© NMISA 2010 THE 2009/2010 SANAS COMPARISON FOR HUMIDITY Deona Jonker

© NMISA 2010 Introduction SANAS Humidity audit was carried out during the period 6 October 2009 to 25 March 2010 Purpose of the audit – to ascertain whether each laboratory was able to perform accurate measurements within the laboratory’s accredited measurement capabilities Parameters covered: a) Relative humidity hygrometer – (11; 33; 53; 75; 90) %rh b) Saturated salt solution capsules – (11 & 53) %rh

© NMISA 2010 Comparison Arrangements Audit samples: a) Rotronic Hygrolog-D & Hygroclip S thermohygrometer b) Novasina saturated salts (SC-11 & SC-53) Participating laboratories – SANAS accredited laboratories for relative humidity hygrometers and saturated salt solutions (total of four laboratories) Laboratories received protocol before the start of the audit

© NMISA 2010 Comparison Arrangements (continued) Protocol included the following information: a) audit equipment b) timetable for measurements c) handling of the audit instruments d) measurement instructions e) reporting deadline Templates for measurements and uncertainties provided

© NMISA 2010 Measurements NMISA measured audit samples before and after audit sample cycle using unsaturated salt standards October 2009 – first laboratory performed measurements; all audit parameters were measured Second laboratory performed measurements twice (November 2009 and February 2010); measurements with thermohygrometer only November 2009 – third participating laboratory received audit samples (thermohygrometer and SC-11)

© NMISA 2010 Measurements (continued) December 2009 – NMISA measured thermohygrometer again using saturated salt standards; verified audit salt capsules

© NMISA 2010 Method of Analysing the Results Laboratories were judge on their measurement results with respect to the laboratory’s measurement capability Reference values – average of the measured values by NMISA before and after audit sample cycle Method used for the evaluation of the measurement results: calculate the error E n

© NMISA 2010 Method of Analysing the Results (continued) E n = (laboratory value – reference value)/ √(U lab 2 + U ref 2 ) laboratory value = measured value reported by the laboratory reference value = average value measured by NMISA U lab = UoM reported by the laboratory U ref = uncertainty of the reference value E n should be between limits of ±1 to ensure the error is within laboratory’s UoM |E n | < 1 were considered acceptable

© NMISA 2010 Results DateLab name Actual RH(%rh) t (°C) Actual %rh (tref) RV (%rh) U(k=2) (%rh) LV-RV (%rh) En|En|Comments 02-Apr-09NMISA MC = 0.4 %rh 07-Apr MC = 1.1 %rh Mean: Std dev:0.33 DateLab name Actual RH(%rh) t (°C) Actual %rh (tref) RV (%rh) U(k=2) (%rh) LV-RV (%rh) En|En|Comments 12-Oct-09HMD MC = 1.0 %rh 12-Oct MC = 1.5 %rh Mean: Std dev:1.30 DateLab name Actual RH(%rh) t (°C) Actual %rh (tref) RV (%rh) U(k=2) (%rh) LV-RV (%rh) En|En|Comments 22-Nov-09HMD MC = 3.0 %rh Mean:0.33 Std dev: DateLab name Actual RH(%rh) t (°C) Actual %rh (tref) RV (%rh) U(k=2) (%rh) LV-RV (%rh) En|En|Comments 11-Mar-10NMISA MC = 0.4 %rh 10-Nov MC = 1.1 %rh Mean: Std dev:0.32 Table 1. Saturated Salt Solution Capsules (SC-11 & SC-53)

© NMISA 2010 Results (continued) Figure 1. Saturated Salt Solution SC-11

© NMISA 2010 Results (continued) Figure 2. Saturated Salt Solution SC-53

© NMISA 2010 Results (continued) Table 2. Relative Humidity Hygrometer

© NMISA 2010 Results (continued) Table 2. Relative Humidity Hygrometer (cont.)

© NMISA 2010 Results (continued) Table 2. Relative Humidity Hygrometer (cont.)

© NMISA 2010 Results (continued) Figure 3. Relative Humidity Hygrometer – 11 %rh

© NMISA 2010 Results (continued) Figure 4. Relative Humidity Hygrometer – 30 %rh

© NMISA 2010 Results (continued) Figure 5. Relative Humidity Hygrometer – 50 %rh

© NMISA 2010 Results (continued) Figure 6. Relative Humidity Hygrometer – 75 %rh

© NMISA 2010 Results (continued) Figure 7. Relative Humidity Hygrometer – 90 %rh

© NMISA 2010 Conclusions and Discussion Results are, in general, satisfactory Laboratories’ calculated expanded uncertainties used in calculation of E n value Large correction factors at low and high humidity values – due to chamber leaks or stabilisation time Some laboratories quoted unrealistic small uncertainties – do not take into account all relevant sources of uncertainty