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March 1, 2017 at 10:36 am #1856
Wellntel utilizes next generation acoustic measurement technology, remote telemetry, and a cloud platform, to collect accurate, consistent, and reliable groundwater-level measurements from a wide range of production and monitoring wells and performs favorably compared to other instruments such as pressure transducers or tapes.
Groundwater levels measured by a USGS Pressure Transducer and a Wellntel sensor collected from a monitoring well during an aquifer pumping test in Wisconsin, September 2015. Wellntel data deviation from pressure transducer data was within 0.25% for the 20+ day test.
The Wellntel sensor measures signal time-of-travel and air temperature in the well, and the Wellntel cloud uses these measurements, along with historical and observed factors, to compute distance, or depth-to-water (D2W).
As an acoustic sensor, precision is driven by small computer rounding errors, the sensor sensitivity, or sample rate, and how well air temperature is known.
With in-well air temperature properly characterized, the precision of the Wellntel system is better than +/- 0.25% within the operational depth measurement range: 10 – 1600 ft.
Wellntel sensor sample level precision as percent of depth to water on a logarithmic depth scale.
Accuracy is an outcome of installation and operation
1) Initial setup
While the sensor is designed to be installed by a handy do-it-yourselfer using common tools, installation methods directly impact accuracy. It is important to “zero” the groundwater level to a “Measuring Point” (MP), the location, or datum, that will be used as the continual point of reference for all readings, whether local, or in a network.
When an owner or sponsor registers their Wellntel system, they are asked to measure and record the Sensor Elevation above ground surface, measured to the bottom of the sensor (not the probe wire, but the location of the threads where the sensor mounts to the cap.) An installation checklist is attached.
In the Cloud, this Sensor Elevation value is subtracted from the distance to water measurements taken by the system, in order to compute the depth-to-water below the ground level that is reported.
In an application with multiple measuring devices, consistent variation in values between devices can typically be traced to non-zeroed MPs. Cloud storage allows for historic data from Wellntel systems to be corrected retroactively if such a misunderstanding is found.
2) Basic sensor operation
The Wellntel Sensor sends sound energy containing non-random programmable sequenced data into the well. The information is created digitally and converted to a distinctive analog signal delivered via a signal generator positioned either in the well or above the well cap on a port that provides a signal path. Subsequent signal response is analyzed through a proprietary digital processing and statistical analysis method at the Sensor. This is, however, only an initial step toward a final reading result. The sensor alone doesn’t have all information required to calculate depth, so it bundles and transmits raw data to the cloud for vital compensation and auditing steps.
3) The Cloud: data gatekeeper and auditor
After a system is registered and installed, remote, cloud-based calibration of sensor settings and signal characteristics is completed by the Wellntel technical staff to improve performance. Calibration can often be completed within hours of installation, but, depending on environmental factors, may take a week or more. Once calibrated, the system will only require recalibration if there are dramatic changes in environmental factors, like changes to the well, housing, or background conditions.
It is possible that the Wellntel technical team will find during the calibration process, evidence of mechanical or environmental conditions that may limit performance or accuracy. In this case, a Wellntel representative will contact and work with the owner or sponsor to make local adjustments to improve the installation. Changes, if needed, are usually simple and inexpensive (even free), but may require similar time and tools as initial sensor installation. Our goal is to minimize this effort while ensuring best prospects for the data for the life of the system.
Once calibrated, the sensor will settle into regular operation. With each Wellntel sensor reading, a list of raw sample values, representing signal time-of-travel, are statistically ranked and sent to the Wellntel Cloud. Using history, signal characteristics, and other auditable factors as guides, the Cloud sorts through these data and accurately identifies the water level value which is then promoted to online hydrographs made available through Wellntel websites. This work is completed, usually, within 10 seconds of when the reading is taken.
Errors are possible and the system learns from them. Data anomalies caused by pump noise, well-design, and improper mounting can result in inaccurate depth values sometimes reaching online hydrographs. If one of these erroneous values appears, it can be flagged by an owner or sponsor and demoted, lifting the actual water level value from the raw data, if and when it is available.
