Ion-science TVOC Bedienungsanleitung PDF herunterladen (Seite 6)

TVOC MANUAL Ion Science Ltd

Page 6 of 32

Unrivalled Detection. www.ionscience.com

Introduction to TVOC

TVOC is a fixed continuous monitor for the detection and measurement of total volatile organic compounds,

which can be dangerous from both a poisoning and explosive perspective. Total VOC’s are detected using

PID (Photo ionisation detection) technology.

TVOC has a number of user selectable features which define its operation and will be application dependent.

The user can define the detection ranges or 0.01 - 10ppm, 0.1 – 100 ppm or 1 – 1,000 ppm (Default);

detection units, either ppm or mg/m

; and the duty cycle time i.e. the frequency that the instrument takes a

measurement. Duty cycles are explained in more detail under TVOC set up, and Operation.

IMPORTANT: TVOC can be calibrated on alternative gases to Isobutylene however to ensure TVOC

remains within specification, the correct concentration for the alternative gas must be chosen.

Example: Benzene gas has a response factor of 0.5 which means only half as much concentration is

required to produce the equivalent to Isobutylene.

The ideal gas / concentrations used to set the calibration SPAN are shown below:-

Lower limit Upper limit

10 ppm range 8 ppm 12 ppm Isobutylene equivalent

100 ppm range 90 ppm 110 ppm Isobutylene equivalent

1,000 ppm range 90 ppm 110 ppm Isobutylene equivalent

How to calculate alternative concentration of gases for gases other than Isobutylene:-

Calibration Ideal response Response factor Ideal calibration gas

Gas for Isobutylene concentration

Benzene 100 x 0.5 = 50 ppm

Isoprene 100 x 0.7 = 70 ppm

Isobutylene 100 x 1.0 = 100 ppm

Carbon disulfide 100 x 1.4 = 140 ppm

Ethyl acrylate 100 x 2.0 = 200 ppm

For other gas response factors please refer to the Ion Science web site or contact Ion Science Ltd.

http://www.ionscience.com/GasSearch/tabid/87/Default.aspx

WARNING: Ignoring these guide lines may result in calibration failure, loss of resolution or loss of range.

The default settings of TVOC are:

Detection range – 1 – 1000 ppm

Units - ppm

Signal update - 60 seconds

TVOC gives a continuous 4-20 mA output which can be integrated into a DCS control system to give an

indication of VOC levels in the operating environment. Note the 4-20 mA output must be externally powered

with 8-35 V.

In addition to the 4-20 mA output TVOC has an LCD display showing gas concentration and 4 colour LED’s.

LED functions are as follows:

Green - is an indicator of TVOC’s working status

Red - is the fault indicator

Yellow x 2 - are calibration status indicators

Please see Calibration for more information on LED status.

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