Imaging phosphor thermometry from T  =  20 °C to 450 °C using the time-domain intensity ratio technique

Abstract

We present an imaging phosphor thermometry system using the time-domain intensity ratio technique and demonstrate surface temperature measurements that are traceable to ITS-90 with a calibration Standard uncertainty of 0.5 °C, over the range 20 °C to 450 °C. The thermographic phosphor used was Mg 4 FGeO 6 :Mn. Typically, imaging phosphor thermometry systems make use of the intensity ratio of the phosphor emission in two discrete wavelength bands, measured simultaneously using two cameras viewing the same surface. However, difficulties can arise with image registration (the requirement to spatially align the two images) due to lens distortion, non-normal viewing angles and camera alignment, and this can result in large temperature errors. The time-domain intensity ratio technique presented here avoids these difficulties by capturing two images at different times during the phosphorescence decay process using a single monochrome camera. Each pixel of the camera integrates the light collected over the exposure time. By careful selection of an appropriate exposure time, along with the timing of each exposure (image gating), it is possible to collect two specific time integrated portions of the phosphor decay curve. The phosphor decay time can then be calculated quickly and uniquely from the ratio of these two signals and related to the temperature through calibration. With this technique, there is no requirement for high framerates and satisfactory results can be obtained using a relatively inexpensive camera provided that suitable triggering and exposure control are available. Here, we provide a description of the technique, the instrumentation, calibration, and preliminary measurement made on a resistively heated steel coupon, where the standard uncertainty for a single imaged pixel (80 μm × 80 μm) was 7.7 °C, 6.6 °C and 3.8 °C at temperatures of 200 °C, 300 °C and 400 °C respectively. Additionally, a sensitivity analysis and an uncertainty budget are provided.

Relating micro-segregation to site specific high temperature deformation in single crystal nickel-base superalloy castings

“…The maximum stress prior to hardening is,  = 12.3 MPa; accordingly, creep tests were carried out in the temperature range; 1300C to 1240C for a range of stresses up to a maximum value of 12 MPa. In the cooling experiments for a cooling rate of 0.1 C s-1, the time duration for a decrease in temperature by 10 C is 100 s; therefore, creep at any stress was conducted for a maximum time interval of 100 s. This is in sharp contrast to that reported in other studies [23]. Table 6, the strain induced is underlined, as in Table 5 for flow stress.…”

“…Water-cooled grips are used to give a temperature gradient along the length of the sample [21,22]. Recent studies have confirmed that at a central temperature up to around 900C, the temperature distribution along the test-piece is parabolic [23,24]. Consequently, the temperature variation along the 3 mm gauge length for Ni-base alloys is typically 5C [25].…”

Imaging Luminescence Thermometry to 750 °C for the Heat Treatment of Common Engineering Alloys and Comparison with Thermal Imaging

“…Imaging luminescence thermometry can be implemented for both decay time and intensity ratio techniques. In our previous work [12] we presented an imaging system based on the decay time method, where three images are captured with a single camera at different times after extinction of the excitation light: 1) immediately following extinction, 2) a fixed time after extinction and 3) once all luminescence has ceased (background measurement). We refer the reader to the publication for full details.…”

“…Thermographic phosphors exhibit a change in their temporal or spectral luminescence properties during or following excitation with UV or near-UV light. For a comprehensive summary of phosphor thermometry, we refer the reader to the review articles [9][10][11], with details of our earlier work given in [12]. Here we confine ourselves to the basic principles of the two most common phosphor thermometry techniques: decay time and intensity ratio.…”

Self‐Referenced Temperature Imaging with Dual Light Emitting Diode Excitation and Single‐Band Emission of AVO4:Eu3+ (A=Y, La, Lu, Gd) Nanophosphors

“…[14] However, slower measurements can also be performed by changing the excitation pulse-exposure delay between consecutive pulses. [15][16][17] Based on the time domain, this approach has the advantage of robustness against spectral DOI: 10.1002/adpr.202100139 Luminescence thermometers exhibiting ratiometric response in their emission spectrum are widely investigated but to obtain two-dimensional measurements, either the emission spectrum must be slowly scanned over the area of interest or the emission decomposed using two separate detector arrays with spectral filters.…”