Before the MiniRAE 3000 came on the market, Enviro Equipment, Inc. would often receive calls from customers wondering why their PID readings on their MiniRAE 2000 were so high when they were not expecting contamination to be present. The culprit turned out to be high humidity which can drastically affect the readings on a MiniRAE 2000, especially if the white sensor block has been fouled by frequent use without routine cleaning.
We used to tell customers that one way around this problem (not in the MiniRAE manual) was for them to test how much humidity is affecting their field readings by cupping their hands (without gloves) over the probe for about 10 seconds. The PID levels will rise quickly (a few ppm or more per second) if your sensor block is dirty. During this test it is normal for the readings to climb but at a much slower rate with a clean sensor block. The MiniRAE 2000 requires humidity filtering tubes in high humidity environments. One issue with the humidity tubes is that they can liquefy if they are not changed regularly (see Figure #1) which can cause major issues with the equipment if the liquid were to be pumped into the PID.
Figure No. 1
Thankfully, the MiniRAE 3000 introduced a built-in humidity and temperature sensor to compensate readings for humidity levels. This feature not only saves the headache of wondering why the PID readings are higher than expected, it also saves one money by not requiring humidity filtering tubes. The cleanliness of the sensor block can still affect your readings with humidity on the MiniRAE 3000 meter, although not quite as much.