Question

What is pyrometry? Explain the working of optical pyrometer with a neat diagram. State its one application.

Answer 1

### Pyrometry Overview

**Pyrometry** is the science and technology of measuring high temperatures without making direct contact with the object whose temperature is being measured. This is particularly important in industrial processes where objects are either too hot to touch or where introducing a sensor could interfere with the process.

### Working Principle of Optical Pyrometer

An **optical pyrometer** measures temperature based on the color (wavelength) of the visible light emitted by a hot object. It works on the principle that the radiation emitted by an object changes with its temperature. Specifically, as an object's temperature increases, the color of the light it emits shifts from red to yellow to white, and eventually to blue, according to Planck’s law.

#### Components of an Optical Pyrometer:

1. **Eyepiece:** Through which the operator views the object.
2. **Filament:** A thin wire of known material whose temperature can be controlled.
3. **Lens System:** Focuses the light from the hot object onto the filament.
4. **Battery and Variable Resistor:** Used to adjust the current through the filament.
5. **Calibration Scale:** Displays the temperature corresponding to the filament's brightness.

#### Working Steps:

1. **Viewing the Object:**
   The optical pyrometer is aimed at the hot object. The lens system focuses the emitted light onto the filament inside the pyrometer.

2. **Matching the Brightness:**
   The operator adjusts the current through the filament using a variable resistor until the brightness of the filament matches the brightness of the object. When this happens, the filament seems to "disappear" against the background of the object (due to the matching radiation intensity).

3. **Reading the Temperature:**
   Once the brightness is matched, the current through the filament corresponds to a specific temperature, which is calibrated and displayed on a scale. This temperature is the temperature of the object.

#### Diagram of an Optical Pyrometer:

Below is a simplified diagram of an optical pyrometer:

```plaintext
                +---------------+
                |               |
     Object --> |   Lens        | --> |  Filament   | --> Eyepiece (to view object and filament)
                |   System      |     |             |
                +---------------+
                                                
                                                
                    |                           |
                Variable                  Calibration
                Resistor                    Scale (Temperature)
                    |
                Battery (Current Source)
```

### Application of Optical Pyrometer

One common application of an optical pyrometer is in **metallurgy**. It is used to measure the temperature of molten metals in furnaces, where direct contact with a thermometer would be impractical and potentially damaging.

### Summary

In summary, pyrometry involves the measurement of high temperatures without direct contact, and optical pyrometers specifically use the principle of matching the brightness of a filament to the visible light emitted by a hot object. This technique is widely used in industries like metallurgy, where accurate and non-invasive temperature measurements are crucial.

Answer 2

**Pyrometry** is a technique used to measure high temperatures, typically without direct contact with the object being measured. It relies on detecting the thermal radiation emitted by the object. Pyrometers are commonly used in industrial processes where temperatures are too high for conventional thermometers.

### **Working of Optical Pyrometer**

An optical pyrometer measures temperature based on the brightness (radiant intensity) of the visible light emitted by a hot object. The key steps involved in its operation are:

1. **Radiation Collection**: The pyrometer collects the thermal radiation emitted by the hot object using an optical system (like a lens or a mirror).

2. **Filtering**: The collected radiation passes through a filter that isolates a specific wavelength of light. This wavelength is usually in the visible spectrum.

3. **Detection**: The filtered radiation is directed onto a detector (such as a photodetector) that measures the intensity of the light.

4. **Comparison and Calibration**: The intensity measured is compared against a reference source with a known temperature. The pyrometer is calibrated to correlate the intensity of radiation with the temperature of the object.

5. **Temperature Reading**: The pyrometer converts the measured radiation intensity into a temperature reading using established calibration curves or equations.

### **Diagram**

Here's a simplified diagram of an optical pyrometer:

```
   +--------------------+
   |   Hot Object       |
   +--------------------+
          |  
          v
   +--------------------+
   | Optical System     |
   | (Lens/Mirror)      |
   +--------------------+
          |
          v
   +--------------------+
   |   Filter           |
   +--------------------+
          |
          v
   +--------------------+
   |   Detector         |
   +--------------------+
          |
          v
   +--------------------+
   |   Display/Output   |
   +--------------------+
```

### **Application**

One common application of optical pyrometers is in **metal casting**. During the casting process, it is crucial to monitor the temperature of molten metal to ensure it is within the optimal range for forming the desired shape and properties. Optical pyrometers allow for accurate, non-contact temperature measurement, which is essential in high-temperature environments where traditional sensors might fail.