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Electrometer Problems

This section addresses common issues related to the NAIS electrometers.

High Noise Level

Symptom: One or more electrometers exhibit an abnormally high noise level.

Cause: This typically occurs when contaminants like dust or insects deposit inside the analyzer. These foreign bodies can cause a corona discharge due to the high electric field, or create a short circuit between neighboring collecting electrodes or the central electrode.

High Offset Current

Symptom: An electrometer's offset current value is high (e.g., > 10 fA).

Cause: This is often related to the same contamination issues that cause high noise.

Missing or "Inf" Current Value

Symptom: An electrometer's current reading is missing (the field is empty) or displays as "Inf".

Cause: This indicates that the electrometer is saturated and constantly resetting. During normal operation, electrometers reset every few minutes to few hours, a process that takes about 10 seconds to discharge the charge-collecting capacitor.

In case the electrometer current is very high, the capacitor may saturate again before the reset cycle completes. This typically a sever manifestation of high offset current.

This may also happen in particles mode when the post-filter is not correctly adjusted and charger ions reach the analyzer saturating the first few channels. Post-filter automatic adjustment can take up to an hour. The problem should disappear automatically.

Solutions for Electrometer Problems

  1. Clean the Analyzer: The primary solution is to clean the analyzer. Refer to the Analyzer Cleaning Instructions for a detailed guide.
  2. Improve Inlet Filtration: If the problem occurs frequently (e.g., every few days), install a denser mesh screen at the instrument's inlet to prevent contaminants from entering.
  3. Diagnose the Electrometer: If the problem persists after multiple cleanings, the electrometer itself may be faulty. To confirm this, swap the problematic electrometer with one that is functioning correctly. If the issue follows the electrometer, it is likely broken. In this case, contact Airel Support for further instructions.