EW Barograph & Logger Models A, B and C - Notes



This page supplies some miscellaneous information on the EW Barographs and Loggers models A, B and C. These are the English language gliding loggers with keyboards and LCD displays. It does not apply to the French model F, though many details of that are the same. It also does not apply at all to the model D or to any of the non-gliding loggers.

This information is supplementary to data supplied by EW Avionics and does not form a specification. It is provided for guidance only and the performance of actual hardware and software which has already been supplied or which may be supplied in the future may be different. The user of this information takes all responsibility for its application.

The terms "barograph" and "logger" are used pretty interchangably. All of the units are really both but "barograph" can also be taken to mean a logger which only records pressure altitude, not GPS position information, and "logger" can be taken to mean a barograph which also records GPS information.

Version History

This section lists some details of various versions of these loggers for which information is available to hand at the time of writing. I made this list while researching the event texts described below and it seemed a pity to loose it.

Version numbers consist of the last two digits of the year followed by a two digit week in year number (ISO 8601 week numbering). This is followed by the model letter: 'A' for 10km height range, 'B' for 12km and 'C' for 15km. Only a very few 'C's were produced, mainly for balloon related record attempts.

90ww: an internal development version - the earliest source code easily available. The earliest barographs were produced in the 1980s.

9210: released version.

9305: earliest released version with GPS recording. Included GPS connect, disconnect and fix missed events and fixes of logger clock time against UTC time of day.

9425: fixed a problem with 9305 which did not validate the digits received from the GPS for the UTC time. If corruption happened on the serial connection a syntactically invalid trace which would not upload could be produced. Also added the French version.

9437: further changes not relevant to events.

9439: futher changes not relevant to events.

9503: first version which recorded the geodetic datum supplied by the GPS. Also, stored the UTC date if that was available in fixes of the logger's clock against UTC as reported by the GPS. Dropped the fix missed event (because it resulted in full logger memory if there was an intermittent connection to the GPS). Added XModem upload of the trace but this has never been used.

Unfortunately, two of the key versions regarding GPS support are confusingly 9305 and 9503.

9539: removed the camera related inputs and replaced them with the fast sampling facility.

9540: added "long flight mode" were a lot of GPS information is not stored when the sample interval is long in order to stretch the memory as far as possible. This was for trans-Pacific or round-the-world balloon flights.

9551: added "NMEA guard time" - a short delay before using data from a newly connected GPS to work around bad data from some Garmin models as they are switched on. Also, the way the datum is stored was changed so that the last two non-blank characters were always kept.

9616: added the security code required for IGC approval.

9815: fix to problem with reading the real-time-clock chip which resulted in occassional Error 1 messages. Also added some debugging facilities related to this including the possibility of a message starting "Trace incident flags " in the numeric trace header.

9817: fix related to datum recording when the GPS restarts fixing.

9830: special version with a default sample interval of 180 seconds based on version 9815 (not 9817). For a round-the-world balloon flight, I think.

9846: based on version 9817, reads the real-time clock twice at each attempt and reports an error if the value had changed in between. I think this was added because of problems found with the clock hold function found during the development of the model 'D' which might have been additional reasons for the Error 1 events other than the one fixed in version 9817.


This section describes the format of event lines and event-like lines in the numeric trace print. It also applies, partly, to the equivalent lines in the graphic trace print.

By "event-like" lines we mean ones for fast samples, UTC fixes and datum records which are not actually stored as events in the logger's memory but which could be treated as events by upload software. (EWView/DOS and EW Windows Uploader treats some of these as events and some specially).

With literal text in double quotes, spaces represented by OPEN BOX ("") and non-terminals to be substituted for in angle brackets, the general syntax of an event line is:

<HH>":"<MM>":"<SS> "" <event-text> ",␣altitude␣" <press-alt> [ "" <gps-alt> ]? [ "" <position> ]?

This syntax applies to all of the "proper" events and also to fast samples, except that fast samples don't have the text ",␣altitude␣" between the event-text and the pressure altitude - they just have a space. This syntax does not apply to UTC fixes or datum records.

