General Characteristics

The VOC/THC portable analyzer, Model 9388 incorporates two removable memory cards, the first is used to define the program cycles for the change of analytic conditions according to the characteristics of the chromatographic column for the analysis of specific hydrocarbons, the second memory card is dedicated to data acquisition which will later be downloaded to a PC for its management in a laboratory.

The versatility of the device permits the measurement of VOC/THC in emissions as well as specific hydrocarbons during direct sampling in chimneys or conducts or through a heated line, up to 40 metres. The detector is a Carbon atom counter.

The sample is introduced into a micro flame feeder through hydrogen and air, where any electric changes caused by the oxidation of CH4 to CO are proportional to the content of hydrocarbons in the sample.

The concentration is calculated through a calibration with a reference gas mixture. The electric changes are detected by two polarized electrodes and converted to electric signals by an electronic circuit.

Description

Model 9388 has been designed for the measurement of hydrocarbons which are reactive in ambient air and/or in emissions, removing the methane fraction from the total hydrocarbon concentration. Since catalytic separation is not always efficient, the separation technique is based on chromatography.

A sampling pump at the end of the pneumatic circuit fills a calibrated capillary circuit with approximately 0.6ml, the volume is normalized with the atmospheric pressure in order to obtain highly reproducible samples. This sample volume is injected into the chromatographic column through a rotating 10 way valve. The column is filled with PQS or another substrate which permits the separation of the methane fraction from the total hydrocarbon content.

The separated CH4 fraction is sent to the FID detector and the response is memorized in the internal microprocessor. In the preparation phase of the 10 way rotating valve a second sample is introduced subsequently into the FID detector in order to measure the total hydrocarbon content (THC). The electronic response is also stored in memory.

Subtracting the signal obtained from the methane fraction from the signal obtained from the total hydrocarbon, it is possible to obtain the value of the methane fraction in the total hydrocarbon content.

The device carries out an auto-zero before each measurement cycle, guaranteeing a great stability in zero drift. The three electronic signals are visible in the screen and are available as analogue outputs. An Intel 80C195 microprocessor controls all the functions related to analytic sequences as well as data management.

The diagnostic software package also controls:

• The operating parameters, alerts and states.
• Pre conditioning phases of the device.
• The automatic flame ignition system.
• Automatic alert generation in case of flame extinction or H2 leaks.

The alphanumeric screen with 4 lines of 80 characters presents the three values measured in ppm and/or in mg/m3 as well as any kind of occasional equipment failure. Via the firmware stored in the EEPROM, located in the in the card inserted in the front panel, the device can be easily configured for specific hydrocarbons such as Benzene, Toluene, Styrene, etc, up to a maximum of six species. The possibility of changing the program card and chromatographic column, make Model 9388 the best solution for the measurement of any type of hydrocarbon.

The measurement data and operational status are stored in the other 64K memory card. The data in this card can be downloaded to a PC, allowing the storage and management of data.