How Qube’s Auto-calibration Technology Ensures Consistent Leak Detection Performance
Author: Adrian Dumitru and Dave Levy
Metal oxide sensors can drift from their calibrated responses over time. But Qube’s auto-calibration process runs continuously and autonomously to identify potential sensor drift and correct itself to ensure consistent leak detection performance and data integrity.
Metal Oxide Sensors and Methane Detection
Metal oxide sensors (MOS) offer a low-cost, effective, and reliable method for monitoring low-level methane concentrations. Qube uses metal oxide (MOx) sensing technology because metal oxide is highly sensitive to greenhouse gasses such as methane, is relatively inexpensive to scale, can operate over a wide range of temperature and humidity, and has an extended operational life. Each MOx sensing element exhibits a unique, highly non-linear response to gasses at low concentrations.
These qualities enable operators to cost-effectively deploy the Qube platform across companywide assets for maximum emissions management results with minimal hardware costs compared to other emissions monitoring technologies.
How Qube Calibrates Its Methane Oxide Sensors
Each Qube sensor goes through a rigorous manufacturing calibration process to ensure accuracy and consistent performance. The (patent pending) manufacturing calibration process takes place in the lab where a unique gas response curve is developed for each individual sensor down to 1PPM accuracy over the operation ranges of temperature, humidity, pressure, and gas concentration.
Once deployed in the field, Qube sensors use a patented technology to continuously verify their outputs against the environmental gas background at that location (most locations have a CH4 background of 1.9 PPM).
A self-calibration is performed by scaling a sensor’s gas response curve to the environmental gas background. Gas response curves are complex formulas with a unique set of coefficients, but we have identified a subset of those which are responsible for drift.
When there is a mismatch between the environmental gas background detected by the sensor and the actual known background, a self-calibration is triggered and the subset of coefficients is adjusted so the background and actuals match.
In effect, we use the environmental background as a calibration gas during field operations. This continuous stay-in-calibration check ensures accuracy and minimizes the possibility of false positives.
The auto-calibration workflow described here is illustrated below:
Qube’s auto-calibration workflow.
Qube’s Metal Oxide Sensors Can Be Calibrated Remotely
The auto-calibration process runs continuously and autonomously to identify sensor drift. Qube can update the calibration response curves remotely, which saves operators significant time and labor that would otherwise be needed to send out a crew to do this work.
Remote calibration is especially helpful for hard-to-reach locations or across large operations where hundreds or thousands of sites may be monitored.
Qube’s remote calibration process is continually verified with lab and field testing against reference gas analyzers. Customers can monitor emissions performance and device health in real-time from anywhere in the world through Qube’s online dashboard.
Innovation Leads the Way
Although metal oxide sensors are highly sensitive and reliable, they are susceptible to drift over time due to aging and continuous exposure to the elements. In response, Qube has developed proprietary technologies and processes to preempt potential inaccuracies that baseline drift may cause by continuously monitoring device outputs against the environmental background and re-calibrating them as needed, and immediately upon detecting a potential drift from the baseline.