A vented pressure transducer has a small tube in its cable that carries outside air to the back of the sensor, so it measures water depth directly. An absolute (non-vented) transducer has no tube and reads water plus atmosphere, so you must subtract a separate barometric record. For a monitoring well or stream stage that is read every few months, absolute loggers with a Barologger are the usual choice. For a short pump test, a tank or any job where you want the depth in the reading, vented is simpler. ERE carries both from Solinst and Heron, and this guide shows how to pick between them.
In this guide
- What is the difference between a vented and an absolute pressure transducer?
- How much error does barometric pressure add?
- Which vented transducers does ERE carry?
- Which absolute loggers pair with a Barologger?
- What range and accuracy should you choose?
- What should you check on a vented cable?
- When do you need a live signal instead of a logger?
- How do you choose, step by step?
- Frequently Asked Questions
What Is the Difference Between a Vented and an Absolute Pressure Transducer?
A vented (also called gauged) transducer measures pressure relative to the air above the water; an absolute transducer measures pressure relative to a vacuum. A submersible transducer senses the weight of the water above it. The air above the water also presses down, and that pressure reaches the sensor too.
- Vented: a vent tube runs the length of the cable from the surface to the sensor, so air pressure acts on both sides of the diaphragm and cancels. The reading is water depth.
- Absolute: the logger is sealed, with no cable to the surface. It records water plus air pressure, and software subtracts a barometric record afterwards.
A transducer is only the sensor. A logger adds memory and a battery, and a transmitter adds a standard 4-20 mA output. The same vented-versus-absolute choice applies to all three. The U.S. Geological Survey manual Use of Submersible Pressure Transducers in Water-Resources Investigations covers the pressure principles, planning, installation and common problems in detail.
How Much Error Does Barometric Pressure Add?
An uncompensated absolute logger turns every air-pressure change into an apparent water-level change. One kilopascal of pressure equals about 10.2 cm of fresh water, so a 2 kPa swing in air pressure, an illustrative figure for a passing weather system, reads as roughly 20 cm of water that is not there.
Compare that with the instrument error. The 5 m Solinst vented models list ±0.3 cm, so uncorrected barometric drift is dozens of times larger than the sensor's own error. That is why every absolute deployment needs a barometric record, and why vented models are sold on the claim that they do not.
The correction is not free of error either. The Solinst Barologger 6 lists ±0.05 kPa accuracy, which is about 0.5 cm of water. A compensated absolute record therefore carries the logger's error plus about half a centimetre from the barometer. The Barologger record covers loggers within 30 km and each 300 m of elevation change; beyond that you need a second one. Our guide What Is a Barologger? covers the procedure.
Which Vented Transducers Does ERE Carry?
ERE lists two vented families: the Solinst LevelVent 5 and AquaVent 5 for shallow work, and the Heron VENTED+ for deeper ranges. Figures below come from the product records.
| Model | Ranges listed | Accuracy listed | Memory | Notes from the record |
|---|---|---|---|---|
| Solinst Model 3250 LevelVent 5 | M5, M10, M20 (5, 10, 20 m) | ±0.3, ±0.5, ±1 cm | 150,000 logs | Up to 20 m submergence; built-in hydrophobic filters and desiccants, nothing to replace |
| Solinst Model 3500 AquaVent 5 | M5, M10, M20 | ±0.3, ±0.5, ±1 cm | 150,000 logs | SDI-12 and MODBUS options; user-replaceable AA lithium batteries in the wellhead |
| Heron dipperLog VENTED+ | 10 to 120 m (30 to 400 ft) | ±0.05% FS typical | 32,000 data sets | 316 stainless steel and Delrin body; sintered Teflon air filter in the wellhead; about 7-year battery at 5-minute readings |
The LevelVent 5 and AquaVent 5 connect to the wellhead through vented cable assemblies. Each cable carries power and communication wires plus the vent tube, in a polyurethane jacket, with a hydrophobic filter protecting the tube. Standard lengths run 5 to 100 ft, with custom lengths up to 500 ft. The two Solinst models differ mainly in connectivity: the AquaVent is the one to specify when the logger must feed an SDI-12 or MODBUS system.
Which Absolute Loggers Pair With a Barologger?
Absolute loggers suit sites where a long cable is awkward, where the logger hangs on a short wireline, or where one barometer can serve many wells. The records list these:
- Solinst Levelogger 6: Hastelloy pressure sensor, 0.05% FS accuracy, 150,000 readings and a 10-year battery in a 22 mm by 160 mm stainless body.
- Solinst Levelogger 6 Junior: the same sensor at 0.1% FS with 75,000 data points and a 5-year battery, for shorter projects.
