHz, 25.6 kHz, 12.8 kHz, 5.12 kHz, 2.56 kHz, 1.28 kHz, 512 Hz, 256 Hz, 128 Hz, 51.2 Hz, 25.6 Hz, and 12.8 Hz.
I'm not familiar with MATLAB. Is that going to be a problem with using your product?
SigLab is an external dynamic signal and system analyzer that interfaces to a host PC running MATLAB via a SCSI bus. MATLAB sends measurement setup and control commands to SigLab and SigLab returns the results directly to MATLAB. As a user unfamiliar with MATLAB you can set up, control and view in real-time all measurements using simple and intuitive point and click GUIs ready to run right out of the box. No programming or experience with MATLAB is required. A user's manual and extensive on-line help is always available as well.
The test equipment we use has to meet certain emissions, susceptibility, and static discharge standards. Does SigLab carry the CE Mark?
All SigLab hardware has CE Mark - Class A certification.
How can I upgrade SigLab's memory?
By using overnight shipping we typically provide a 3 day turn-around for option upgrades. Since memory upgrade requires opening up the SigLab chassis and removing the "daughter board" from the "mother board" to gain access to the memory sockets, we encourage that you return the unit for us to install the upgraded memory. However, if this is not feasible, a detailed set of instructions are provided in the file upgrade.txt, which you can download and print from our FTP site. To download it now, click here.
How can I interrogate the SigLab to find out its current configuration and current version information?
Type: sigstat at the MATLAB prompt. A dialog box will appear with this information.
Note: In versions of SigLab software earlier than v2.13, sigstat was called bug.
Are SigLab's inputs time synchronized? What about SigLab's outputs?
SigLab's inputs are time synchronized. There is no channel multiplexing.
In general, SigLab's function outputs are not time synchronized. The output channels function independently of each other. However, there are two exceptions to this rule:
- If both channels 1 and 2 are generating sine waves, a phase angle can be defined.
- User defined (arb) outputs are time synchronized within each SigLab module.
Does using MATLAB limit your data acquisition and processing speed?
First, virtually all the 'real-time' processing is done in the SigLab hardware, remember there are 3 DSP chips busily churning away! MATLAB is used primarily for human interface such as graphic display, controls, or optional post-processing of measurements made by SigLab.
As to customized real-time signal analysis, the real-time processing power of MATLAB is surprisingly good especially on today's processors. Without missing a sample, the SigLab/MATLAB combination can acquire blocks of data at 12800 Hz, process with an 80th order low-pass FIR decimating filter, and then plot the filtered results. This benchmark was performed on a Pentium 90 MHz machine. We have an application note entitled, "Real-Time Processing Within MATLAB" addressing this subject.
The SigLab/MATLAB combination can average 100 different 1024 point windowed FFTs records while displaying the intermediate results (both time and frequency domain) in about 4.5 seconds. The real bottleneck to this benchmark is the display process since the results must be sent to update the display. MATLAB is very efficient in performing the few required vector oriented computations. Additionally, the SCSI bus is very efficient in transferring blocks of data, which is a real advantage of the SCSI interface. Without displaying the intermediate results, each 1024 point FFT takes about 10 milli-seconds.
What kind of ADCs and DACs is SigLab using?
SigLab is using Crystal Semiconductor sigma-delta ADCs and DACs. These converters are excellent with respect to dynamic specifications such as noise, distortion, alias suppression, and passband flatness. In short, they are ideal for analyzing dynamic signals and systems.
What kind of DSPs is SigLab using?
SigLab uses two fixed point DSP processors for real time digital processing and filtering of the input and output channels. This real-time filtering provides full anti-aliasing at all 13 user-selected bandwidths as well as the frequency translation (zoom) capabilities required for narrow band measurements. A floating point TMS320C31 DSP performs all dynamic signal/systems analysis including FFT, windowing, cross and auto spectrum and coherence computations. The C31 also manages the SCSI interface and responds to commands from - and returns measurement results to - MATLAB on the host PC.
Why does SigLab use additional anti-aliasing filters when sigma-delta converters already have a built-in AA filter?
It is true that sigma-delta converters have a built-in AA filter. But, even sigma-delta converters require an analog AA filter ahead of them. SigLab uses a fourth order quasi-elliptic filter with excellent phase linearity over the 50 kHz analysis bandwidth. Sub-optimal hardware such as the typical 'add-in DAQ' boards will use a trivial RC filter or (at worst) no filtering at all.
However, the analog AA filter and the intrinsic filtering provided by the converter, only protects to the maximum bandwidth, 50 kHz. When a lower bandwidth or frequency translation is selected, additional AA protection is required. The fixed-point DSP processor following the converter applies the real-time digital filtering required to assure >90dB AA protection at all 12 selectable bandwidths below 50 kHz.
What do the status messages displayed SigLab's front panel mean?
- The typical displays include:
- OK - all is well
- T3,4,5 - SigLab's SCSI terminator is enabled
- C1,3,5 - In a multi-box (multiple SigLabs linked) this indicates the 1st channel in the box
- dc - SigLab is being powered from its internal NiCad battery
- ac - SigLab is being powered from the back panel ac power input
Other messages are for factory diagnostic and debugging purposes.
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© Copyright 2002 Spectral Dynamics Inc.
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