Using Config Mode Modus; Calibration; Calibration Set-Up - WatchGas NEO User Manual

D e t e c t i o n D e t e c t i o n
7. Using Config Mode Menus

7.1 CALIBRATION

Perform a calibration regularly. The instrument will hold its calibration, but
over time, detection circumstances change and instrument components get
contaminated, which can change the response of the instrument to detectable
gases.
Perform a bump test before each day's use. This ensures that the instrument
is fully working, especially when the NEO is used to alert users to hazardous
concentrations of gas.
When feasible, perform calibration with the gas you are going to measure most often.
A calibration performed with isobutylene is a good alternative because it shows good response on PID
instruments, is inexpensive, stable and non-toxic.
A correction factor (CF) can be applied to make the NEO display the true concentration of the gas
being measured, if you are absolutely sure that only that gas is measured. You can select the CF from
the instrument's gas library of over 200 compounds, or enter a CF manually. See Technical Note 2: PID
Correction Factors for more information.

7.1.1 CALIBRATION SET-UP

To perform a calibration, you need:
• A gas cylinder with calibration gas with an exactly determined concentration and a valid certificate
that is traceable to international standards.
• A source of clean air with 20.9 %vol of Oxygen:
• A gas cylinder with clean air in an exactly determined concentration and a valid certificate that is
traceable to international standards.
• Gas bag with clean air.
• Ambient air filtered through a charcoal tube (VOC Zeroing Tube).
• Outdoor ambient air usually contains a few ppb of VOC, and can only be used with instruments
with a resolution from 10 ppb and up.
• A flow regulator to control the gas flow from the cylinder.
• Tubing with Luer connectors to connect the gas source to the instrument.
To match the flow to the pump speed exactly, you can use a demand flow regulator. Alternatively:
• Fill a gas bag with calibration gas and connect the instrument with the gas bag when performing
span calibration.
• Use a flow regulator with a flow > 500 cc/min and let the excess flow escape through a T connector
NEO Photoionization Detector
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