Introduction
The Phosphine (PH3) Calibration Station is a device developed by Centaur Technology Labs, that aims to facilitate the frequent testing of PH3 sensors against gases of known concentrations. This procedure aims to improve the precision of the sensors since it will contribute to the characterization of any possible drift in the sensitivity and/or the readings of the sensing elements.
The Calibration Circuit
The PH3 Calibration Setup is a gas circuit employing high-quality components, like Teflon tubes and stainless steel connectors and valves, to ensure maximum durability against a highly-corrosive gas, like phosphine. The circuit is equipped with two precision regulators to ensure a steady gas flow of 0.5 ~ 0.9l/min to the sensor hood.
The schematic of the circuit is presented below:
Notice: The circuit can support one or more sensor hoods in series, on which the user can attach the sensors to be tested. Moreover, the setup can accommodate PH3 gases at several concentrations (e.g. 500, 1000, and 2000ppm). Due to the toxicity of phosphine, it is advised to keep a safety monitoring device open in the room while running a test and make sure the room is well-ventilated.
Calibration Steps: The creation of calibration set points
The next steps will guide you through the whole procedure of testing a sensor and getting the readings of the sensor against a PH3 gas of known concentration (e.g. 500 ppm, 1000 ppm, or other):
Activate your gateway and sensors and create a new process to start collecting data from the units you plan to calibrate.
See how to set up your gateway, activate, and discover your sensors
How to create a new process - Use a name that contains the word "calibration" and the date it was started.
Unscrew the cover on the calibration station, remove the top sensor cover, and fix the sensor on the sensor hood.
Open the air source valve and set the precision valve (Vernier) at 0.5 ~ 0.9l/min into the circuit to expose the sensors to fresh air.
Open the phosphine gas valve, leaving phosphine flow towards the exhaust (i.e. not flowing in the sensor’s area).
When phosphine flow stabilizes at 5 ~ 9l/min, cross-fade between the two valves (air and phosphine) to expose the sensors to the gas.
Expose the sensor(s) to the gas for at least 5 minutes, watching the graphs on the Centaur platform.
When the sensor readings line shows a plateau, let the gas flow for another 30 seconds.
Shut off the phosphine source and open the air valve again to flush the circuit.
Watch the degassing process of the sensor going back to zero ppm*.
Repeat steps 3-9 for calibration against more than one phosphine concentration.
Create sensor calibration tables on the Centaur platform and repeat the process to verify the new, freshly-calibrated, sensor performance.
This is how a graph process looks like during the calibration of a sensor. In this example we calibrate the sensor against 2 concentrations:
*After exposure to high phosphine concentrations, it can take several minutes for a sensor to report zero ppm. For simplicity, we assume that a sensor has zeroed down when we have several readings in the area <15ppm.
Submitting the Newly-calibrated Devices to Centaur
After completing the calibration procedure against gases of known concentration(s) you need to submit the information for inspection to the Centaur team. After the data are validated, you will receive your calibration certificates.
Submit your information following this link:
