The detector has three electrodes which are very close to each other. If no filters are used dust, lint or small particles can get lodged between the electrodes. When the sample air is humid the particles will conduct electricity and you can see a reading that rises slowly but steadily and keeps on going. The dust can easily be cleaned by removing the lamp and liberally blowing clean compressed air into the detector. Consult an up to date user manual for instructions.
Alternatively, we have developed an internal filter which may be inserted to minimise ingress of particles. For further information contact Ion Science.