© NMISA 2010 INTERNATIONAL ACTIVITIES AT THE NMISA HUMIDITY LABORATORY DURING 2009/2010 Deona Jonker

© NMISA 2010 Introduction Need for traceable measurements in the temperature range 5 °C to 55 °C (humidity range 10 %rh to 95 %rh) Saturated and unsaturated salts provide traceable measurements only over temperature range of 15 °C to 30 °C Bilateral comparison between NMISA and Mikes (Finland) – compare relative humidity calibration capabilities over temperature range 5 °C to 55 °C and humidity range 10 %rh to 95 %rh

© NMISA 2010 Introduction (continued) NMISA two-pressure generator used in follow-up measurements to investigate results of bilateral comparison Two posters presented by NMISA at Tempmeko–ISHM 2010 symposium

© NMISA 2010 NMISA – MIKES Bilateral Comparison Comparison arrangements and measurements Five thermohygrometers used in comparison Comparison range: Humidity – 10 %rh to 95 %rh Temperature – 5 °C to 55 °C; 10 °C intervals (six temperature points) Calibrations at MIKES: By comparison with chilled mirror hygrometers in climatic chamber

© NMISA 2010 NMISA – MIKES Bilateral Comparison (continued) Constant temperature; rising humidity; air flow over sensors Calibration at NMISA: In small 100 ml chambers placed in large temperature- and humidity-variable chamber Against reference unsaturated salt solutions Metal filters not removed from sensors No air flow over sensors Constant humidity and rising temperature

© NMISA 2010 NMISA – MIKES Bilateral Comparison (continued) MIKES measured transfer standard set before and after initial measurements at NMISA MIKES compiled comparison report Comparison results: Results obtained with fifth hygrometer (MI70) agreed fairly well at most of measurement points Transfer standard set showed non-linearity in high humidity range and few other points

© NMISA 2010 NMISA – MIKES Bilateral Comparison (continued) Possible reasons: Metal filters over sensors should been removed when measuring in static conditions (no air flow) Using the same salt solution at different temperature points

© NMISA 2010 NMISA – MIKES Bilateral Comparison (continued) Follow-up measurements: to investigate the influence of metal filters on sensors Use same 100 ml chambers placed in temperature- and humidity-variable chamber Measuring points: 10 %rh at 5 °C and 15 °C 50 %rh at 25 °C and 35 °C 90 %rh at 45 °C and 55 °C Unsaturated salt solutions as reference standards

© NMISA 2010 NMISA – MIKES Bilateral Comparison (continued) No air flow over sensors Metal filters removed from sensors Results - influence of metal filters much more significant for transfer standard set than for fifth hygrometer (MI70) Good laboratory practice to remove filters from sensors during calibration

© NMISA 2010 NMISA Two-Pressure Generator Design and improvements made Generator originally consisted of: Saturator – 0.9 m long, made of one inch diameter, stainless steel tubing 70 L stirred bath Air bath – to control temperature of test chamber Compressed air supplied to mass flow controller to saturator through heat exchanger coil (app. 1.6 m) to T-piece

© NMISA 2010 NMISA Two-Pressure Generator (continued) to chilled mirror dew point meter and test chamber for relative humidity measurements Pressure and temperature were constantly monitored Initial design of generator lacked sufficient and proper temperature equilibrium and air saturation Modifications: Add second liquid bath with independent temperature control

© NMISA 2010 NMISA Two-Pressure Generator (continued) Bath contains heat exchanger coil (6 m long, made of 6.35 mm diameter stainless steel tubing) and pre- saturator coil (1.45 m long, made of 25.4 mm diameter stainless steel tubing) Bath placed between mass flow controller and saturator bath Heat exchanger coil removed – caused leak in system Dry air to mass flow controller – to pre-saturator – to main saturator (no heat exchanger) Air bath replaced with temperature-variable chamber

