Calibrating in Accordance with ISO 27891

Regardless of the application for which you use your Condensation Particle Counter (CPC), a calibration in accordance with ISO 27891 ensures that you’re positioned to collect data of the highest accuracy. ISO 27891 specifies requirements for every portion of the calibration setup, from the generation of the primary aerosol through to the maintenance of the reference unit.

TSI has the instrumentation and knowledge to support you in your efforts to conduct calibrations (or validations) of CPCs in accordance with this standard.

Key Questions

Building a calibration setup that can be used to conduct calibrations in accordance with ISO 27891 hinges on just a few key questions:

• What calibration aerosol sizes are you interested in?
• What calibration aerosol compositions are you interested in?
• What type of reference instrument would you like to use (CPC, or electrometer)?

Aspects of an ISO 27891 Calibration Setup

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 to be present 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.

Contact TSI to discuss your calibration needs; we can recommend the specific set of instruments appropriate for your interest.