- -
28
THE
PROBES
The probes of the graphic datalogger are equipped with an "intelligent" module which acts as an in-
terface between the sensor in the probe and the multifunction instrument. Inside this module there is
a microprocessor circuit with a permanent memory which performs various function:
•
it enables the datalogger to recognise the type of probe connected: Pt25, Pt100, Pt500, thermo-
couple, humidity probe, pressure probe, anemometric probe;
•
it memorises the probe calibration data: in this way it can be used on any one of the instrument’s
three inputs, or on a second instrument, without having to be recalibrated;
•
it recognises the instrument with which it was calibrated (user calibration);
•
it maintains the factory calibration data and those of the last calibration done by the user, which
may be protected by a password. If enabled, the user can choose which calibration to use for
each of the probes connected to the instrument;
•
it memorises a serial number which allows the unmistakable identification of the probe. This is
useful if several probes of the same type are being used at the same time.
The recognition of the probes takes place when the instrument is switched, after reset (function
“
6) Reset”
of the Menu) and during calibration, when proceeding with calibration of the probes
connected to the inputs (
see the general section on calibration on p.23 and the individual models in
the next chapter
).
The instrument memorises which probes are connected to its inputs: if on switching on it finds that
there has been a variation, for example because a probe has been disconnected, it notifies the opera-
tor with the message: “WARNING!
CHANGE OF PROBES DETECTED –Press NOW any key to
choose settings or wait to self-config
”. When any key is pressed within 3 seconds, a menu is
opened in which the instrument configuration parameters may be modified. If you do not consider it
necessary to modify them, it is sufficient to wait 3 seconds to return to the standard measuring con-
ditions. If you disconnect a module, the notice
“COM FAILURE”
(communication error) will ap-
pear, indicating that there is no communication between the module and the instrument: insert the
probe again in the same input to restore correct measurement conditions.
For further details on the probe, see the paragraphs below concerning the individual measurements.
Pt100
TEMPERATURE PROBES
The DO9847 accepts at input Platinum temperature probes with a resistance from 25
Ω
to 500
Ω
.
Platinum probes have 4-wire connections, the energising current is chosen in such a way as to
minimize the effects of self-heating of the sensor.
All Pt100 probes are calibrated in the factory: the user can choose whether to use this calibration or
to make a new one and even protect it with a password (
see the heading “1-3) Probe options” on
p.16
).
The user can choose what unit of measurement to use for viewing and printing from among those
allowed with Pt100 probes °C, °F or °K (see the instructions for selecting the unit of measurement
on p.10).
In the appendix of the instructions manual there is a description of the mathematical function used
by the instrument for finding the temperature as a function of the sensor resistance and the meaning
of the coefficients R
0
,
α
,
δ
and
β
:
see p.116
.