<HH>":"<MM>":"<SS> is the time of day of the event determined by the logger's clock.

<event-text> is text describing the event. In all cases it is just a fixed string except that in the case of tag events it also includes the tag number entered by the user.

Event text Start version End version Description
Tag␣number␣<tag-num> - - Tag button on logger keyboard pressed.
Contact␣close - - Logger contact closure input (pin 6) connected to ground (pin 5).
Contact␣open - - Logger contact closure input (pin 6) disconnected from ground (pin 5).
Photo - 9503 Photograph taken by camera attached to logger.
Camera␣connect - 9503 Camera connected to logger (pin 9).
Camera␣disconnect - 9503 Camera disconnected from logger.
GPS␣connect 9305 - Started receiving characters from a GPS receiver.
GPS␣disconnect 9305 - Timeout receiving characters from a GPS receiver.
GPS␣fix␣missed 9305 9439 Timeout waiting for a position from a GPS receiver.
Fast␣sampling 9539 - Event input pin (9) taken to ground.
Fast 9539 - Extra data point recorded during a period after the event pin has been taken low.
Clock␣reset 9539 - Code related to this event is present in version 9539 and later but I do not think any released versions could actually generate it. EW Windows Uploader parses this string but ignores the event on export to .IGC files.

Start version is the earliest known version of the logger to produce this event. "-" if present in pre-1990 loggers. End version is the latest known version of the logger to produce this event. "-" if present in last A, B or C loggers produced.

tag-num is a number entered by the user on the logger's keyboard. It is in the range 0..9999 and is represented using 1 to 4 decimal digits.

press-alt is the pressure altitude at the time of the event. It is in metres relative to the 1013.25 pressure level and is in one of the following formats, the one which gives the fewest leading zeros:


gps-alt is the altitude as reported by the GPS. It is in the same syntax as the pressure altitude except that the decimal point is replaced by the upper case letter 'G'. It is only present in versions 9503 and later when the information is available from a connected GPS.

position is the latitude/longitude at the time of the event. It is only present in version 9305 and later when the information is available from a connected GPS. Yes, that's right: positions were introduced in version 9305 but GPS altitudes came later, in version 9503.

UTC fixes record the logger's clock and the corresponding UTC time reported by the GPS receiver. These fixes can later be used to correct the logger clock times to UTC. UTC fixes were introduced in version 9305 and extended to include the UTC date (in addition to the UTC time) in version 9503. UTC fixes are recorded every half hour when the GPS is fixing.

The syntax of a UTC fix line is:

<HH>":"<MM>":"<SS> "␣UTC␣" <HH>":"<MM>":"<SS> [ "␣"<YY>"-"<MM>"-"<DD> ]?

The first HH:MM:SS is the logger clock time of the fix. The second HH:MM:SS is the UTC time of day of the fix. The YY-MM-DD is the UTC date of the fix. It is only present in version 9503 and later and is only present if the date is available from the GPS receiver.

In version 9305 the digits in the UTC time received from the logger were not validated. Therefore, in the case of corruption on the serial line it was possible that characters other than digits were stored causing a trace to fail on upload (this happened once to my knowledge). In version 9425 the characters received from the GPS are validated.

Datum records are recorded in the trace when the logger first sees a datum sentence from the GPS receiver and whenever it subsequently sees a datum sentence with a different datum. They are only present in logger versions 9503 and later.

If datum sentences are found to be missing after one or more datum records have been recorded then a datum record with a datum of "*********" (nine asterisks) is recorded.

The syntax of a datum record is:

<HH>":"<MM>":"<SS> "␣Datum␣" <datum>

The datum text is always nine characters long. If the datum in the NMEA sentence from the logger is shorter than this it is blank padded.

In logger versions before 9551, datum names longer than 9 characters are simply truncated. In version 9551 and later, once 9 characters have been received any subsequent non-blank characters overwrite the last two characters in the buffer. The effect is to store the first 7 characters and the last two non-blank characters. The idea is to disambiguate long names which are different only in the two digit year number traditionally added to the end of datum names.