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Diagnostic Checklist

The following list of conditions can be used to check that the instrument is operating properly.

Many of these checks are also done by the measurement software and a warning will be shown if some condition is not met. But here are also several checks that can not be carried out automatically.

Electrometers

  1. Electrometer noise levels are around 0.1 fA for 10 s average records. May be 0.2 fA for electrometers number 17 and larger.

  2. Electrometer currents in offset mode do not exceed ±10 fA.

  3. Electrometer integrator output voltages are between –4 and +4 V.

  4. Electrometer integrator output voltages are different and quite random.

  5. No electrometer has resets more frequently than once every 5 minutes.

  6. The is no visible systematic drift in electrometer currents when looking at 1 s data for several consecutive measurement cycles.

  7. Check the electrometer time series plots of raw records. The fluctuations in all electrometers should be random. There should be no obvious waveform or beat pattern.

  8. Final block average electrometer currents are positive or at least not below −2σ in any operating mode.

Air Flows

  1. Barometric pressure measurement is correct within 1 hPa.

  2. All flow rate feedback controls are between 1.1 and 3.9 V.

  3. Total sample flow rate is 54 l/min. Positive and negative sample flow rates are both 27 l/min (if measured separately).

  4. Positive and negative sheath flow rates match their target values. The target is calculated from the barometric pressure to maintain constant volumetric flow, and is approximately 60 l/min at 1000 hPa.

  5. There is no audible periodic fluctuation of the flow rates, blower noise.

  6. Blowers react when obstructing the inlet or outlet with hand.

  7. Blowers return to normal after previous obstruction is removed.

  8. Airtightness: Close the inlet completely with hand and wait until the blowers have stabilized. The total sample flow rate should not exceed 10 l/min.

Sample Conditioning

  1. Charger currents are +15 to +25 nA for the positive analyzer and −15 to −25 nA for the negative analyzer in particles and alternating charging modes. In offset and ions modes, charger currents are close to 0 nA.

  2. Standard deviation of positive and negative charger currents is less than 2 nA.

  3. Positive and negative discharger currents are around 20 nA in offset mode,
    around 10 nA in alternating charging mode,
    and 0 nA in particles and ions modes.

  4. Standard deviation of positive and negative discharger currents is less than 2 nA.

  5. Pre-filter is active in offset mode.

  6. In case the charger current standard deviation parameters are not shown: check charger currents in raw records to see that they don't fluctuate more than a few nA.

Post-filters

  1. Positive and negative post-filter voltages are between 20 and 80 V in particles and alternating charging modes.

  2. Positive and negative post-filter voltages are around 0 V in ions and offset modes.

  3. Positive and negative post-filter voltages are automatically adjusted: there are small variations in the voltage for each next measurement cycle.

Sheath Air Filters

  1. There are no warnings about sheath air filter voltage fluctuations or voltage load that could indicate corona discharge in the filter.

Spectra

  1. Positive and negative ion distributions are similar to within 10% for mobilities below 1 cm2/V/s.

  2. Positive and negative particle distributions are similar to within 10% for sizes above 2.5 nm.