The Electronic Diffusion Tube is a device for measure gases that effect air quality.
What does EDT stand for?
EDT stands for Electronic Diffusion Tube. This robust device contains a sensor which records air quality data by measuring polluting gas concentration with an electrochemical gas sensor.
What batteries are used and where can I get them?
The EDT is fitted with long life non-rechargeable batteries. The EDT uses two lithium thionyl chloride (Li-SOCI2 14500) size AA non-rechargeable batteries, rated at 3.6VDC with nominal 2.0Ah capacity. These batteries can be purchased online from many suppliers including Saft, Tadiran, EEMB, and EVE.
Are the lithium Batteries safe?
Certain types of lithium batteries are a known fire hazard: if the batteries have low internal resistance and can discharge rapidly, this will cause overheating of the battery and rapid temperature rise, leading to a fire hazard. With lithium batteries the internal fault is normally short circuiting between the cathode and anode, but Lithium thionyl chloride batteries have a higher internal resistance and are considered one of the safest lithium batteries. Tests in the EDT show that a shorted battery will heat the EDT by only 5°C to 7°C, not enough to pose a fire hazard when in the EDT. Store the EDT with batteries below 30°C.
How do I change batteries?
To replace the two batteries that power the EDT:
1. Remove the EDT from the clip in the mounting bracket.
2. Unscrew the two halves of the EDT case to reveal the inner module of the EDT, consisting of the main Primary Circuit Board (PCB), sensor PCB and batteries.
3. The two batteries are located on the reverse side of the main PCB and are held in place with standard AA battery terminals. Remove the exhausted batteries and dispose of them, following local regulations for correct disposal of lithium batteries.
4. Insert new batteries, observing the correct polarity as displayed in the battery compartment.
5. Fit the inner module back into the outer case and check that the location key is correctly aligned. Screw together the two parts of the outer case, taking care to not over-stress the outer case thread. Check that the ‘O’ rings are seated properly and have not become dislodged and replace the silica gel package if it has fallen out.
6. Logging will be switched OFF and the time and date will not be set. As soon as the App is connected with the EDT, the EDT will automatically switch to Logging ON and the time (UTC) and date will be reset.
How long will the batteries last?
Battery life is largely affected by the energy required for Bluetooth broadcasting and EDT functions including erasing EDT data or regular downloads from the device will also reduce battery life. The table below gives typical battery life for different usage profiles.
Download frequency Logging interval Battery life
Weekly 30 seconds 8 months
Weekly 15 minutes 8-9 months
Monthly 1 minute 9 months
Monthly 15 minutes 10 months
What do I do if the silica gel sachet falls out?
The inclusion of silica gel sachets is good practice to reduce the chance of condensation around the electronics: it will absorb any extra moisture trapped inside the EDT. If the silica gel sachet falls out then place it back in the compartment next to the batteries.
If you lose the silica gel sachet then the EDT will still operate effectively. However, when opening the EDT to change batteries, take are not to expose the inside circuitry to high humidity. Always replace batteries in a dry environment.
Is the EDT waterproof?
No, the EDT is not waterproof. The EDT has been tested to IP56, but do not immerse. The EDT casing is designed to IP68 but the PTFE membranes must allow water vapour and gas access, so these woven membranes limit the IP rating.
Is the EDT weatherproof and can I leave it outside?
The EDT is not weatherproof but can be used outside in conjunction with the supplied external housing. The EDT can be mounted on a pole or a wall, using the external housing. This provides a clean look and protection for the device from the elements.
The EDT should always be fitted with the dust filter facing downwards in the external housing and the external housing cover should be closed with the pinch screws tightened using the 4mm hex key provided. There is also an additional hole for security tags to avoid tampering and theft.
The EDT is ideally mounted 2 to 3 meters from the ground and away from direct sunlight.
The external housing is designed to accommodate the “TamTorque” system widely used in industry. The two machined recesses allow the “TamTorque” strap to sit flush to the back plate while the outer protective shield is down. Alternatively cable ties can be used to secure to a post.
