82
PROCEDURES OPTIMISATION IN THE QUALITY SYSTEM
V
G. Bezoari, F. Guzzetti
Dipartimento I.I.A.R. - Sez. Rilevamento - Politecnico di Milano
Summary
The results of procedurea optimisation in the activity of “Gino Cassinis” Laboratory of Politécnico of Milan are
discribed in this report. The laboratory works into Politécnico of Milan’s Quality Sistem for the determination of
instrumental standard deviation of teodolites, diastimeters and levels.
1- Introduction
This Memorial Meeting organized with sensibility
by prof. Mussio in memory of Prof. Cunietti gives
us the possibility to make some considerations on
the activities that the Survey Department of DIIAR
(once "Istituto di Topografia, Fotogrammetria e
Geofisica" headed for many years by prof. Cunietti)
is carring on.
The activity related to the Quality System started
and had its impulse with prof. Cunietti who had a
deep knowledge of the topographic instruments.
We have to remember that prof. Cunietti
suggested to name our Quality System laboratory
after prof. Gino Cassinis (ISPRS President, Rector
of the TU of Milano and Major of the same city),
our distinguished predecessor at the Topography
Institute as principle of the chair later occupied by
prof. Cunietti.
After this right and opportune introduction, we want
to observe that one of the prerogatives of the
System is the constant check of the plannings as
well as the obtained results. That is to say that the
application of operative methods needs continuous
checks.
These checks that are made every half-year often
lead to the introduction of method variations.
These variations can be defined as optimisation
interventions.
We want to illustrate the modification about the
taratura of the teodolites until now carried out with
another procedure that was dated before July
1997, when the "Gino Cassinis" Quality System
Laboratory began its activities.
2 - Procedures
The measures and calculation procedures have
been studied so that the errors have no influence
on the search of precision.
Tests results are due to casual influences that are
difficult to analyse: the causes derive from all the
instrument parts, from the operator and are heavily
influenced by metereological and illumination
conditions.
W'e chose to work on the ground and our
suggestion is to work in normal, not in extreme
conditions.
Working in different conditions it is possible to
know metereologicai condition influences: This isn’t
a laboratory goal; so the reccomendation is to work
during normal (not extreme) condition.
Using the same procedures with a significant
number of instruments of the same model
(minimum 4) it is possible to define the
characteristics of that instrument model. Also this
isn’t a goal of laboratory activity. Besides if is
possible to make this evaluation using all the
reports result from our activity; in this case the
results dipend also from the rectified conditions of
instruments that arrive to the laboratory.
The DIN 18723 assumes the standard deviation to
represent the instrument precision. For this reason,
different series of Ij measures are earned out in
relation to the kind of instrument; every j serie is
characterized by a certain number of rij values
referred to the same largeness (considered
undipendent).
The simplest example is the settling of the
standard deviation of teodolites: once fixed the
instrument, we define 5 aims sc in a suitable place
and distance.
The measure operation can be repeated with the
strata method, in a quite short time and anyway in
the same conditions. Every statum str is made by
5 lectures that determine 4 angles. Since we don't
know before the angle that we are going to
measure, to create a ripetition it is necessary to
make at least two strata; the number of indipendent
measures rij that we see is:
rij = (,str - l) • (sc - l)
This number is made by a serie that has in itself
the characteristics of repetition but this is up to the
operator and the weather conditions. Mean square
errors analisys of the measured values compared
with mean value constitutes a dispersion index that
is characteristic of the whole instrument, operator
and ambience.
This formula defines the difference of the value:
where /j is the medium of I values of j serie.
Of course it results:
It is poss
time in o
same ins
different ’
operator
"accident;
Statistic
standard
the additi«
The serie
The f vali
operation
be obtaim
the indipe
number o
j
The stanc
made in 1
relation:
s
This vali
teorethica
number r
us deterrr
is contair
determine
correspor
in DIN 18
coefficien
o
Each pr
reference
forms acc
zenit, dist
3 - Optim
The aim
the stani
function <
redundan
consi d ere
increases
measures
significati
number o
From one
measures
below); c
number c
cost) for c
We decid
values ar
