In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

Summary

This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Abstract

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

Introduction

Process control and quality assurance of objects processed in conveyor belt furnaces¹ is important and accomplished by measuring the surface temperature of the object. Currently, the temperature is typically measured by a thermocouple¹. As thermocouple measurements require contact with the object, thermocouples inevitably damage the object. Therefore, it is common to choose representative samples of a batch for temperature measurements, which are not further processed since they become damaged. The measured temperatures of these damaged objects are then generalized to the remaining samples from the batch, which are furth....

Protocol

1. Installation of IR camera into a conveyor belt furnace

1. Decide which part of the furnace should be measured by the IR camera.
   NOTE: Here, the peak zone of the firing process is chosen (see the orange highlighted zone in the firing area of Figure 1A).
2. Define the temperature range of interest that the IR camera should detect (e.g., 700−900 °C, the typical peak temperature range of the firing process).
3. Determine, or at least estimate (through experiments or literature), the temperature, spectral, and angular dependent emissions of the object(s) of interest (e.g., silic....

Results

As shown in Figure 3B−D, the example object (here, a silicon solar cell; strictly speaking, a passivated emitter and rear cell [PERC]¹²; Figure 2A,B) can be clearly detected by the IR camera in different configurations⁴. The different configurations are monofacially metallized (Figure 3B), bifacially metallized¹³ (

Discussion

Commonly, thermography temperature is corrected via measuring and adapting the optical parameters of the object, transmissive window and path, and environmental temperature of the object and transmissive window². As an alternative method, a temperature correction technique based on thermocouple measurements is described in this protocol. For the latter method, knowledge of the parameters mentioned above is not required. For the application shown here, this method is sufficient. However, it cannot .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Datalogger incl. Thermal barrier	Datapaq Ltd.
IR thermography camera "Image IR 8300"	InfraTec GmbH
IR thermography software "IRBIS Professional 3.1"	InfraTec GmbH
Solar cells	Fraunhofer ISE
Solar firing furnace "RFS 250 Plus"	Rehm Thermal Systems GmbH
Sheath thermocouples type K	TMH GmbH
Thermocouple quartzframe	Heraeus Noblelight GmbH