Re: REQ: major electronics analysis project help needed TIA
- From: John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 04 Jun 2005 08:55:50 -0700
On Sat, 04 Jun 2005 08:01:09 -0500, JB2 <none@xxxxxxxx> wrote:
>On Sat, 04 Jun 2005 05:33:19 GMT, in alt.engineering.electrical you
>wrote:
>
>>JB2 <none@xxxxxxxx> wrote:
>>>I have to log 150 discrete inputs, some AC and others DC, voltages and
>>>currents. I plan on using simple inductive pickups and voltage probe
>>>points.
>>
>>How often do you need to log each input?
>Still to be determined, but preliminary data acquisition will need to
>be during major changes in flight profiles, such that sample rates may
>only be required when user selects the need and not a continuous
>sampling.
>
>> Do some inputs need to be logged more often than others?
>No, in fact would rather have all samples at the same time for
>comparative analysis.
>
>>What kind of voltage and current ranges do you need?
>Gen output is 40kVA three total & One 1kVA
>115v 1 phase 400Hz 650 amps
>115v 3phase 400 Hz
>220v 2Phase 400Hz
>28 vDC 200 amps max. There are two TRs tied together in parallel, EA
>max 100 amps. Loss of various equipment will be executed and data
>sampled for future capabilities and emergency procedures. The main
>concern is the capability of the TRs to handle various loading
>configurations but data for all sources is required.
>
>> Do you need analog measurements for everything, or is
>>digital OK for some of the inputs?
>Data will be used for reporting purposes, future calculations and
>modeling. I will probably end up building a more accurate model then
>currently exists (current model is solely analytical, no hard data
>available) All the sources are analog, but how those samples are
>obtained, I don't think will make a difference. I thought simple
>inductive pickups that feed analog to dig conv for recording.
>
>
>>How accurate does each analog reading need to be?
>Big question! I would want at most _+2%. I suspect any more
>deviation may make modeling too inaccurate.
>
>>
>>>Any suggestions?
>>
>>The 150 channel requirement is a biggie. If you don't need to log each
>>input that often, it's not as big of a deal, but if you need high data
>>rates, it may get a little expensive.
>>
>>>I know I'll need a DAC, just not sure which would work best.
>>
>>Budget?
>LOL yea right. in house resources avalablity of equipment., Next
>week I can check whats avalable, for now, I'm simply attempting to get
>a solid foundation for a POA.
>
>> If you have plenty of somebody else's money, and you don't need
>>to log each channel more than once every several seconds, go buy a data
>>logger like a Fluke Hydra. This is essentially a good auto-ranging
>>multimeter with a DP21T switch on the input leads. Some models can only
>>output the data immediately over a serial port, while some can store data
>>in an internal memory. The potential problem here is that it costs
>>US$2,000-$3,000 for 20 channels, and you need to do that seven and a
>>half times. You might be able to buy one data logger and multiplex the
>>inputs to it with external silicon, switches, or relays. You need a
>>40P8T contact arrangement...
>Outstanding suggestion
>>
>>Instead of trying to log everything at once on a laptop, it might work
>>better to select smaller boards with 10 or 20 inputs and let each board
>>log to local memory, then download all the boards at the end of the
>>flight. This may also tend to reduce the number of wires strung around
>>the aircraft, if you can locate the boards near the measurement points.
>>You need some kind of sync between the boards... they all have to start
>>their clocks at the same time, or get individually synchronized to GPS
>>or WWV, or you need to string a wire between them. You may also have to
>>be careful where you put the boards physically... if they make the
>>aircraft radios go screwy the pilot will not be happy with you.
>I do have GPS signals available
>>
>>This may be obvious, but it's probably a bad idea for there to be just
>>one person trying to fly the plane and operate the data logging at the
>>same time. If one-man operation is required, the interface to the data
>>logging has to be very simple, or even something that can be started
>>before takeoff by someone else and stopped after landing.
>I have a crew on board, flight crew, trechnicians, engineers (me) 707
>A/C
>
>
>>I'm somewhat curious as to what you're doing... most of the people that
>>want to do something like this probably work for an aircraft
>>manufacturer and in that case I would think they'd just buy
>>off-the-shelf stuff. But hey, maybe you're building an experimental
>>jet in your garage. :)
>I wish LOL no.... DOD trying to avoid using $$$$$ contractors, We
>have the resources, but money is limited and this is my 1st project of
>this magnitude that I'm heading up.
>
>>
>>Once you can answer most of the questions above - in other words, when
>>you can state your requirements more clearly - you may want to
>>cross-post or post to sci.electronics.design for more good input.
>>
>>Matt Roberds
>thanks Matt
My customers (biggish aerospace folks) tend to use VME systems for
this sort of thing. Your choices are
1. Log the raw data (waveforms) with ADC boards. This is simple but
would produce huge heaps of data that would have to be reduced into
things like RMS voltages, currents, RPMs, etc. This may require signal
conditioning ahead of the ADC channels. At high channel counts,
acquiring raw data can run out of system bandwidth.
2. Use signal conditioner boards that measure RPM, voltage, current,
power, whatever, and log their output. More expensive per channel, but
much less data and data reduction, and little or no outboard signal
conditioning.
Both require an infrastructure (VME crate, controller or embedded CPU)
and acquisition boards. Figure $4k or so for the baseline stuff, plus
$100-$500 per channel, roughly, depending on how you do it.
My company makes VME boards that acquire AC power, RPMs, load cells,
thermocouples, stuff like that. In something like jet engine testing,
it's common for hundreds of channels to be acquired at hit rates down
to a few milliseconds. See VITA.COM for most of what's available in
VME.
John
.
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