Humidity Issues Associated with PID and how ION Science Overcome them
Water vapour and humidity is present in ambient air and can reduce PID response. In the past, this was a major limitation to the use of Photo Ionisation Devices (PIDs)
Effects of High Humidity
Like many sensors and measurement instrumentation, traditional PIDs can indeed be affected by the environmental conditions i.e. dust, dirt and in particular, humidity. The major producers of oil & gas are located in the Gulf States and in or close to the Gulf of Mexico, which are (of course) areas of high temperature and high humidity.
Solving the Problem of Humidity
Conventional PIDs may use humidity suppression/compensation techniques but each of them has disadvantages:
• Humidity sensor – these typically have a slower response than the PID sensor itself which causes a drifting compensation
• Desiccant tube – these both slow the PID response and also reduce it by adsorption plus they need replacing from time to time which adds cost
• Humidify the calibration gas – this only works at one level of humidity and is no longer accurate when the humidity changes
Importantly none of these solutions solves a false positive at high humidity
Maintenance and Purchase Considerations
To prevent dirt from entering the instrument which can contaminate the PID sensor’s lamp, there should be an easily accessible filter which can be visually inspected and changed as required. During factory calibration and maintenance, the manufacturer should also clean the PID sensor lamp and the electrode stack should be changed prior to factory recalibration which will bring the instrument back to the manufacturer’s original specification.
In daily use manufacturers recommend field calibration of their PIDs with Isobutylene, which is an excellent surrogate calibration gas because the response of most VOCs is reasonably close to, and consistent with this gas. It is also inexpensive and easily obtainable.
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White Paper Article
Everything you need to know about Humidity Issues Associated with PID and how ION Science Overcome them
Our White Paper Article is available to download below, the information provides you with key information regarding how Humidity sensors typically have slower response than the PID sensor, causing a drifting compensation. Although newer RH sensors are faster, the humidity effect varies from sensor to sensor so that the compensation algorithm causes different units from the same manufacturer to over-or under-compensate. Desiccant tubes are an added cost, slow the PID response, and can reduce the response by adsorption, especially of heavier compounds.
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