The automatic weighing system AWS-1 consists of the following principal components:
- Dustproof weighing chamber with:
- Filter disc magazine for holding filters before and after weighing (20 magazine discs with 16 positions each, total capacity 320 filters)
- Carrier fork for transporting the filters within the system
- Microbalance (optional, most existing microbalances can be integrated after modification)
- Reference magazine for holding reference filters and reference weights
- Filter coding station (optional)
- Reading station for identifying coded filters (optional)
- Ionization fan (optional)
- Fan filter unit (FFU) to protect the weighing chamber against contamination
- Climate control unit (optional)
- Control panel for controlling system components manually
- PC with AWS Control system software (featuring custom encoding for all 47 mm filters)
- Power supply cabinet underneath the weighing chamber
- Side chamber for storing complete filter disc magazines
The AWS-1, being a modular system, is assembled with optional components according to the customer’s individual requirements. All optional components are integrated into the main system and are fully compatible with the system’s hardware and software. All components operate fully automatically within the system.
The coding station can be supplied as a separate unit on request in order to allow external filter coding.
Operating principle and weighing process
Before weighing takes place, the system settings and all the parameters for the forthcoming weighing job are entered in the PC using the AWS Control software. Next, the unladen sampling filters are placed in the filter disc magazine of the AWS-1 by hand. The filters are then preconditioned in the closed weighing chamber for a user-specified period of time, e.g. according to EN 12341 for 48 hours, at preselected temperature and humidity. If the filters are to be identifiable, their edges are punched with a code by the optional coding station.
The next step is the first weighing series, which consists of weighing the unladen filters, usually in two weighing passes. All the selected filters are thus consecutively weighed once and then for a second time. If discrepancies lying outside the specified tolerances are recorded between the first and second weighing passes, the relevant filters are weighed again in a third pass. The carrier fork automatically transports the filters between the system components (e.g. magazine → coding station → balance → magazine). The optional ionization fan neutralizes the filters (“eliminates” the static electricity) and thus enhances weighing accuracy.
Once the unladen filters have been weighed, they are placed in filter cartridges and installed in a dust sampler or other sampling system. Sampling then takes place according to EN 12341 – as a general rule, each filter is exposed to airborne dust for 24 hours.
After sampling, the filters are returned to the filter disc magazine and conditioned again. The second weighing series (weighing the laden filters) follows, once again with two or possibly three weighing passes. Previously coded filters are identified by the reading station, which allows the laden reading to be compared directly with the preceding unladen reading. Both before and during the weighing series, verification weighing operations are performed with reference filters in order to monitor the climatic conditions inside the weighing chamber. During the weighing operation, all the data (weight values, mean values, weight difference between unladen and laden filters, and ancillary data, such as temperature and relative humidity) are saved in the database on the system PC.
The saved data can subsequently be exported for analysis and processing. The concentration of suspended particulate matter is calculated from the weight difference between the laden and unladen filters, giving consideration to the air flow rate during the collection period.
The gravimetric assessment of particulate samples prescribed by European regulations has been performed in laboratories by way of manual weighing procedures in most cases thus far. Given that both unladen and dust-laden filters have to be weighed several times in order to obtain a mean value, numerous weighing operations are required. This monotonous, repetitive task places a considerable burden on laboratory technicians, and entails a relatively high risk of incorrect values being recorded during weighing and when the results are being transferred. The automated weighing operation performed by the AWS-1 in dustproof, controlled conditions substantially alleviates manual strain, prevents weighing errors and delivers reliable, precise results.
Detailed information is contained in the data sheet “Automatic Weighing System AWS-1”.
The information on this website represents the state of knowledge at the time of writing. Technical specifications are subject to modifications. Comde-Derenda GmbH accepts no liability whatsoever for the content provided or for damages resulting from the use of its products.