These can manifest as follows:
a) Sudden or erratic changes in meter display (or data logging/recording device), lasting a few seconds or less
b) Erratic changes in meter display (or data logging/recording device) which repeat at fixed intervals at certain times of day
c) Over-range or under-range indicated on meter (or data logging/recording device) lasting for long periods. [Excluding when sensor is first installed or batteries changed.]
Electrochemical and purely electronic devices can both fall victim to RFI. Fortunately, precautions can be taken to minimize RFI. It is prudent to make yourself aware of RFI sources within the monitoring environment.
Machinery with large motors or welders can produce RFI signals. Light sources such as large neon and fluorescent can be a source of RFI. Service crews could be using communications devices (two-way radios) which use RF. Monitoring at times when communications devices are being used, and comparing readings at periods of non use can determine if RFI truly is an issue.
Grounding is a means to minimize RFI. Fixed monitors should be checked to make sure the round ground lead has not been damaged or removed at the AC wall plug. Direct wiring must have a ground lead (usually green). Portable monitors can have the metal case connected to an earth ground or cold water pipe within the area. Note that grounding wire should be kept to a minimum length. Long grounding wires can have the reverse action and act as antennas.
Different enclosures provide varying degrees of protection dependent on proper grounding. Fiberglass based enclosures allow the highest response to RFI. Conductive coated fiberglass protects against weak signals. Aluminum is better than fiberglass.
Note that Interscan uses a particular aluminum alloy in its portable analyzers with low levels of magnesium, to minimize sparking when used in hazardous areas (thus enhancing the intrinsic safety). Steel is the best defense against RFI. It has drawbacks in that the weight is prohibitive for use with portable monitors, and the cost is greater.
Connecting external devices such as recorders or PLCs must have the leads shielded on one end only with the shield connected to a proper ground source. Shortest ground leads are best.
Specialized RFI-shielded enclosures are available. As such, planning is also crucial to minimize RFI. These matters should be discussed with our application engineers.