FW: Tesa Tape / Loggers

[j...@oxaero.com]

Tony, Rob,

 

Here is a sample altitude data from the your recorder.  This is altitude graph in Cambridge Aero Explorer.  I had to replace the header records with Cambridge records to make CAE take the file.  Like Wolley’s, this logger is not up to snuff either.  Blue is GPS and Red is pressure altitude.  There is too little resolution, so that only large altitude changes change a value.  I do not know whether this is a limitation in the EW logger as regards the GPS altitudes or not.  Since the pressure altitudes that I presume come from a pressure sensor in the logger have the same problem, the limitation could be in the logger so a better GPS would not give you higher GPS data.

 

 

For comparison, below is a sample of data from a good logger, Wolley’s LX5000.  My CAI 302 is the same.

 

 

I recommend investing is a better logger before trying to take data.

 

Sorry,

Jim

 

From: Tony Lintott [mailto:derby...@yahoo.co.uk]
Sent: Friday, November 18, 2011 12:06 PM
To: j...@oxaero.com
Subject: Re: Tesa Tape / Loggers

 

Hi Jim,

 

Will sign up to G Groups but 'the system' won't let me at present.  I keep getting this message but I'll keep trying over the weekend.

 

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• Have received your invoice for tape which I'll pay pronto.
• Regarding Adam's poor logger, I've attached an igc file from my logger.  Perhaps you'd oblige by telling me whether I should change the logging frequency.
• For altitude I use a Garmin 12XL GPS.

Rgds, Tony

 

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From: "j...@oxaero.com" <j...@oxaero.com>
To: Tony Lintott <derby...@yahoo.co.uk>
Cc: Deturbulator Participants <deturbulator...@googlegroups.com>
Sent: Friday, 18 November 2011, 13:23
Subject: Tesa Tape / Loggers

Tony,

 

Ok.

 

BTW, I got the first log from Adam Woolley, in AU.  His logger seems to be a really poor one.  The GPS altitude data is very unreliable and does not track the pressure altitude closely at all.  Also, the pressure altitude data is stair stepped because it records at a very low resolution, changing only about every 12 seconds.

 

Check some of your old logs to assess the quality of your logger before spending the money for a high tow.

 

I think that Adam can use his logger if he holds his speeds for say 2-3 minutes.  That means that he will have to narrow the range of speeds he tests in order to make the best use of his altitude.  Another logger is the best idea.

 

BTW2: If you haven't already done so, please join the Deturbulator Participants Google Group.  The list of people I have to remember to cc is getting long.  Thanks.

 

Jim

On Nov 18, 2011, at 2:18 AM, Tony Lintott <derby...@yahoo.co.uk> wrote:

Hi Jim,

 

Please send me a bill for the second lot of tape in transit. 

 

The first lot has arrived.   No tracking, no announcement, just appeared in the mailbox!

 

Rgds, Tony

 

[j...@oxaero.com]

Tony,

First, install Cambridge Aero Explorer on your PC.  It has the best altitude plot for examining the individual altitude samples in an IGC file.  But, it only wants to open files created with a Cambridge logger, do it is necessary to replace all the header records (all before the first "B" record) with header records from a Cambridge log to fool it.

When it opens a log, it shows the altitude traces at the top and the ground track at the bottom.  Drag the border between these down to the bottom to stretch the altitude display vertically.

Right click on it, select ZOOM and drag across a section of the display to select the samples to stretch horizontally.

 You will see the individual altitude samples as in the two images that I sent you.

If you get smooth curves as in the LX5000 log, then the logger is ok.  But if it regularly holds the same altitude number for more than 4 seconds, resulting in a stair stepped trace, then it lacks the resolution needed.

Increasing the sample rate to 1 Hz will not help, you will only fill in the steps with more samples at the same value.  It's a problem of the number of bits in a data word.  Cheap equipment with little memory use 8 bits (412 values).  Better devices use 12 or 16 bits (64,128 values), hugely better resolution.

In CAE, pressure altitude displays in red and GPS in blue. You can click on a sample point and the window header will display both numerical values along with the time.  The right and left arrow keys can be used to mine to the next sample right or left.  This lets you check the sample timing.  If the logger drops samples, because it cannot keep up, you will se the gap visually and can verify it in the window header.

Some mobile glider software has logging capabilities.  Since they may receive only GPS data, they duplicate that in the pressure altitude field of the "B" records.  Conventional wisdom says that GPS altitude data is unreliable.  That is not necessarily true.  It does have less accuracy than lat/long data, but it is not necessarily unusable for our purposes.  For us, DC offset errors do not matter since we use the slope of data, not the absolute value.  It only needs to follow altitude changes with sufficient resolution and with consistent accuracy.  

