Accuracy of a guarded hot plate (GHP) in the temperature range between -160°C and 700°C
A. Schindler, G. Neumann, D. Stobitzer and S. Vidi
Presented in this work are measurements of the thermal conductivity of insulation materials in the temperature range between -160°C and 700°C using the GHP (guarded hot plate) technique. The samples investigated are the reference materials IRMM-440 (IRMM = Institute of Reference Materials and Measurements ) and NIST SRM 1450D (NIST = National Institute of Standards & Technology ) certified in the limited temperature interval between about -10°C and 70°C, calcium silicate type SilCal1100  and expanded glass granulate . All samples cover a range of temperature-dependent thermal conductivity values between 0.013 W/(m·K) and 0.16 W/(m·K). The experimentally observed accuracy of about ±1% at room temperature and ±5% at minimum and maximum temperatures, respectively, is in agreement with combined standard uncertainty values (coverage factor k = 1) for the type  GHP and measurement conditions applied. The results on SilCal1100 and expanded glass granulate – both candidates for a standard material for insulating materials at high temperatures – are compared with previous results from recent interlaboratory comparisons [6,7].
Keywords: thermal conductivity, guarded hot plate, GHP, insulation materials