LumaSense Technologies ISR 12-LO/GS - Handbuch (Seite 17)

IMPAC pyrometers ISR 12-LO/GS
17
In ratio mode (2-color mode) which is used for pouring stream measurements, the pyrometer is measuring
simultaneously with 2 sensors in adjacent wavelengths. It calculates the temperature by ratioing the radiation
intensities of the two wavelengths. This ratio technique eliminates a number of factors that degrade the accu-
racy of a conventional single color instrument e.g. measurement independent of emissivity in wide areas,
unaffected by dust in the field of view, unaffected by dirty viewing windows or lenses or if the measuring ob-
ject is smaller than the spot size of the pyrometer (at pouring stream measurements), etc. In some cases the
emissivities of the two wavelengths can differ so that it is necessary to correct the ratio of the two emissivities
(
ε
1 /
ε
2) to get a correct temperature reading. This correction can be done with the emissivity slope setting
K. The K-factors of metals or a pouring stream are normally higher than 1. For a correct measuring result it is
recommended to make a comparison test, e.g. with a thermocouple probe. Then the K-factor has to be cor-
rected until the pyrometer shows the same temperature value.
Emissivity values and emissivity slope values of various common materials are listed below:
Measuring object
Emissivity
ε
(at 0.9 µm)
Emissivity slope
K
„Black body furnace“ 1 1
Steel, molten 0.3 1.05
Steel heavily scaled 0.93 1
Steel rolling skin 0.88 1.00 ... 1.01
Slag 0.85 1
Chromium, bright 0.28 ... 0.32
Brass oxidized (tarnished) 0.65 ... 0.75
Bronze, bright 0.03
Copper, oxidized 0.88
Nickel 0.22
Gold, Silver, bright 0.02
Porcelain glazed 0.6 1
Porcelain rough 0.8 ... 0.9 1
Graphite 0.8 ... 0.92 1.01
Chamotte 0.45 ... 0.6 1
Earthenware, glazed 0.86 ... 0.9 1
Brick 0.85 ... 0.9 1
Soot 0.95 1
8.3
Exposure time (t
90
/ s)
The exposure time is the time interval when the measured temperature has to be pre-
sent after an abrupt change so that the output value of the pyrometer reaches a given
measurement value. The time taken is to reach 90% of the recorded temperature differ-
ence. In the “min” position, the device operates using the time constant 2 ms.
The dynamic exposure time adjustment prolongs the exposition time at the lower range
limit.
8.4
Clear time of the maximum value storage (tClear)
If the maximum value storage is switched on always the highest last temperature value
will be displayed and stored. The storage has to be cleared at regular intervals for ex-
changing by a new and actual value.
This feature is particularly useful when fluctuating object temperatures cause the display
or the analog outputs to change too rapidly, or the pyrometer is not constantly viewing
an object to be measured. In addition, it may also be beneficial to periodically delete
and reset the stored maximum values.
The following settings are possible:
OFF:
At clear time “OFF“ the max. value storage is switched off and only momentary values are
measured.
0.01...25 s: If any clear time between 0.01 s and 25 s is set, the maximum value is estimated and held in
double storage mode.
After the entered time the storage will be deleted.
extern: The external clearing can be activated and used within an own software (see section 13, Data
format UPP
® ) or via an external contact (for connection see 4.1 Pin assignment for the male
Settings:
min
0.01 s
0.05 s
. . .
9.99 s
Settings:
OFF
0.01 s
. . .
25 s
extern
auto
hold