Percometer
An instrument for the test hole.
An ultrasonic water-level logger that sits on a pipe in the test hole and records the drop on a fixed schedule. The design is complete and its firmware is written; the first prototype is next.
- Status
- In development
- Design as of
- 2026-10-03
Percometer
Design model · not a photograph
The model is the Percometer design itself — the Fusion 360 housing, the KiCad circuit board and the module envelopes — not a rendering made for this page.
In the field
Set it, place it, leave it.
The device takes over the part of the test that is pure waiting and watching. The person running the test still prepares the hole and decides when the test is sound.
- 01
Set the test
Choose the lot, the reading interval and the test length on the device. The screen shows the label the next test will get — 12A, 12B, and so on — and remembers the last settings.
- 02
Place it
Stand the 3 in. pipe on the bottom of the hole and seat the device on top. The sensor face is then a fixed 25 in. above the hole bottom.
- 03
Start
Press SELECT on START. A 10-second baseline is taken first, then the timed readings begin.
- 04
Leave it running
At every interval the device averages up to 20 pings and stores the result. Topping up the hole is normal: a rise of 0.5 in. or more is logged and flagged, and later rates are measured from the new level.
- 05
Finish
When the last reading is verified in memory the device shows COMPLETE and the slowest interval of the test, as a field check. Final rates are worked out in the office.
Representative screens from the Percometer's menus. Layout may change before production.
How a reading is made
Distance to the water, corrected for the air in the pipe.
The sensor face sits a fixed 25 in. above the bottom of the hole, so the water left is simply 25 in. minus the reading. Watch a simulated test:
| Time | Depth | Drop | Rate |
|---|---|---|---|
| 10:05 | 15.25" | ||
| 10:15 | 16.50" | 1.25" | 8.00 |
| 10:25 | 17.65" | 1.15" | 8.70 |
| 10:35 | 18.70" | 1.05" | 9.52 |
| 10:45 | 19.70" | 1.00" | 10.00 |
| 10:55 | 20.65" | 0.95" | 10.53slowest |
| 11:05 | 21.40" | 0.75" | 13.33not counted |
Final rate 10.53 min/in → DPH class 10.1–20.0. The last interval had 2.60 in. of water left — inside the bottom 3 in. — so it does not count.
Measured from a fixed point
The two-head ultrasonic sensor looks down the pipe to the water. Because the pipe stands on the hole bottom, the water left is simply 25 in. minus the reading — no hole depth needed.
Temperature-corrected
A probe measures the air in the pipe and the speed of sound is corrected for it (c = 331.3 + 0.606·T m/s). If the probe fails, the last good value is used and the reading is flagged.
One reading, many pings
Each reading uses up to 20 pings in a 10-second window. Outliers are rejected (median / MAD) and at least 10 must agree, or the reading is saved as missing.
Never a fake number
A rate that cannot be measured is left blank, never zero. Missing readings, top-ups and interrupted tests are flagged in the record, not smoothed over.
Controls and interface
Three buttons, one screen, nothing to pair.
Everything is done from the lid: a small display, three buttons — UP, DOWN and SELECT — and a power switch. There is no phone app and no connection to set up in the field.
| UP / DOWN | Move between rows; while editing, change the value (hold to run it). |
|---|---|
| SELECT | Edit a value, finish editing, or start the test from START. |
| Hold SELECT 1.5 s | During a test: ask to stop, then confirm. |
| Hold UP + DOWN 5 s | While idle: ask to erase all records. Defaults to No; expires after 30 s. |
Connection to the software
Plug in once. Nothing is erased until it is safe.
A USB cable connects the device to Percolation Manager. The software reads every stored test, saves the read to a file, reads that file back and compares it. Only then can the device be erased — and the device itself still asks for confirmation.
- 1ReadEvery stored test, over USB
- 2SaveThe read is written to a CSV file
- 3VerifyThe file is read back and matched
- 4UnlockErase becomes available
- 5ConfirmOn the device: defaults to No
Specifications
What the design says — and how it is known.
Every value is marked with where it comes from. Nothing here has been measured on a built unit yet.
- Design value
- Taken from the Percometer's housing, circuit or firmware design.
- Calculated
- Worked out from the design, not measured.
- Provisional
- Set in firmware; to be confirmed by bench testing.
- To be measured
- No figure until a prototype has been tested.
| Sensing method | Two-head ultrasonic sensor looking down the pipe at the water surface | Design value |
|---|---|---|
| Mounting | Sits on a 3 in. pipe standing on the bottom of the hole; sensor face 25 in. above the hole bottom | Design value |
| Each reading | Up to 20 pings over a 10 s window, outliers rejected (median / MAD), at least 10 accepted | Design value |
| Temperature correction | Air temperature in the pipe; speed of sound c = 331.3 + 0.606·T m/s | Design value |
| Accepted distance range | 100 – 4,000 mm | Provisional |
| Accuracy | Not yet measured — bench and field testing planned | To be measured |
| Reading interval | 1 – 60 min | Design value |
|---|---|---|
| Test duration | 1 – 720 min | Design value |
| Defaults | Every 5 min for 60 min — 13 readings including the start | Design value |
| Labels | Lot 1 – 999; tests on a lot are labelled 12A, 12B … 12Z | Design value |
| Storage | 32 KB non-volatile memory, append-only, checksum on every page | Design value |
|---|---|---|
| Capacity | 34 one-hour tests at the default settings | Calculated |
| Flags kept with each reading | Water rose (top-up), missing reading, temperature fallback, interrupted test | Design value |
| Transfer | USB cable to Percolation Manager; erase needs confirmation on the device | Design value |
| Controller | Raspberry Pi Pico 2 W (RP2350) | Design value |
|---|---|---|
| Display and controls | 0.96 in. OLED, three buttons, power switch, status LED, beeper | Design value |
| Power | Single-cell lithium-polymer pack, charged over USB-C with the lid off | Design value |
| Battery life | Not yet measured | To be measured |
| Housing | Printed ASA, Ø115 mm × 151 mm overall (to the top of the power switch), TPU splash gasket under the lid | Design value |
From the Percometer design files as of 2026-10-03. Subject to change before production.
Development path
From design to a device you can rely on.
- DesignCircuit, housing and firmware designed together
- Design checksClean electrical and design-rule checks; housing fit checked in software
- Firmware tests7,827 automated checks on simulated sensors and memory
- 4PrototypeFirst boards and printed housing built
- 5Bench testingReadings in a pipe against a reference
- 6Field validationSide-by-side tests in real holes
- 7ProductionUnits for order requests
See development status for the detail behind each step.
Next step
Be one of the first to use it.
Order requests for the Percometer are open now and are answered by email with availability and lead time. Offices that want to help validate the prototype in the field can join the pilot.