We have tried to cover some of the most common questions here but please contact us if your question is not answered here.
1 minute video demonstrating how to install AQMesh pods (using post clips)
90 second video demonstrating how to install AQMesh pods (using steel banding)
Full length 10 minute video demonstrating how to install AQMesh pods (with narration)
In order for AQMesh to provide the greatest degree of accuracy, it is advised to co-locate the pod with a reference station. This will provide the information necessary for calculating our scaling variables; offset and slope. Scaling provides an increased level of accuracy, based on the local environmental conditions and how the sensors used react to that environment.
Scaling values are calculated over a specific time period and as such are based on the environmental conditions on site over this period. By applying these values for offset and slope we are able to determine the best possible performance results for this pod over the same period, and improve accuracy of the pod moving forward.
Scaling of AQMesh sensors is only required in certain circumstances:
• Following a sensor change, the new sensor will need scaling to its new environment
• Following a large step change in environmental conditions at the site, e.g. a change in average temperature of 10 degrees Celsius or more, compared to when it was scaled
In order to apply scaling to an AQMesh pod the user must first select to use advanced settings so that “PreScaled” values for each sensor are available for the downloaded period.
Regression comparison AQMesh PreScaled data versus reference or Gold Pod Scaled data, using the candidate pod on the x axis and the reference on the y axis. Regression analysis can be completed using Microsoft Excel, MathCad or similar mathematical programs.
Removal of potential erroneous data points and find Cartesian equation for line of linear trend line
Apply Offset and slope to full PreScaled data set (including erroneous data points)
Reference ≈ (PreScaled data x Gradient) + Y-Intercept
Gradient = Slope
Y-Intercept = Offset
AQMesh Scaled data = (PreScaled data x Slope) + Offset
Upload slope and offset values to the online application for each gas sensor and particle fraction.
Validate pod accuracy by following the scaling process by either; a second co-location with reference or co-location with Gold pod at the target location, at an interval determined by the users own QAQC process.
For long projects it is advised that data is validated every six months to account for any changes in calibration at the reference station.
For shorter projects, good practice for validation of data would be to run a scaling exercise both pre and post the trial period, providing full confidence in the data received from the trial.
AQMesh pods can also be scaled with diffusion tubes. For more information, read here.
Typical issues which can cause data from AQMesh to not look as expected when comparing it to reference are as follows:
- Phase shift
- This can be a large difference due to time zone differences, or small due to drift from internal clocks on reference instruments
- Units of measurement
- AQMesh reports data as standard as ppb for gases and ug/m3 for particle mass
- While every effort to compensate AQMesh for interfering gases, temperature, humidity and other environmental effects via the algorithm is done, some variation from reference, especially in the low ppb values, is possible
- If AQMesh pods are in direct sunlight for extended periods of time, this may make a slight difference to readings
- Reference instruments can also suffer from interferences and careful review of the instrument manual should be completed
- Sensor change
- When a sensor has been changed, the sensor requires a 2 day stabilisation period and 2 day rebasing period, during which data from that channel (and any related by cross gas effects) will not be valid. The invalid data will be flagged on your data file.
If you cannot see the cause of why your AQMesh data does not look correct, please refer to your local distributor, or contact us.
We apologise for the inconvenience caused by a sensor failure. Environmental Instruments Ltd (manufacturers of AQMesh) provide a 12 month warranty for all electrochemical sensors when used correctly. Within this 12 month period, a replacement sensor will be sent out within 24 hours of our receipt of sensor diagnostics informing us of the failure.
The sensor then needs to be changed and returned to us – we will then investigate the cause of the failure. AQMesh, together with the sensor manufacturers, are working to improve the sensor failure rate which is currently less than 1% on average per month, however we do see a peak during winter months.
This video will demonstrate how to change a sensor in an AQMesh pod:
For more information please contact us.
The default power option for AQMesh is a DC power supply which can be connect to local mains power or a solar panel. Some pods, however, use a lithium battery, and AQMesh can also be used with a rechargeable NiMH (Nickel Metal Hydride) battery pack. This has a much shorter battery life than the lithium battery, but is supplied via your local distributor as a pack of two batteries and a charging unit. These are the same size as the current lithium batteries (4 x 1 in shape) so can be used in pods which previously had the non-rechargeable lithium batteries.
How will I know if my lithium battery needs replacing?
A low battery alert is sent when a lithium battery has approximately a month's power remaining. This should allow plenty of time for a replacement to be sourced and installed without interrupting data. The lithium battery is not rechargeable and must be disposed of according to local regulations. As the power delivery is extremely stable across the battery's life it is not possible to measure remaining battery charge before the point that it declines after approximately 2 years.
This graph shows the typical lithium battery life pattern:
How to replace the lithium battery in an AQMesh pod:
For more information please contact us.
To set up an effective trial to compare AQMesh performance against a reference station we recommend following this advice:
- A reliable reference station (maintained and ideally certified) should be chosen as the trial location, in an environment where there is some pollution
- At least 2 AQMesh pods should be used to allow comparison between pods, as well as against reference
- The essential parameters measured by the reference station: NO, NO2, O3, RH and temperature
- Optional parameters measured by the reference station could be: SO2, CO
- All trial pods should be co-located with the reference station inlet, ideally immediately adjacent or at least no more than 1m apart, like shown:
- Pods must be allowed 2 days for environmental stabilisation*
- Readings will reach optimum performance after an additional 2 days when rebasing is completed
- If pods are moved at any point, environmental stabilisation* and rebasing will need to be initiated again
*Environmental stabilisation is the process by which electrochemical sensors adjust to a change in ambient temperature or relative humidity. Any significant change to these conditions will affect readings until the sensors have stabilised.
Examples of changes in environmental conditions:
- Transportation in an enclosed environment, eg: a car, van or plane where the internal environment is controlled with heating or air conditioning
- When a pod is brought into an office environment, even briefly, for storage or maintenance
Examples where environmental conditions are maintained:
- Transportation of pods by foot from one location to another
- Transportation of pods in an open truck
If your comparison data still doesn't look right, please see the 'Why doesn't my data look right?' FAQ to identify common issues.
For more information please contact us.
In order to calibrate/validate AQMesh (in a similar way that reference equipment needs checking on a 6 monthly basis), it is recommended to set up a "gold pod", whereby one of your pods goes through a co-location and scaling exercise to then be used as a data validation instrument within your network of pods:
Complete a co-location and scaling exercise with a pod to validate it against reference and create your gold pod.
Co-locate your gold pod with a locally deployed pod to validate its readings.
Move the gold pod around the network to continue validating each pod.
Once network validation has taken place, return the pod back to reference to go through the process again.
If you need further information on creating gold pods please contact us.
If your pod doesn't seem to be connecting to the server, please go to the pod and check the LED status before contacting us and we can then diagnose the problem.
Note1: A local issue can be:
- The modem cannot attach to the network (usually due to bad GPRS coverage)
- The modem cannot connect to the APN (usually due to bad GPRS coverage or to wrong settings)
- Unexpected error (other than above)
Note2 : An issue with the server can be:
- Cannot connect to the server (offline or wrong settings)
- Response timeout (the server did not reply in time to a command)
- Response error (some data have been received from the server, but the format of the response is not correct)
In these instances, please contact us for further advice on rectifying the issue.
Users are able to use their own SIM card, however by not using the global SIM supplied with AQMesh we will not be able to provide the same level of support for any transmission problems. The global SIM card provided with your AQMesh pod is capable of searching all local providers to find the strongest signal available at all times and is the recommended option.
If you would like any more information about this then please contact us.