INFRATHERM
pyrometers IS 5 · IS 5-LO · IGA 5 · IGA 5-LO
44
8.3
Analog output 0...20
⇔
4...20 mA (DIP switch nr. 3)
When the switch is in the ON position, the analog output will be 0 ... 20 mA; in the Off
position, the analog output will be 4 ... 20 mA. The analog output has to be selected
according to the signal input of the connected instrument (controller, PLC, etc.).
Note:
If the settings directly at the pyrometer should be used the py-
rometer must be switched into offline mode
Note:
At 70°C, a thermal switch is activated at the 4 ... 20 mA output which sets the output
to 0 mA (simulates a “sensor break”).
8.4
Exposure time t
90
(DIP switches nr. 1 + 2)
The exposure time
t
90
is the time interval for the output of the pyrometer to go from the lowest value in the
pyrometer's measuring range up to 90% of the highest value in its measuring range, when measuring an
abrupt increase in temperature. (2 x t
90
= 99%; 3 x t
90
= 99.9% etc.). Independently of this, the pyrometer
performs a measurement every 1 ms and updates the analog output. Longer exposure times can be used to
achieve constant temperature reading if measuring objects have rapidly fluctuating temperatures. The DIP
switches can be used to set the exposure time. Select the respective jumper position:
DIP - 1
DIP - 2
Exposure time
Off
Off
0
ON
Off
0.05 s
Off
ON
1.00 s
ON
ON
10 s
Note:
If the settings directly at the pyrometer should be used the pyrometer must be
switched into offline mode
Note:
At the exposure time 0 (both DIP-switches at OFF) the device operates using the
time constant 2 ms.
Note:
Longer exposure times of 0.01 sec, 0.25 sec und 3 sec may be set via PC/ interface
(set the online
Ù
offline (DIP-switch Nr. 4) to the online position before starting!).
8.5 Emissivity
(
ε
)
For a correct measurement it is necessary to adjust the emissivity. This
emissivity
is the
relationship between the emission of an real object and the emission of a black body
radiation source (this is an object which absorbs all incoming rays and has an emissivity
of 100%) at the same temperature. Different materials have different emissivities ranging
between 0% and 100% (settings at the pyrometer between 20 and 100%). Additionally the emissivity is
depending on the surface condition of the material, the spectral range of the pyrometer and the measuring
temperature. The emissivity setting of the pyrometer has to be adjusted accordingly. Typical emissivity val-
ues of various common materials for the two spectral ranges of the instruments are listed below. The toler-
ance of the emissivity values for each material is mainly dependent on the surface conditions. Rough sur-
faces have higher emissivities.
One way to determine an accurate emissivity value for a material is to make a comparison measurement.
This can be done as follows:
1. If possible, coat a portion of the object with dull black paint or carbon soot. Paint and carbon soot have
high emissivities (95%) and take on the same temperature as the object. Measure the temperature of
the painted area with the emissivity control set to 95%. Then measure the temperature of an adjacent
unpainted area of the object and adjust the emissivity until the pyrometer displays the same tempera-
ture.
2. Measure the surface temperature of the object using a contact thermometer (e.g.
Tastotherm
MP 2000
and a suitable probe) and, at the same time, measure the temperature using the pyrometer. Adjust the
emissivity control until the pyrometer displays the same temperature as the thermometer.
Record this emissivity setting (from 1 or 2 above) for future measurements of this type of surface.
Settings:
4...20 mA
0...20 mA
Settings:
Example.:
t
90
= 1s
Settings:
100%
. . .
20%
