Microbiological air quality is a key parameter for controlling important environments. From food processing plants, laboratories up to operating theatres, in all cases the microbial load from air is critical for ensuring safe operation.
Air samples are devices designed in order to aspire specific air volumes and send particles over the agar surface of a petri plate containing specific culture media for micro-organisms.
The different levels of bacteria present in air samples led to different colony forming units (cfu) into microbial cultures, therefore the cfu counts can be correlated with air quality.
Professional air samples have different designs, however in most cases the underlying operating structure is the same. Professional instruments includes electronic controls for controlling flow, time, cycles and often can be programmed. For this reason the range prices are between 500-1500$ or more.
Herein is enclosed an instrument (Impactor sampler) able to obtain the same results with the design as simple as possible.
If you are interested in the theory and different approaches for air sampling you can review the next link:
Step 1: Printing Instrument Parts
The instruments is composed by 4 different structures. There is not special requirements for 3d printing, I printed my units with PLA in a conventional FDM 3D printer:
- Layer height, 0.2 mm
- Shell thickness, 0.4 mm
- Bottom/Top thickness, 0.4 mm
- Fill density, 20%
The instrument body is formed by three different parts plus one cover. Since the body parts will be assembled with Philips screws, probably a higher fill density can ensure the capability of screw-unscrew several times without compromising the body insertion.
Step 2: Bill of Materials
All the current materials has been purchased to Amazon.es,
- 3/8'' Nut
- Converter Screw adapter for tripod
- Camera Tripod, It can be used on elevated surfaces such as a bench-top or work table in other cases you may need larger tripods.
- DC1,8-15V 2A PWM speed controller
- Electrical wire
- Switch ON-OF 12v
- Variable rheostat / potentiometer 0-100 Control Dial Plate
- DC 5,5 millimeter x2,1 millimeter, female plug for panel
- 12V CC brushless turbine DC 75mmx75mmx30mm
- silicone gasket or equivalent , I found that gasket (5 x 4 x 6 in) from espresso coffee makers are perfect )
· 4 Drywall Black Phosphate Phillips Screws 4.2 x 70 mm
· 2 Round Head Phillips Self-drilling screws 2.5 x 40 mm
Step 3: Wiring
It's a very simple step
1) Fan: In most cases fans are sold with a Dupont connector. You must to cut it and strip the wires for connect to the speed control board
2) Switch & DC female. There's no special secret, you need to solder or use isolated Faston connectors
Step 4: Assembly
Enclosed is the Assembly.pdf guide, in this 9 slides you can easily follow the assembly process step by step.
Step 5: Electric Power Supply
This device has been designed and calibrated for working at 12v, at this stage you can chose between:
- Standard AC/DC 12v 1-1,5 A power supply, this is my option
- External 12v battery, if you need to take samples on the field or need freedom of movement.
in this case you'll also need a male-male 5.5DC wire
Step 6: Calibration
Using an standard anemometer ( Tacklife DA03, from Amazon) you can measure the air velocity and calculate the flow rate. With the current design it's linear between 40-95%.
Q = Av
Q = liquid flow rate (m3/s or L/s)
A = area of the pipe or channel (m2)
v = velocity of the liquid (m/s)
Step 7: Sampling
Depending of each environment or your quality standards, are necessary different sample sizes. In most cases, for clean environments the standard is 1m3 / 15 min.