Have you ever been on a site where your PID’s output value continues to climb, even in clean air? This is common in high humidity, and after long-term use.
This occurrence may lead you to ask, “What value should I record as my screening value? Should I submit this soil sample to the lab? Are any of my readings accurate?”
There are a couple of common causes for false positive readings; either a dirty hydrophobic filter (water trap) or a dirty lamp and detector combined with high humidity.
Good news, the PID is not broken. Here’s what you need to do.
1. First, swap the external hydrophobic filter. If the readings remain unstable, continue to step 2.
2. Take the instrument into a low humidity environment with clean ambient air.
3. Make sure the instrument is on and warmed up for at least 5 minutes.
4. Zero the PID in clean air and calibrate with fresh span gas..
5. Loosely cup your hand (clean hand) around the end of the probe.
If the PID indicates a steady increase in readings in excess of 10 ppm after about 15 seconds, then your lamp and sensor may be dirty and need cleaning prior to continued field use. Keep in mind that Methanol is required to clean the lamp and detector in the field and should be performed in accordance with the manufacturer’s recommendations.
6. Call your local Pine office with any questions or concerns.
For more information on moisture and its impact on PIDs please view the following technical note provided by RAE Systems:
http://www.raesystems.com/~raedocs/App_Tech_Notes/Tech_Notes/TN-163_MiniRAE_2000_Moisture.pdf
Pine Environmental Services, Inc.