I can supply the CAE install file and a Cambridge header if you need them.

You will need a simple ASCII text editor to paste the Cambridge header over foreign header.

I hope thus helps.

Jim

On Nov 30, 2011, at 5:12 PM, Tony Lintott <derby...@yahoo.co.uk> wrote:

Jim,

If you give me guidance on how to do a logger check I'll ask for files from club members and check 'em out. I'll also establish their logger make/model this way. The other thing I should mention is that I can increase the data logging rate of my EW down to 1 second intervals.  Think I'm on 5 at present.  Will this help?

Rgds, Tony

---

From: "j...@oxaero.com" <j...@oxaero.com>
To: 'Tony Lintott' <derby...@yahoo.co.uk>

Sent: Wednesday, 30 November 2011, 22:59
Subject: RE: Tesa Tape / Loggers

Tony,

 

No need to get an LX5000.  Check the logs of some of your friends with cheaper loggers and see how good they are. 

 

This would be a good thing to put on the SC Group.  Asking what loggers people use that cost within your price range.  Then ask specific responders for sample logs.  It may be possible to harvest logs from OLC if OLS specifies the type of logger that was used.  It’s beginning to look like I need to survey the field and make a list.

 

Jim

 

From: Tony Lintott [mailto:derby...@yahoo.co.uk]
Sent: Wednesday, November 30, 2011 3:54 PM
To: j...@oxaero.com; Roy Hendrix; jari.hy...@linflow.se
Cc: 'Rob Barsby'
Subject: Re: Tesa Tape / Loggers

 

Hi Jim,  Thanks for the 'bad news'.

 

The cost involved with LX5000 etc. systems is prohibitive so we're going to have to find another way.  Not being very technical I'm struggling at present but perhaps the group knowledge could come to my aid.  Perhaps you could forward to other participants as your embedded address for the group 'bounced'.  So ......

 

This is the spec of my current logger where I read that the altitude resolution is 5m steps up to 10000m

 

                                                   Case:  Powder coated aluminium extrusion        

                                       Dimensions:  57 mm x 32 mm x 170 mm

                                               Weight:  ~290 grams including internal battery

                                             Memory:  128 Kb Static RAM

                                               Battery:  PP3 9v or equivalent alkaline or lithium

                                       Battery Life:  Up to 50 hours, dependent on temperature

                                 External Power:  9v to 16v DC

                         Power Consumption:  recording<15 mA . Standby ~25µA  

                                  Internal Clock:  Date/time crystal controlled

      Operating Temperature Range: -10° to +40° C

                                Sample Interval:  1 to 999 seconds (in non-volatile memory)

                                  Altitude Range:  -350m - 15,000m referenced to 1013.2 mb

                          Altitude Resolution:  -350m - 10,000m: 5 metre steps

                                                               10,000m - 15,000m: 10 metre steps

                          Recording Capacity: ~12 hrs per second sample interval (altitude  only),  ~6 hrs per second of sample interval (altitude & NMEA)

                                          Connector:  9-pin D (non-standard connections)

                          Connection to GPS:  NMEA 0183 Version 1.5 or 2

          Other External Connections:  Pilot event button, motor contact, external power input

             Communications Standard:  NMEA:    Serial 4800 baud

                                               PC:      Serial 9600 or 19200 baud

 

Having reviewed the LX5000 manual I can find no equivalent data, likewise for the CAI 302, so I can't compare.  Can anyone assist?

 

Rgds, TonyL

 

 

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From: "j...@oxaero.com" <j...@oxaero.com>
To: 'Tony Lintott' <derby...@yahoo.co.uk>
Cc: 'Rob Barsby' <r...@shinx.co.uk>; deturbulator...@googlegroups.com; Roy Hendrix <rwhe...@mac.com>; jari.hy...@linflow.se
Sent: Tuesday, 29 November 2011, 20:07
Subject: FW: Tesa Tape / Loggers

Tony, Rob,

 

Here is a sample altitude data from the your recorder.  This is altitude graph in Cambridge Aero Explorer.  I had to replace the header records with Cambridge records to make CAE take the file.  Like Wolley’s, this logger is not up to snuff either.  Blue is GPS and Red is pressure altitude.  There is too little resolution, so that only large altitude changes change a value.  I do not know whether this is a limitation in the EW logger as regards the GPS altitudes or not.  Since the pressure altitudes that I presume come from a pressure sensor in the logger have the same problem, the limitation could be in the logger so a better GPS would not give you higher GPS data.

 

<image001.jpg>

 

For comparison, below is a sample of data from a good logger, Wolley’s LX5000.  My CAI 302 is the same.

 

<image002.png>