Experimental Physics and Industrial Control System
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I agree.
I'm not even sure when one would use the backward conversion. Isn't it
always used forwards?
Pete.
Rolf Keitel wrote:
Andrew,
I am not sure if I understand your message correctly. Rejecting negative
slopes (in the second column) of the breakpoint table would be too
limiting. One can always arrange the raw value sequence in ascending
order. The engineering sequence slope is then determined by your sensor
(in our case Si cryo-diodes).
IMHO one doesn't have to go overboard with reengineering, as breakpoint
tables are not really used "on the fly".
Documenting the requirements of monotonous curves in both columns, a
positive slope in the raw column and fixing the code for the backward
conversion would be sufficient for me.
Of course, dynamically reloading of breakpoint tables at run-time would
be nice.
- rolf -
Andrew Johnson wrote:
D. Peter Siddons wrote:
I had also just run into this. It is also a bug in the makeBpt
program to generate a table from raw data. It produces nonsense if
the raw ADC values are in decreasing order and the engineering values
are increasing. I didn't try it with positive slope but reversed data
order. I thought that simply reversing the table order fixed it, but
apparently not.
Rolf Keitel wrote:
There is a problem with break-point table conversion from
engineering to raw values ( function cvtEngToRawBpt in file cvtBpt.c).
The function returns incorrect results, if the breakpoint table has
negative slopes, i.e. if engineering values decrease with
increasing raw values.
I couldn't find anything in the documentation when I looked briefly
the other day, but I don't think the present breakpoint table code was
ever supposed to work with negative slopes. Given the limitations of
the existing code though it really ought to check its inputs properly
and refuse to load a breakpoint table that slopes downwards.
Any replacement code that permits negative slopes should reject curves
that are not continuously increasing or decreasing but have local
minima or maxima - I have no idea what the existing code does with
such curves, but I doubt that it's pretty. We would also like to be
able to reload breakpoint tables at runtime (which I believe Benjamin
Fransken implemented for BESSY but this isn't available in the
official release).
Any offers to do a proper re-engineering of this (fairly
self-contained) area of functionality in EPICS Base? If no-one offers
I'll try to put in the positive slope test, but if a site needs more
than that it'll have to donate some effort towards implementing it.
- Andrew
- Replies:
- Re: bug in break-point table conversion Rolf Keitel
- Re: bug in break-point table conversion Andrew Johnson
- References:
- bug in break-point table conversion Rolf Keitel
- Re: bug in break-point table conversion D. Peter Siddons
- Re: bug in break-point table conversion Andrew Johnson
- Re: bug in break-point table conversion Rolf Keitel
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ANJ, 02 Sep 2010 |
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