How much data can my EDT hold?
The EDT can hold over 500,000 records. The number of records created depends on the log interval chosen and the length of time that the EDT is logging. The table below shows some file size examples for different logging sessions:
Logging Period Log interval No. of Records
1 day 5 seconds 17,280
1 day 5 minutes 288
1 week 30 seconds 20,160
1 week 5 minutes 2,016
1 month 30 seconds 87,264
1 month 15 minutes 32,724
3 months 30 seconds 262,080
3 months 15 minutes 9,828
Data from the EDT can be deleted at any time. Please ensure that you have uploaded your data to AQGateway.com before using the delete function as deleted data cannot be recovered
How do I know if I'm running out of space on my EDT?
The EDT can hold over 500,000 records.
When connected to an EDT, the AQGateway App shows the amount of record blocks currently on the EDT.
Each record block represents approximately 70 records. When the number of record blocks reaches approximately 7,000, the EDT is nearing capacity.
If capacity is reached, the EDT will stop logging
How can I erase data from my EDT?
Since the memory holds over 500,000 records, you need not erase EDT memory after each download to the App. The EDT bookmarks the end of the last session and after your new session, it will only download that latest session.
Eventually you will fill up the EDT memory and it will stop logging when full. You can erase the EDT memory by connecting to the EDT selecting settings and then choosing the [Erase the EDT Data] option on the App.
It is good practice to erase the EDT memory after successfully downloading a very large session or before starting a long data log session to ensure you have adequate free memory in the EDT.
The Erase function should take a number of seconds as the whole memory is erased, irrespective of how much of it is used at the time of the erase. If the Erase seems to be very quick - 1 or 2 seconds - the erase may not have worked correctly. Battery levels need to be over 3.5V for the erase to work as it is a power heavy function.
NB - The Erase function is a power intensive function - to ensure the erase works correctly, ensure that battery voltage is at 3.5V or above
What sensors are installed in the EDT?
The EDT accepts one of any seven gas sensors from Alphasense. The gas sensor installed is specified on the label on the side of the EDT. The EDT can be fitted with any of the following sensors :-
CO, H2S ,NH3, NO, NO2, OX, SO2
Data sheets specifying sensor performance can be found on the Alphasense website: www.alphasense.com in the Alphasense Air section.
How do I start and stop logging?
Once the EDT has started logging, it will log continuously.
The only circumstance in which logging does not continue automatically is if batteries have been removed and reinserted / changed.
The EDT will cease to log until such time as the EDT is connected to the App. Once connected, the EDT will log at the interval specified on the app.
How long will the batteries last?
The EDT is fitted with two lithium batteries. Some functions are very power hungry. The erase function is particularly power hungry and in order to run successfully, the batteries must have 3.5V or higher remaining.
Similarly, downloading data from the EDT, particularly if downloading a large volume of data, is power intensive.
As a general rule, once you see a deterioration in battery voltage, consider changing batteries to ensure the continued functioning of your EDT.
What happens if I open the EDT?
Opening the EDT exposes the inside circuitry and could potentially damage the circuit board - eg. if opened in high humidity. Unless changing batteries, please do not open the EDT.
My EDT is fitted with an NO sensor. What other gases can be measured using the EDT?
The EDT accepts one of any seven sensors from Alphasense measuring CO, H2S, NH3, NO, NO2, OX and
SO2 . Data sheets specifying sensor performance can be found on the Alphasense website: www.alphasense.com. Go to the Alphasense Air section
Where should I position the EDT?
It is best to put the EDT at a height that reflects the environment and so that the data collected reflects the air quality environment. Examples
Schools : - it is best to mount at about 1m to 1.5m height in schools, the approximate same level as students’ breathing.
Offices: it should be at sitting height
Warehouses : place an EDT at the loading docks, another in the offices and a third in the storage bays.
The EDT works in both indoor and outdoor environments but should be positioned within its external housing. Avoid positioning near doors and in direct sunlight. Try to place the EDT near the most activity so it is sampling the average environment.