EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: magicsmoke on May 02, 2015, 04:17:16 am
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I am looking for an inexpensive dynamic signal analyzer if such a thing exists for a graduate lab course on control implementation that I am planning. The lab takes control theory concepts and applies them in a hands on manner using DC motor motion control as the vehicle for exploring control theory. For many parts of the lab the students will need to measure transfer functions, determine the magnitude of signals, etc. When I took a similar course I believe we used HP 35665A 2-Channel DC to 102.4 kHz Dual Channel Dynamic Signal Analyzers which are now obsolete. Almost all spectrum analyzers I have found do not go to low enough frequencies. I need an operational frequency span which approaches DC on the low side, has multiple source modes such as random noise, periodic chirp etc, and can compute transfer functions, and display the coherence.
Keysight is still sort of offering the HP 35670A 2 or 4 channel FFT Dynamic Signal Analyzer, DC-102.4 kHz but the price is way too high for what can be afforded for four lab stations. I have also looked at Bruel and Kjaer LAN-XI systems which are nice but also probably out of the budget for four of them.
Any other recommendations for dynamic signal analyzers for a reasonable price? Hopefully under ~$2500 each?
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I am looking for an inexpensive dynamic signal analyzer if such a thing exists for a graduate lab course on control implementation that I am planning. The lab takes control theory concepts and applies them in a hands on manner using DC motor motion control as the vehicle for exploring control theory. For many parts of the lab the students will need to measure transfer functions, determine the magnitude of signals, etc. When I took a similar course I believe we used HP 35665A 2-Channel DC to 102.4 kHz Dual Channel Dynamic Signal Analyzers which are now obsolete. Almost all spectrum analyzers I have found do not go to low enough frequencies. I need an operational frequency span which approaches DC on the low side, has multiple source modes such as random noise, periodic chirp etc, and can compute transfer functions, and display the coherence.
Keysight is still sort of offering the HP 35670A 2 or 4 channel FFT Dynamic Signal Analyzer, DC-102.4 kHz but the price is way too high for what can be afforded for four lab stations. I have also looked at Bruel and Kjaer LAN-XI systems which are nice but also probably out of the budget for four of them.
Any other recommendations for dynamic signal analyzers for a reasonable price? Hopefully under ~$2500 each?
Digilent Analog Discovery. The beta versions work on Linux and are scriptable.
Red Pitaya. ADC + FPGA (inc DACs/ADCs) + dual-core ARM, where you can program the FPGA and ARMs to do much more than just be a scope. See if there are any open source modules suitable for your purpose.
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As above or any of the low cost NI packages such as their myDAQ, do the students really need the measurement delivered in frequency domain?
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You can get one of these: MS3401A
10Hz to 30MHz frequency range, 0.01Hz frequency resolution, -20dBm to +20dBm input range, 100dB dynamic range; Measurements: magnitude, phase, delay time, magnitude / phase, magnitude / delay time.
These go for pennies on Ebay.
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The earlier version of the dynamic signal analyzer, the HP 3562A, would satisfy your requirements. I don't know what country you are in, but at least here in the USA, there are several of them presently on eBay in the $2,500 range. At that price, you get a warranty. Of course, if you really want to teach students some electronics, the "broken" ones often go for less than $500!
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For a stand-alone DSA, you might also consider Stanford: http://www.thinksrs.com/products/SR760770.htm (http://www.thinksrs.com/products/SR760770.htm)
These are in the US$5K range.
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The Analog Discovery board seems hard to beat for the price (myDAQ analog output is too poor to be useful though) but you'd have to add your own input protection. If they're working with motors students will find a way to blow it up otherwise.
There's also the Syscomp CircuitGear, but they don't mention the input voltage range so no idea about input protection.
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hp 3562A Obsolete yes, except the capabilities of this instrument remains classic, beautifully done with proper user ergonomics and measurement requirements properly considered and made in the rich hp tradition. For doing control system's work, it still shines in many ways. They can be repaired, full documentation is available and if the display tube is dying or dead, there are LCD conversions for them. This is from a 3562A owner's perspective. Until one has used one of these well, it's capabilities is not really appreciated. It just does so MUCH from FFT to Bode plots to S-plane displays to curve fitting and a lot more. It can be used for control system work to LF spectrum analysis, to filter work to modulation analysis and a LOT more. Most of all, it does all this as a stand-alone unit.
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1987-01.pdf (http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1987-01.pdf)
Good ones appear on ebay every so often for not a lot of $.
hp introduced the first replacement as 35665A, there after Agilent-Keysight offered a number of portable units. Stanford Research Systems also offers DSA's, never used them.
Bernice
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You can get one of these: MS3401A
10Hz to 30MHz frequency range, 0.01Hz frequency resolution, -20dBm to +20dBm input range, 100dB dynamic range; Measurements: magnitude, phase, delay time, magnitude / phase, magnitude / delay time.
These go for pennies on Ebay.
I need something that goes down to DC.
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I don't think you will want to wait that long for the transfer function to finish measuring.
The Circuitgear does 0.1 Hz to 10 MHz vector network analysis (the dynamic range is of course going to be inferior to a real DSA, but probably good enough ... and if they decide to use it as a load dump for a decent size motor you'll be out less money than with a real DSA). Get someone to create some labview programs for other functions you need, manpower is cheap at an university right :)
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They can be repaired, full documentation is available and if the display tube is dying or dead, there are LCD conversions for them.
Do you know if there are any LCD conversion kits for the 35665A? I looked around and could find some for the 3562A, and 3563A but not the 35665A.
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Newscope:
http://www.simmconnlabs.com/2001/index.html (http://www.simmconnlabs.com/2001/index.html)
Contact them to see if a kit is available. The 35665A uses a larger size display tube than the 3562A and related.
There are very good reasons why these kits are on the market.
IMO, for value and ... either the 35665A or earlier 3562A would be ideal for this work at the given budget.
Newer DSAs might have more features and ... functionality, they are not that different from the previous offerings.
Bernice
Do you know if there are any LCD conversion kits for the 35665A? I looked around and could find some for the 3562A, and 3563A but not the 35665A.
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Hi, I'm interested what you chose in the end? This does seem to be a tricky area.
Alan