Barograph 'stiction'

Its Russell scientific in east dereham norfolk that is closing, so if you want any bits get in now.

Russel scientific close any time now, sad after so many years, mercury ban and electronics have done for them ! I have a modern Russel, a simple linkage but never seems to stick.. Noel.

Little vibrators were clamped on some aircraft instruments such as ASI's and alitmeters if the instrument panels did not have enough engine produced vibrations. With a slow moving instrument like a barograph, something timed to give a little tap every few minutes would be more suitable.

Thanks for the Russel Scientific information.

John

A tap every once in a while might well be the answer.

John

I thought it was worth following up this discussion with the present situation.

The simple bearings were cleaned and lightly oiled instead of trying to modify them looking for an improvement in reducing any stiction.

I have been plotting the readings against an on-line site over several weeks and I find that now the two graph curves are very similar. there is an off set due to a n ASL setup error but overall the barograph is working as expected.

So thanks for the advice and suggestions, all now seems to be well.

John

back in my uni days physiology recordings were made using a smoked drum - a messy process of running the recording paper through a smoky incomplete combustion source. Presumably the stylus friction was minimised. Recordings could be stored after spray varnish. Presumably a modern answer would be laser or point light source and photo responsive paper (or just a digital record). My ECG machine used a heated stylus and sensitive paper.

pgk

Going back to my Dome Barograph to further investigate the ‘stiction’ as I called it. I have found the cause to be the two sleeve bearings supporting the pen shaft. When air pressure changes direction the pen indicates the true reading for a small change but then lags behind. The sleeve bearings have some looseness so that at a change of rotation the pivoting is rather like a knife edge bearing for a degree or two. Then the pen shaft begins to climb up the side of the outer part of the sleeve so causing a lag in response to the pressure change.

I have replaced these sleeve bearings with miniature instrument ball bearings ensuring that the mechanical change can be reversed if necessary. The improvement in performance has been remarkable, going from a mere indication of the atmospheric pressure changes to something that truly follows the actual readings at my local airfield.

To say the least, the barograph has been transformed and this has happened following my digesting of the previous postings and a bit of lateral thinking. So many thanks to all who offered their suggestions.

John

Good to know that you have solved the stiction, the mod is superior to the original makers design.