To achieve the highest accuracy in your Condensation Particle Counter (CPC) data collection, it’s essential to follow the calibration requirements outlined in ISO 27891. This guide will help you navigate the key components of an ISO 27891 calibration setup, addressing critical questions regarding aerosol sizes, compositions, and reference instruments to ensure you are well-equipped for precise measurements.
Aerosol Generation and Conditioning
Electrospray aerosol generation is required, for its ability to create a quasi-monodisperse aerosol. The shape of the particle size distribution as created by an electrospray aerosol generator is ideally suited for subsequent classification into a highly monodisperse calibration aerosol that contains very few multiply-charged particles.
Electrospray Aerosol Generators (EAG) from TSI® include the EAG 3480 and EAG 3482.
Aerosol Size Classification
After the primary aerosol is generated via electrospray, it must be classified to produce the monodisperse aerosol with which the Unit Under Test (UUT) and Reference Unit will be challenged; this is often referred to as a “calibration aerosol.”
The calibration aerosol is required to be highly monodisperse, and to contain a population no larger than 10% of particles that carry multiple charges. A Differential Electrical Mobility Classifier (DEMC) is specified to be used; a common industry term for this technology is Differential Mobility Analyzer (DMA).
TSI has two models of Differential Mobility Analyzers (DMA) well-suited for creating classified calibration aerosol; the “Long” DMA 3081A, and the “Nano” DMA 3085A. Both are controlled using an Electrostatic Classifier 3082.
In order for the size classification to produce accurate results, an aerosol neutralizer is required; both radioactive (3077A) and soft x-ray (3088) models are available.
Characterizing the calibration aerosol for multiply-charged aerosol can be done using a mathematical method, or it can be done by measuring the size distribution of the calibration aerosol. TSI’s Scanning Mobility Particle Sizer™ (SMPS™) is an ideal tool for characterizing monodisperse calibration aerosols.
Flow Handling
The calibration aerosol is contained within a certain volumetric flow rate of air. This flow may not match the total flow required by the UUT and the Reference Unit. A make-up or bleed flow step is required in the setup. Prior to splitting the flow between these two instruments, a mixer is used to ensure that the aerosol is well-mixed across the cross-sectional area of the tubing carrying the calibration aerosol to the location where it is split between the two measurement instruments.
Splitting calibration aerosol flow into as many as four branches can be done easily using the Flow Splitter (4-way) 3708.
Reference Instrumentation
ISO 27891 provides a choice of reference instrument: a CPC may be used, or a Faraday Cage Aerosol Electrometer may also be used. In either case, the standard provides requirements pertaining to the calibration, operation, and maintenance of the reference unit.
The CPC 3750 and Aerosol Electrometer 3068B are both widely used as reference instruments in a variety of calibration settings.
Calibrating a CPC in accordance with ISO 27891 provides a very high level of confidence in the accuracy of the instrument. If your calibration interests also include performing calibrations or validations outside of ISO 27891 (for example, calibrating Engine Exhaust CPCs with soot aerosol), TSI is your calibration partner.