© NMISA 2010 NMISA Two-Pressure Generator (continued) Follow-up measurements: to investigate air flow over sensors Generator used to investigate influence of air flow over sensors during calibration Generator outlet connected to small stainless steel chambers, connected in series Small chambers placed in large temperature- and humidity variable chamber Flow rate over sensors app. 0.5 l/min

© NMISA 2010 NMISA Two-Pressure Generator (continued) Measurements performed at 5 °C; 25 °C and 55 °C At each temperature point – humidity measurements at 10 %rh to 95 %rh and back to 10 %rh Measurements with two-pressure generator agreed much better with MIKES’ results for transfer standard set than did NMISA’s initial measurements

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 1. Results of the laboratories obtained with the transfer standard set at +5 °C. Error bars show the estimated expanded uncertainty.

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 2. Results of the laboratories obtained with the transfer standard set at +25 °C. Error bars show the estimated expanded uncertainty. (Note: the NMISA result at 95 %rh is off scale (12.9 ± 1.2 %rh)

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 3. Results of the laboratories obtained with the transfer standard set at +45 °C. Error bars show the estimated expanded uncertainty.

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 4. Results of the laboratories obtained with the transfer standard set at +55 °C. Error bars show the estimated expanded uncertainty.

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 5. Results of the laboratories obtained with the fifth hygrometer at +5 °C. Error bars show the estimated expanded uncertainty. The long-term instability is not included.

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 6. Results of the laboratories obtained with the fifth hygrometer at +25 °C. Error bars show the estimated expanded uncertainty. The long-term instability is not included.

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 7. Results of the laboratories obtained with the fifth hygrometer at +35 °C. Error bars show the estimated expanded uncertainty. The long-term instability is not included.

© NMISA 2010 NMISA Two-pressure generator (continued) Figure 8. Results of the laboratories obtained with the fifth hygrometer at +55 °C. Error bars show the estimated expanded uncertainty. The long-term instability is not included.

© NMISA 2010 Tempmeko-ISHM 2010 Symposium Joint International Symposium on Temperature, Humidity, Moisture and Thermal Measurements in Industry and Science – Tempmeko-ISHM 2010, 31 May to 4 June 2010, Portoroz, Slovenia Two posters presented: Improvements made to the NMISA two-pressure generator Bilateral comparison of relative humidity standards between NMISA and MIKES

© NMISA 2010 Tempmeko-ISHM 2010 Symposium (continued) Typical topics discussed: Development / improvement of primary humidity standards (humidity generators) Hygrometer and moisture sensor developments Humidity uncertainty estimations Interlaboratory comparisons Calibration procedures Calibration facilities Industrial applications of humidity measurements

© NMISA 2010 Tempmeko-ISHM 2010 Symposium (continued) Presentations on interlaboratory comparisons: Dew-point temperature realizations in the range -50 °C to +20 °C; 24 NMIs (22 EURAMET, South Africa, Russia) participated Bilateral comparison between Egypt (NIS) and Turkey (TUBITAK UME); dew and frost point temperatures over the range -40 °C to + 50 °C Comparison of frost-point temperature scales between -80 °C and -10 °C; MIKES (Finland), INRIM (Italy), LNE-CETIAT (France) participated

© NMISA 2010 Tempmeko-ISHM 2010 Symposium (continued) Presentations on humidity standards: NIST presented paper on their newly developed second-generation gravimetric hygrometer and steam generator National Metrology Institute of Japan (NMIJ) established primary humidity standard in trace moisture region using diffusion tube method New primary low- and high-range dew-point generators developed by Croatian NMI in cooperation with MIKES

© NMISA 2010 Tempmeko-ISHM 2010 Symposium (continued) Paper on psychrometer comparison between NMIs Denmark, Slovenia, Finland Paper on homogeneity and stability of humidity test chambers Measurement of moisture content in materials: New facility at NPL (UK) INRIM (Italy) investigating traceability of moisture content in wood