Tuttnauer 2301006, Operation & Maintenance Manual

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Page 64 of 117 pages
5. CALIBRATION
The calibration of temperature and pressure is performed digitally.
The temperature and pressure measuring circuits, are designed with
components having a 1% precision. The temperature circuit is linear and has
an output of 100mV-2400mV for a temperature range 68
º
F-305
º
F.
The pressure circuit is also linear and has an output of 100mV-2400mV for a
pressure range 0-400kPa.
The measuring at the A/D is void for values higher than 2400mV or lower
than 100mV.
It is clear that even though the precision of the components of the circuit is
1%, the accumulated error can reach
±
5%, therefore calibration is
necessary.
The system is provided, with non-erasable memory in which the offset and
gain data of the sensors are stored.
This data may be input to the system, through programming or through the
autoclave.
In this chapter we shall describe the calibration of temperature and pressure
through the autoclave, the programming calibration procedure is altogether
identical.
Definition of Gain and Offset:
Every straight line can be defined by the equation ax+b=y. “a” is the deviation
from y=0 and “b” is the slope of the line. In our case a=Gain and b=Offset.
The system is based on calculation of offset and gain of two points as in the
following example. If the actual measured pressures are 100 kPa & 300 kPa
and the displayed pressures are 90 kPa & 310 kPa respectively, the ‘input Vs
pressure” graph will be as follows.
The calibration method enables to introduce these data into the system in
order to perform the automatic correction of the OFFSET and GAIN.
It is recommendable to find the two points which have to be input to the
system, before performing the calibration.
a
X
Y
INPUT FROM SENSOR
PRESUR
E
V
1
310
30
V
2
100
90
READ
ACTUAL