12 Sensor Technology
THE MULTIPLE ATMOSPHERE CONTROLLED ENVIRONMENT (MACE): ADVANCED TYPE TESTING FACILITY FOR GAS SENSORS
INTRODUCTION In recent years, there has been a surge in emergent technologies, particularly concerning gas sensors, which can complement traditional reference grade instrumentation. Realizing this potential depends on eff ective performance evaluations of such technologies, building confi dence in their adoption for air quality monitoring strategies. In response to this trend, the European Committee for Standardization (CEN) has recently published a Technical Specifi cation (CEN/TS 17660-1:2021) addressing the requirements for such performance appraisals in laboratory tests and fi eld co-location studies. Furthermore, this specifi cation has now been incorporated as a UK MCERTS standard. In response, NPL has recently developed the Multiple Atmosphere Controlled Environment (MACE), a type testing facility conceived to assist industry in developing new products to meet the monitoring requirements of Air Quality legislation. A wide range of gas pollutant concentrations may be introduced and monitored under controlled environmental conditions in advanced purpose-built exposure chambers designed to evaluate the performance of low cost gas sensors.
MACE capabilities
The MACE facility consists of up to six state-of-the-art exposure chambers and a gas delivery system to deliver advanced testing and performance evaluation under different experimental regimes. Traceable gas compositions are generated and controlled via a gas mixing unit, which dynamically combines multiple gas sources to deliver the desired concentrations. A vaporizer unit generates humidifi ed gas streams covering the entire range of relative humidity that is in representative conditions for ambient air monitoring applications. Specialised exposure chambers with low internal volume can be used simultaneously to expose the instrumentation undergoing assessment to the generated atmospheres. These chambers are located in a temperature-controlled environmental room, which is capable of reproducing real world temperature conditions. A suite of reference grade instrumentation enables continuous measurements of the conditions being generated, such as gas composition, temperature, relative humidity and pressure. Figure 1 shows three of six exposure chambers of the MACE facility accommodating air quality sensor systems for testing.
O compositions (ppm) measured by a reference grade gas analyser sampling from one of the MACE exposure chambers.
Figure 2: Results of the CO2 H2
The facility has been designed to house sensors measuring the regulated compounds NO2
, NOx molecules including CO2 , NH3 , O3 , CO, SO2 and volatile organic compounds
(VOCs). A number of research and development projects, as well as bespoke measurement services, have been supported by the MACE facility in the recent past. One of such projects, entailed the validation of low-cost carbon dioxide (CO2
multipoint calibration. Time series of CO2
and
, together with other
) sensors
with respect to temperature and response to water vapour. The following section focuses on the diagnostic results measured by calibrated reference quality instrumentation employed to showcase the performance of the MACE facility. The proprietary results obtained from the low cost sensors under evaluation have not been included.
Case study: validation of carbon dioxide (CO2
) sensors
Water vapour is likely to cause cross-interference in carbon dioxide measurements by optical (NDIR) sensors. To support industry in improving the performance of CO2
sensor systems,
NPL has deployed the MACE facility to generate empirical evidence for the effects of absolute humidity, relative humidity and temperature on the performance of these sensors. The whole programme of work entailed a number of exposure regimes, three of which are highlighted below. The full set of results is being used to enable improvements in the proprietary compensation algorithms used for CO2
low cost sensors. The initial example is a multipoint calibration of CO2
Figure 1: Photograph showing three of the exposure chambers of the MACE facility.
, which had
the objective of establishing traceable calibration factors for the sensors’ response this gas. The target conditions were four
IET MARCH / APRIL 2023
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
