[SS2S-Main] Re: temperature measurement

  • From: Ken Biba <ken@xxxxxxxxxxxxxx>
  • To: "sugarshot@xxxxxxxxxxxxx" <sugarshot@xxxxxxxxxxxxx>
  • Date: Tue, 25 Mar 2014 16:05:50 -0700


Should do great for recovery location ... it is the trajectory location that 
separates the GPS chipsets IMO.

Our flights are to 70-180k' MSL ... tickling Mach 3 ... so we are testing the 
limits of modern comercial GPS chipsets.   So far the best has been uBlox.   
Altus Metrum used to use the MediaTek, but recently switched to uBlox.

But this chipset does have "similar" specs - 515 m/s velocity, 40 km altitude 
... I would be curious about the dynamics.

I would have to dig out my old spreadsheets .. but there is such an obvious 
difference between a chipset that is prepared to deal with dynamics and one 
that is not.   Most of my testing ahs been with SiRF, uBlox and Trimble 
chipsets.   Getting lock is not sufficient .. .what is interesting is that 
reported location, under lock, is dramatically false for SiRF ... while largely 
accurate for uBlox and Trimble (when set to high dynamic mode) up to modest 
accelerations (<6-8 g).


Ken Biba

> On Mar 25, 2014, at 3:54 PM, "Nev Blyth" <nev.blyth@xxxxxxxxx> wrote:
> Hi Ken
> (Apologies for getting OT here).
> I've only flown the MTK3339 based module three times - on H & I motors. 
> During those flights (3K ft only) I was not directly logging the NMEA stream 
> on board - rather I was using a simple telemetry system to stream the NMEA to 
> a recording ground station. Those flights showed valid data throughout, but 
> admittedly, the dynamics were rather benign in the scheme of things.  I'll 
> have a look at the altimeter log for velocities.
> The axis of the GPS patch antenna was aligned normal to the vehicle's axis. 
> Admittedly, my main motivation was recovery location, not trajectory 
> recording, but I'll take what I get!
> Nev B
> —
> Nev Blyth
> 0407 923 182
>> On Wed, Mar 26, 2014 at 8:20 AM, Ken Biba <ken@xxxxxxxxxxxxxx> wrote:
>> Nev:
>> Now I'm curious.   I fly the uBlox in large part because its signal 
>> processing seems to do really well for high dynamic flight (and while it has 
>> a spec limit of 50km, the factory says it will report above that altitude, 
>> though with diminished precision).   It does stop reporting above the spec 
>> limit of ~515m/s ... though does resume reporting when the speed drops below 
>> that.
>> Many GPS chipsets perform poorly in high dynamic rocket flight ... since the 
>> signal processing is biased to solve the 2D problem with high precision 
>> rather than the fast changing 3D problem.   The uBlox has a specific 
>> configuration parameter to set the movement model ... I don't see that on 
>> the MediaTek manual.
>> Do you configure in default mode?
>> Ken
>>> On Mar 25, 2014, at 2:08 PM, Nev Blyth <nev.blyth@xxxxxxxxx> wrote:
>>> Nathan - the adafruit GPS module is excellent - has flown multiple times in 
>>> my high-power rockets and maintained a solid lock throughout the whole 
>>> flight. If I recall, the module is programmable, has PPS output and the 
>>> price is excellent.  Would be interesting to compare against the ublox 
>>> offerings.  The external antenna connection is a bonus for me.
>>> Cheers,
>>> Nev. B
>>> ___________________
>>> Nev. Blyth, VK1HNB
>>> Canberra, ACT, Australia
>>> @nevblyth
>>> facebook.com/nevblyth
>>>> On 26 March 2014 05:40, Nathan Asdourian <rawliquid@xxxxxxxxx> wrote:
>>>> you would be much better off with a ublox that is fully configurable and 
>>>> reprogrammable,  not to mention the latest version has a compass module in 
>>>> it.... i think it's more than $40 though it is the unit from 
>>>> 3drobotics.com and what i use in my helis
>>>>> On Mar 25, 2014 10:47 AM, "Rick Maschek" <rickmaschek@xxxxxxxxxxxxxx> 
>>>>> wrote:
>>>>> Hi Nathan,
>>>>> and this may be going up on our next Near Space balloon launch: 
>>>>> http://www.adafruit.com/products/746 
>>>>> Are bitcoins worth anything anymore?
>>>>> Rick
>>>>> On Tuesday, March 25, 2014 6:37 AM, Nathan Asdourian 
>>>>> <rawliquid@xxxxxxxxx> wrote:
>>>>> Please forgive me if these items are irrelevant due to the extremes 
>>>>> needing to be dealt with but I just saw a new board get released here a 
>>>>> few weeks ago,  and all the related things seem to be under $20
>>>>> http://www.adafruit.com/index.php?main_page=adasearch&q=thermocouple
>>>>> And of course if anyone has some bitcoin stashed away,  they will accept 
>>>>> that for payment...
>>>>> On Mar 24, 2014 9:20 PM, "Lampe, Mattias SLC CT PEK" 
>>>>> <mattias.lampe@xxxxxxxxxxx> wrote:
>>>>> Hi Richard,
>>>>> my personal choice would probably be to use an integrated chip that does 
>>>>> everything, including D/A-conversion, e.g. the MAX6675:
>>>>> http://item.taobao.com/item.htm?spm=a230r.1.14.48.TLryFm&id=13831142184
>>>>> Since it may be more convenient for you to use the existing DAC, you may 
>>>>> prefer one of the older chips with analog output, though. AD595 would be 
>>>>> a good choice:
>>>>> https://www.sparkfun.com/products/306
>>>>> Of course you'll need to have a loot at the datasheets to see whether the 
>>>>> devices match the temperature range you need.
>>>>> Hope it helps.
>>>>> Have a good day!
>>>>> Mattias
>>>>> >-----Original Message-----
>>>>> >From: sugarshot-bounce@xxxxxxxxxxxxx [mailto:sugarshot-
>>>>> >bounce@xxxxxxxxxxxxx] On Behalf Of Richard Nakka
>>>>> >Sent: Monday, March 24, 2014 10:33 PM
>>>>> >To: sugarshot@xxxxxxxxxxxxx
>>>>> >Subject: [SS2S-Main] temperature measurement
>>>>> >
>>>>> >For an upcoming motor test, we would like to use thermocouples
>>>>> >(k-type?) to measure motor casing and nozzle temperatures.
>>>>> >We would like to use an 8-channel DATAQ unit for the data acquisition.
>>>>> >
>>>>> >We understand there are challenges to this due to small voltage
>>>>> >signal, non-linear temperature-voltage relationship and the need (?)
>>>>> >for a reference junction compensation.
>>>>> >
>>>>> >Question to list members: Can anyone give advice on how to do this?
>>>>> >What kind of amp would we need? Could anyone be of assistance in
>>>>> >designing/building such?
>>>>> >
>>>>> >
>>>>> >thanks in advance
>>>>> >Richard

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