THE INTELLIGENT MULTICHANNEL OPTICAL PYROMETERS

OPERATION PRINCIPLES

The optical pyrometer measures intensity of radiation in eight optical bands in visible and near infrared spectral regions with high sampling rate. The instantaneous temperature of radiating material is determined using a special calibration which relates the spectral emissivity of the material to its temperature and reflects the specific conditions in a plant. In the selected time interval, the resulting temperature and its related error are statistically calculated using many measurements performed within a short period of time.

Acquired information about radiation intensity in eight spectral bands is utilized for elimination of disturbances which negatively influence the accuracy and reliability of the temperature measurement in industrial conditions. In order to eliminate these effects the internal computer of the optical pyrometer performs following operations:

• recognition and analysis of the particular situation which occurred during the measurement
• optimization of the whole measuring process and temperature calculation in accordance with actual conditions (occurrence of dust and smoke between the pyrometer and emitting surface, occurence of slag islands on molten metal, accidental obstacles in the field of view, etc.)
• carrying out the corrections of measured data in accordance with the actual conditions
• statistical processing of the experimental data, evaluating the resulting temperature and its error
• assessing the status code which reflects the measurement conditions and which can help staff (the temperature is outside the expected range, signal does not correspond to the calibration curve, molten iron is/is not in the field of view, soiled entrance window, etc.)

 

The measurement of the molten iron temperature during a tap at the blast furnace plant. 20 s record of the measured raw signals (solid lines), instantaneous temperature calculated in each sample (small blue points), average temperature in the 1 s sampling interval which corresponds to the standard time constant of most measuring devices (red circles). The average temperature in the selected interval is transferred to the central computer.

DESCRIPTION

The optical pyrometer consists of an optical head and a hermetically sealed main case containing both optic and electronic units.

The optical head collects radiation from an emitting surface. Its cover is made of stainless steel with a sapphire window. A built-in optical system enables visual positioning of the pyrometer head at the measured object. The optical head can be connected to pressured air which serves for its cooling and creates an anti-dust shield of the window, if necessary.

The head is connected to the pyrometer main case by an optical cable. For use in very hard industrial conditions, the optical cable can be protected by a hermetically sealed double armored shield.

The optical unit contains a special polychromator. Electronic unit is based on a PC-compatible processor with internal software for calculation of the instantaneous temperature, the average temperature in the selected interval and for evaluation of the experimental error. The algorithm of temperature calculation is optimized according to the specific conditions in the plant with respect for the measured material, temperature range, minimization of disturbances occurring during the measurement, special demands of time sampling, output data format, etc.

The optical pyrometer can be connected to the central computer via the serial port. The device can operate either in a self-controlled mode, i.e. periodically sending experimental data within a specified time period, or it can be controlled by a supervising computer. In the latter case, the temperature evaluation follows commands coming from the central computer. Simultaneously with the temperature value, status codes are sent to the central computer. The construction of the optical pyrometer enables its remote recalibration.

UTILIZATION OF THE MULTICHANNEL OPTICAL PYROMETERS

Described approach to measured data processing makes it possible to automatically eliminate disturbing signals occurring in the industrial conditions and enables to use the pyrometer in situations when standard one- or two-channel pyrometers do not give reliable results:

• measurement of unstable or moving objects - molten metals in steelworks, blast furnaces, foundries, etc.
• measurement of objects with islands of different temperature and/or emissivity on their surface (e.g. slag islands)
• measurement in environment with varying observation conditions (dust and smoke gusts and other obstacles to clear observation, intensive light sources, decreasing transmittance of the entrance window, etc.)
• measurement in technological plants with "aggressive" environment (heat emission, vibrations, dust, hot metal drops, etc.)
• measurement which may be influenced by unintentional and/or intentional interference with the pyrometer operation.

 
 

The measurement of the molten iron temperature during a tap at the blast furnace plant. Red crosses represent the temperature data measured by the optical multichannel pyrometer. Blue circles are the results of the reference measurements using contact termocouple probes.

INSTALLATION OF THE OPTICAL PYROMETER

To ensure the full and reliable function of the multichannel optical pyrometer we perform the following steps before and during the installation:

• modification of all technical parameters according to the specific condition in the plant
• selection of suitable place for temperature measurement and installation of the optical pyrometer
• calibration of the optical pyrometer in the selected place for specific material, temperature range, including calibration measurements in condition influenced by disturbances
• optimization of the algorithm of the temperature calculation according to the results of calibration measurements and regarding to the elimination of the disturbations
• modification of the time regime of the measurement according to user demands
• connecting the optical pyrometer to the central computer

According to the special user requests we can provide:

• special equipment for use in very hard environmental conditions (armored shields, pressure air cooling and cleaning, special windows, antidust shields, etc.)
• software for the central computer (e.g. for the data processing)

After the installation we ensure:

• modification of technical parameters according to the additional demands (reinstallation in other plants, etc.)
• regular calibrations of the pyrometer (verifying the current calibration, recalibrations for new material, etc.)
• periodical service of the pyrometer (inspections, cleaning, repairs)

TECHNICAL SPECIFICATION

All the parameters can be modified according to user's requests

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