Gas monitoring plays an important role in the storage of fruit and vegetables.
During the ripening process fruit and vegetables produce, beside CO2, organic volatile compounds such as ethylene, ethanol, acetaldehyde, acetone and ethyl acetate.
Amongst the most important “ripening” indicators are ethylene, ethanol and acetaldehyde. Monitoring of these gases enables the exact control of the ripening stages and thus an accurate regulation of the oxygen and carbon dioxide content of the storage atmosphere. This can result in a reduction in cost of gas blanketing plus the enhancement of the lifetime and quality of the perishable goods.
IGD Limited can offer a number of alternatives for gas monitoring.
Tocsin 103 Series Detectors
These offer a cost effective monitoring method under specific circumstances. When assessing the suitability of the 103 series detector consideration must be given to the temperature and humidity specification. This type of detector is an electrochemical detector, all ethanol detectors of this type will have cross sensitivity to CO. Therefore if CO is likely to be present, typically from diesel or gas powered fork lift trucks, misleading results could occur. If it is possible to utilise this detector type then they offer the advantage of cost and long stable calibration periods. The basic detector provides a linear 4-20mA industry standard output. Addressable types are available allowing networking of detectors onto data highways thus reducing costs and increasing accuracy by eliminating analogue I/O inaccuracies.
The Tocsin 102PID series detectors are based on Photo-ionisation technology and offer excellent discrimination for a number of gases including Ethanol. Unlike electrochemical detector types they have no cross sensitivity to other gases which could be present, in particular CO. They are also immune to contamination effects from acetaldehyde. The unit has a local display and provides a linear 4-20mA industry standard output. The units’ main disadvantage for applications monitoring a large number of points is cost and maintenance. A PID detector will require regular replacement of its UV light source.
Tocsin 700 Sampling Systems
If detectors cannot be placed directly into the area to be monitored due to climatic conditions (typical of cold stores) then a sampling system can be considered. These systems have the advantage of central monitoring using high accuracy IR detectors. Such systems draw a pumped sample from the points to be monitored, sequentially. If tube runs are extended then the time to purge can be long resulting in long cycle times.
With such systems there are pumps and filters to maintain resulting in a high cost of ownership. Sampling systems should only be considered if other alternatives are not possible.