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Installation

Package Contents

The NAIS instrument package typically includes the following items:

  • The NAIS
  • Sample inlet and exhaust plugs
  • Sample inlet muff with grid
  • Spare corona needles (10 pieces)
  • Power cable
  • Ethernet cable
  • Transport box

Unpacking and Packing

The NAIS instrument is delivered in a padded flight case type box. Always use this original box for transport, as it provides optimal protection, especially when handled by delivery services.

The NAIS weighs approximately 60 kg. Always lift the instrument using the designated metal handles with at least two people. After removing it from the transport box, place the NAIS upright on a flat, level surface.

During transport and extended periods of inactivity, keep the protective covers on the instrument's inlet and exhaust tubes.

Instrument Placement

Place the NAIS on a firm, level, and non-vibrating surface. While the instrument can tolerate some vibration during measurements (e.g., in an aircraft or automobile), any vibration will increase the noise level of the measurements.

Inlet Considerations

The design and configuration of the inlet tube are crucial, as they can significantly impact the quality of NAIS measurement results. Poor inlet design can lead to increased particle losses and allow contaminants like insects, dirt or water to enter the instrument.

For the particles in the size range of the NAIS, especially below 3 nm, the main cause for particle losses is diffusion. Particle diffusion losses are minimized under laminar flow conditions and small residence time in the inlet tube.

Consider the following guidelines for the inlet tube:

  • Length: Keep the inlet tube as short as possible so that particles will not have time to diffuse to the tube walls. While turbulence increase losses, a short tube with some mixing may still result in lower overall losses than a long tube with perfectly laminar flow. If the inlet tube exceeds 1 meter, consider particle loss estimates before interpreting data.

  • Diameter: The recommended inner diameter for the inlet tube is approximately 30 mm.

  • Inner Surface: The tube interior must be smooth; avoid corrugated tubes.

  • Conductivity: The inlet tube must be electrically conductive to prevent the accumulation of static charge. Additionally, it is recommended to use a material that does not easily corrode, accumulate dirt, and has a smooth inner surface. Use a metal pipe or a suitable conductive rubber hose.

  • Insect and Dirt Protection: For outdoor measurements, place a metal mesh (1-2 mm cell size) at the end of the inlet tube to prevent insects from entering.

  • Rain Protection: Prevent rain from entering the instrument. Adjust the inlet angle as needed, or add a downward-pointing bent tube to the end of a horizontal inlet.

The mobility analyzer is sensitive to contaminants (e.g. insects, hairs, pollen). These can deposit on the electrodes, leading to increased electrical noise and parasitic currents. This is especially critical in the further end of the mobility analyzer where the gap between inner and outer electrodes becomes narrower and the central electrode voltage increases.

Temperature and Water Condensation

Critical Warning: Water condensation inside the NAIS can cause severe damage to the instrument. This risk is highest when the instrument's temperature is lower than the sample air, particularly in hot and humid climates where the NAIS is in an air-conditioned room and sampling air from outside. This situation must be avoided.

If preventing a negative temperature difference between the instrument's environment and the outside sample air is not possible, it is recommended to:

  • Place thermal insulation around the NAIS.
  • Avoid direct airflow from air conditioning units onto the instrument.

The measurement software provides a warning if a negative temperature difference is detected between the instrument body and the sample air. However, the absence of this warning does not guarantee safe operating conditions. Users must independently assess the situation to prevent condensation.

Power Connection and Grounding

The NAIS instrument uses a standard C14 power plug and operates with 110V to 240V AC 50Hz line voltage. Its average power consumption is typically below 100 W, with brief peaks up to 150 W during blower startup.

Proper electrical grounding of the NAIS is essential. An improper or missing grounding connection can:

  • Leave the instrument's body at an electrical potential, posing a risk of electric shock to the user.
  • Significantly increase particle losses.
  • Increase noise in measurement results.