Dr Grant Forster

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Instrument Support Level 3
Instrument Support Level

Instrument Support Level 3

Manufacturer & Model

Thermo Scientific 42i

Daily Facility Charge

Not Applicable


Calendar 2:
TECO 42i NOx Monitor

TECO 42i NOx Monitor

The Thermo Scientific Model 42i Analyser is a single chamber, single photomultiplier tube design that cycles between the NO and NOx modes. The 42i Analyser has independent outputs for NO, NO2 and NOx and each can be calibrated separately. Dual range and auto range are standards features as well. If required, the instrument can be operated continuously in either the NO or NOx modes allowing for response times of less than five seconds.

Temperature and pressure correction are standard features.

User settable alarm levels for concentration and for a wide variety of internal diagnostics are available from an easy to follow menu structure.

This state-of-the-art gas analyser offers features such as an Ethernet port as well as flash memory for increased data storage. Ethernet connectivity provides efficient remote access, allowing the user to download measurement information directly from the instrument without having to be onsite. Easily programmable short cut keys allow you to jump directly to frequently accessed functions, menus or screens. The larger interface screen can display up to five lines of measurement information while the primary screen remains visible.

The Model 42i Trace Level operates on the principle that nitric oxide (NO) and ozone (O3) react to produce a characteristic luminescence with an intensity linearly proportional to the NO concentration. Infrared light emission results when electronically excited NO2 molecules decay to lower energy states. Specifically:

NO + O3 → NO2 + O2 + hν

The ambient air sample is drawn into the Model 42i Trace Level through the sample bulkhead, to the prereactor solenoid valve.

The prereactor solenoid valve directs the sample either to the reaction chamber, where it mixes with ozone to give an NO reading or to the prereactor, where it reacts with ozone prior to the reaction chamber giving a dynamic zero reading for the analyzer. The prereactor is sized so that greater the 99% of a 200 ppb NO sample will react prior to entering the reaction chamber, yet is small enough to allow other potential interferents to pass through to the reaction chamber.

Dry air enters the Model 42i Trace Level through the dry air bulkhead, passes through a flow switch, and then through a silent discharge ozonator. The ozonator generates the ozone needed for the chemiluminescent reaction. At the reaction chamber, the ozone reacts with the NO in the sample to produce excited NO2 molecules. A photomultiplier tube (PMT) housed in a thermoelectric cooler detects the luminescence generated during this reaction.

The NO concentrations calculated are stored in memory. The Model 42i Trace Level outputs NO concentrations to the front panel display, the analog outputs, and also makes the data available over the serial or Ethernet connection.

Contact Grant Forster for details.

The last 24 hours of data can be viewed here

Higher frequency data can be obtained through a request to Grant Forster.