- Heron dipperLog 128+: 316 stainless steel, ±0.05% FS typical, 128,000 readings and up to 15 years on its lithium battery.
Pair any of them with a Barologger 6 on site. Our water level data logger buyer's guide compares the full range, and the water level collection lists everything ERE stocks for groundwater levels.
What Range and Accuracy Should You Choose?
Choose the shortest range that covers the deepest water you expect, plus margin for a storm or pumping drawdown. Accuracy is quoted as a percentage of full scale, so the error grows with the range.
The Solinst figures show it: 0.05% of 5 m is 0.25 cm, listed as ±0.3 cm, while the 20 m model lists ±1 cm. The Heron VENTED+ lists ±0.05% FS typical across 10 to 120 m, which is 0.5 cm at 10 m but 6 cm at 120 m. A well with 8 m of water belongs on the 10 m range, not a 30 m one.
The Solinst vented models are listed for up to 20 m of submergence. Deeper water points to the Heron VENTED+, or to an absolute logger with a Barologger.
What Should You Check on a Vented Cable?
The vent tube is the part that can fail, so inspect it. It needs a clear path to the air, and the filter on the wellhead end is what keeps liquid water out of the tube.
- Cable length is fixed at order. Depth to water plus the submerged length sets it. The Solinst cables come in standard lengths, with custom lengths on request, so confirm depth before you quote.
- Filters and desiccant. The Solinst records list built-in hydrophobic filters and desiccants that need no replacement, and Heron lists a sintered Teflon filter in the wellhead that is not replaced. Spare dust caps, biofoul screens and a vented cable blowout fitting are listed as vented datalogger accessories.
- Kinks and crushing. A pinched cable can close the vent tube. Route it through the well cap as designed and avoid sharp bends.
- Wellhead fit. The LevelVent 5 deploys with a Solinst 2 in well cap assembly; ask us about 4 in casings.
The Heron VENTED+ record does not list its cable lengths. Ask us before you specify one.
When Do You Need a Live Signal Instead of a Logger?
If a controller, alarm or telemetry system must react to the level, you need a transmitter with a 4-20 mA or digital output, not a logger you download. Vented sensors are the usual choice there, because the reading goes straight to the PLC with no barometric correction step. See our 4-20 mA pressure transmitter buyer's guide for scaling and loop power, and water level telemetry for remote wells.
For manual spot checks in the same wells, a water level meter is the check on any logger's drift. The USGS manual Methods of Measuring Water Levels in Deep Wells describes the manual methods.
How Do You Choose a Vented or Absolute Transducer, Step by Step?
- Note the maximum depth of water. Add margin for drawdown and storms.
- Pick the shortest range that covers it. This keeps the full-scale error small.
- Decide how the data leaves the well. Download in the field, SDI-12 or MODBUS to a system, or 4-20 mA to a controller.
- Choose vented or absolute. Vented for depth in the reading and short setups; absolute with a Barologger for many wells or deeper water.
- Size the cable. Vented models need a cable cut to depth to water plus submergence.
- Add accessories. Well cap, spare caps and filters, and the right interface cable.
- Send the details. Quote by model, range and cable length and we confirm availability.
Need a vented or absolute water level logger?
Send us the well depth, expected water range and how you collect data, and we will confirm the model, cable length and accessories.
Frequently Asked Questions
What is a vented pressure transducer?
It is a submersible pressure sensor with a vent tube in its cable that carries outside air to the back of the sensor. Air pressure cancels, so the reading is water depth with no barometric correction.
Do vented pressure transducers need barometric compensation?
No. The Solinst LevelVent 5 and AquaVent 5 records list automatic compensation or no compensation required. Absolute loggers do need a barometric record, such as a Barologger.
Can a vented transducer be used in a sealed or closed tank?
Only if the vent tube is open to the same air pressure as the tank headspace. If the tank is pressurized differently from the surface, the vent reference is wrong and you need a different arrangement. Send us the tank details.
How deep can a vented transducer go?
The Solinst vented models are listed for up to 20 m of submergence. The Heron VENTED+ lists ranges from 10 to 120 m (30 to 400 ft).
Do you quote vented pressure transducers across Canada?
Yes. Send the model, range, cable length and quantity through the quote form and we confirm availability for delivery across Canada.
Related articles
- Water Level Data Loggers: Buyer's Guide for Canadian Groundwater Monitoring
- What Is a Barologger? Barometric Compensation Explained
- 4-20 mA Pressure Transmitter Buyer's Guide for Canada
- Solinst Levelogger 5 Groundwater Monitoring Guide
Lire en français : Transducteur de pression ventilé ou absolu : guide pour les eaux souterraines au Canada