Dr Grant Forster

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Instrument Support Level 2
Instrument Support Level

Instrument Support Level 2

Manufacturer & Model

Thermo Scientific 49

Daily Facility Charge

Not Applicable


Calendar 2:
TECO 49i Ozone Monitor

TECO 49i Ozone Monitor

The Thermo Scientific Model 49i is a powerful, easy-to-use, UV photometric based ozone analyser which offers increased specificity via its balanced optical system.

User-programmable software capabilities allow selection of the frequency at which internal zero/span activation and instrument calibration checks will occur.

Additionally, field-programmable measurement range settings can be stored in memory for subsequent recall. Extended troubleshooting diagnostics now provide an instantaneous indication of instrument operating parameters, status including Pressure, Flow, DC Supply Voltages, Optical Bench Temperature, Ozonator Power Supply Voltage, and Lamp Voltage.

The 49 Series Ozone Analysers are based on the principle that ozone molecules absorb UV light at a wavelength of 254 nm. The degree to which the UV light is absorbed is directly related to the ozone concentration as described by the Beer-Lambert Law:

I/I0 = e-KLC


K = molecular absorption coefficient, 308 cm-1 (at 0°C and 1 atmosphere)

L = length of cell, 38 cm

C = ozone concentration in parts per million (ppm)

I = UV light intensity of sample with ozone (sample gas)

I0 = UV light intensity of sample without ozone (reference gas)

The sample is drawn into the instrument through the sample bulkhead and is split into two gas streams. One gas stream flows through an ozone scrubber to become the reference gas (I0). The reference gas then flows to the reference solenoid valve. The sample gas (I) flows directly to the sample solenoid valve. The solenoid valves alternate the reference and sample gas streams between cells A and B every 10 seconds. When cell A contains reference gas, cell B contains sample gas and vice versa.

The UV light intensities of each cell are measured by detectors A and B. When the solenoid valves switch the reference and sample gas streams to opposite cells, the light intensities are ignored for several seconds to allow the cells to be flushed. The instrument calculates the ozone concentration for each cell and outputs the average concentration to both the front panel display and the analog outputs.

The instrument is operated as part of Defra’s Automatic Urban and Rural Network (AURN) and is serviced and calibrated by Ricardo Energy & Environment..

The hourly data from this instrument is available here

The last 24 hours of data can be viewed here