4) Temperature matters:
With Wellntel, accurate air temperature characterization provides accurate data. The Wellntel sensor measures temperature at the sensor probe each time it takes a reading, and includes the measured temperature as part of its message to the Cloud. Wellntel measures temperature with a thermistor that has a resolution of 0.1 degrees C, and a precision of +/- 1%.
Groundwater temperature is an important part of characterizing air temperature in a well because it establishes the air temperature at a point just above the water surface. The Wellntel Cloud combines regional groundwater temperature observations with its own measurements to create an air temperature profile for each reading. This temperature curve is used to calculate the speed of sound in the well which is then used to calculate the water level from the preferred time value. Since regional groundwater temperature observations may not necessarily provide adequate resolution or precision, Wellntel solicits customers and partners to take and report their own groundwater temperature observations a few times a year, improving system accuracy.
* Local readings collected using the SensorLink “Take a Reading” function do not account for complete temperature characteristics, and will differ from both values presented in the Cloud, and values from other instruments. Local readings should be used for “in-the-range” comparisons only. It is important to complete (allow the transfer of data and the application of cloud compensations) and refer to cloud output groundwater levels to arrive at the most accurate information possible.
Additional information about the Wellntel Groundwater Information System can be found on the Wellntel Forum: https://www.wellntel.com/blog/forums/forum/new-to-wellntel/
Learn even more about Wellntel by listening in and asking questions during one of our online webinars hosted by Wellntel scientists and technicians: https://www.wellntel.com/webinars/
Mechanical Integrity and Installation
- Inspect the sounder probe for any signs of damage or abrasion. If either are seen, contact Wellntel to arrange for return of the unit for replacement.
- Take the time to straighten the sensor probe wire (using a firm grip, but without pulling the cord). Modest “bowing” in the wire will straighten with temperature and time, but there should be no kinks or twists.
- If the Wellntel sensor will be placed where a well “vent” once was, take care to ensure proper ventilation either by adding the included Wellntel vent, or by adding proper ventilation to an alternative well access port. Do not install a vent between the Wellntel sensor and a well cap or seal unless it is the one provided by Wellntel as other vents may allow the sensor signal to escape before entering the well.
- If the Wellntel sensor will be installed on an access port of a ventilated cap, use the Wellntel supplied, brass nipple to mount the sensor.
- Visually inspect the access port on the well cap or seal, checking for a clean and clear signal path into the well, removing dirt or grime and moving obstructions, like expanded gaskets, out of the way. It should be possible to easily insert the sensor probe through access port into the well without touching threads or walls. As it is inserted, feel that the probe is dropping cleanly into the space. If, as the sensor is twisted onto the vent or nipple, you feel resistance inside the well, stop and restart the process.
- Using the included diagram as a guide, use a tape measure to measure the distance between the bottom of the sensor (not the probe wire, but the location of the threads where the sensor mounts to the cap) and the ground surface. Make note of the distance.
- If the sensor is part of a network, and/or will be compared to other instruments, measure from the bottom of the sensor to the required measurement point used for the network and/or by other instruments. This distance will used to “zero” measurements ensuring water levels are measured accurately across the network and between instruments.
Server Settings and Calibration
- Register the sensor online at my.wellntel.com, and, as part of the registration process on the “Well Details” page, enter the measured height above ground, or the height above the required measurement point. This is the location used as the datum (zero level) for groundwater levels displayed on hydrographs and provided as output data ensuring accuracy across networks and between instruments.
- If groundwater level is known, enter the distance to water from the required measurement point on the Well Details page. If groundwater temperature is known. Both are optional but if provided, may assist remote calibration and improve accuracy.
- Following the Getting Started Guide, power the gateway and connect it to the internet. Then power the sensor and wait at least one minute for the sensor to complete its boot-up. Take several initial forced readings. These first few readings assist in remote calibration.
- Once the sensor is installed and readings begin to flow to the Cloud, the remote calibration period begins. Remote calibration can take hours, days, or weeks depending on the specific well and installation characteristics. It is important to visit my.wellntel.com from time-to-time in the first few days and weeks of operation. You can monitor calibration progress, but if information on your dashboard looks inconsistent or illogical or varies from your expectations, please contact firstname.lastname@example.org with questions or details of your concern.
Download this Wellntel Accuracy Fact Sheet 12-13-2017.
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