TMS Datalogger
TMS dataloggers measure air temperature, soil temperature, and soil moisture in long-term field deployments. Each unit contains three temperature sensors and one soil moisture sensor, allowing microclimate measurements close to the ground surface.
A sealed lithium battery good for more than 10 years in Basic mode and a large internal memory (507 872 records, about 14 years at 15-minute intervals) let TMS loggers run fully autonomously with almost no maintenance, and when you do visit, a month of data at 15-minute intervals comes off the logger in under three seconds. Their robust construction and low cost make them well suited to long-term monitoring across large areas, even in harsh environments. More than 100 000 TOMST dataloggers are in use worldwide, some still logging after more than 14 years in the field.
A peer-reviewed description of TMS dataloggers has been published in Agricultural and Forest Meteorology. Read the article.
Technical specification (TMS Standard / base unit)
- Length
- 29 cm overall (10 cm buried tube)
- Weight
- 108 g
- Memory
- 507 872 records (about 14 years in Basic mode, one reading every 15 minutes)
- Battery
- Sealed lithium 2 600 mAh - more than 10 years in Basic mode, with the cell chemistry guaranteed for 10 years by the battery manufacturer. Units installed over 12 years ago, on older hardware, are still recording.
- Connector
- Touch probe for settings and data download to PC via TMD Adapter
- Software
- Data download and configuration using Lolly
- Temperature sensors
- 3 x MAXIM/DALLAS DS7505U+
- Resolution
- 0.0625 °C
- Accuracy
- ± 0.5 °C
- Measurement range
- -40 to +60 °C (can measure -60 to +85 °C; may reduce battery life)
- Moisture sensor
- 1 x soil moisture sensor
- Sensor positions
- T1 approx. 5 cm below ground (depending on the installation depth), T2 at the surface (+2 cm), and T3 +15 cm above ground. Installation guide
Unit architecture (TMS Standard)
- Three temperature sensors at fixed, standardized positions: in the soil (approx. -5 cm), at the surface (+2 cm), and at +15 cm - the profile of a small herbaceous plant.
- The soil moisture sensor runs along the buried stem, measuring the root zone. It reports raw units, used as-is in the scientific community - a relative moisture signal in which rain, drying, and drought stand out at a glance.
- The touch probe at the top connects to the TMD Adapter for configuration and data download - no exposed connectors, nothing to open.
- The sealed body - glass-filled nylon, filled with epoxy - has no buttons and no removable battery: the unit measures continuously from the factory, and in Basic mode has gone on doing so well past ten years in the field.
We call it simply the TMS, not by a model number. The hardware and firmware are improved continuously - usually small internal changes we never announce, which simply appear in the units we ship next. Measurements stay directly comparable across generations, so an old device and a new one belong in the same dataset without any conversion; put a TMS from five years ago beside one made today, though, and the difference is immediate, with more of it inside than out. It also means the units still recording after twelve years in the field are earlier hardware than anything leaving here now. The current generation (TMS-4) is the one described in the 2019 Agricultural and Forest Meteorology paper; earlier TMS-3 units remain fully supported in Lolly.
TMS variants
How the family fits together: the TMS Extreme is a variant of the TMS Standard, and every other variant except the TMS Dwarf is built on the Extreme. The Dwarf is a shortened Standard.
TMS Standard
The base unit measures temperature at three levels and soil moisture. It is installed into the ground with the reading probe just above the soil surface. The TMS Extreme is a variant of this unit, and every other variant except the Dwarf builds on the Extreme - so data stays directly comparable across the whole family. Sensor positions are listed in the technical specification above.
TMS Extreme
A variant of the TMS Standard with the same length and sensor placement, so the data stays directly comparable, but built for the harshest conditions - and the base the Long, Buriable, and Bend variants are built on. It carries a significantly larger, longer-lasting battery: rated by its manufacturer for 20 years of shelf chemistry against 10 on the other models, and in practice longer still.
- Higher-capacity memory (activated in a coming firmware update)
- Wider temperature measurement range
- Filled with glass-filled epoxy to the very top, so animals (e.g. wild boar) cannot chew off the top
- The one model that gains from a slower mode: with this much battery reserve, fewer readings can keep it logging well beyond a decade. On the other models, reading less often does not save the battery.
TMS Long
An extended version built on the TMS Extreme, with a longer tube available in several lengths. Depending on how it is fitted, it lets a sensor reach either deeper below the ground or higher above it.
TMS Buriable
Built on the TMS Extreme: a split design joined by a protected cable - an underground section (soil moisture sensor plus two temperature sensors) and an upper part (download contact plus the third temperature sensor).
TMS Dwarf
A shortened TMS Standard for placements where the reduced length is required - the one variant not built on the Extreme.
TMS Bend
A bent version built on the TMS Extreme, for installations where a straight body will not fit. It provides the same long-term microclimate measurements (air/soil temperature and soil moisture) with easier placement in constrained terrain.
Custom variants
The listed versions are what we keep as standard, but they are not the only thing we can build. Most of the range began exactly this way: the TMS, the Point Dendrometer and many of the variants exist because a research project needed something that did not exist yet. If your deployment needs something the standard range does not cover, write to us at tomst@tomst.com and we will discuss what is possible.
Why choose TMS dataloggers?
- Measures air + soil temperature and soil moisture in one compact device.
- Mimics an herbaceous plant (approx. 15 cm above and 5 cm below the surface) for ground-level microclimate monitoring.
- Minimal maintenance thanks to long battery life and large memory.
- Suitable for harsh environments - deployed on every continent, from tropical rainforests to high mountains.
- Data is downloaded with the TMD Adapter and Lolly.
- Standardized sensor placement allows strong comparability across deployments.
- Described in a peer-reviewed scientific publication: Agricultural and Forest Meteorology.
Installation tips
To measure properly, ensure the entire belowground (green) section is in good contact with the soil. In some soils, air pockets can form and reduce accuracy. Drying soils (e.g. clay) can shrink or swell, reducing contact and causing soil moisture values to appear lower.
Adjust installation to your soil type: in rocky soils, forcing the logger into the ground can damage sensors. Create a pilot hole first using a metal plate or the TMS Installation Tool, then insert the logger. If using a larger hole, cover it carefully with soil - this may slightly alter soil composition.
Frozen soil note
Do not use soil moisture data from periods when the soil is frozen. Frozen periods can be identified from the temperature sensor data.
How to install
Correct placement matters for accurate data. The buried (green) section must be in the soil, and the T2 surface sensor should rest just above the ground. Click any image to enlarge.
What gets buried
The whole green (belowground) section must be buried. The T2 surface sensor - marked by the small rivet - belongs right at the soil surface, so the collar just above the green section is usually buried too.
Horizontal installation
Where a vertical hole is not possible, the logger may be installed horizontally - but the green section still has to be fully in the soil. Do not simply lay it flat on the surface.
On a slope
On sloping ground keep the logger vertical (plumb), not perpendicular to the slope. The green section goes straight down into the soil.
Warning: never force the logger into hard, stony, or frozen ground - it can damage the sensors. Make a pilot hole first with the TMS Installation Tool.
Protection from wild animals
Most damage occurs when wild animals (deer, wild boar, bears) manipulate the devices. We recommend protecting the TMS with wire cages to prevent movement or damage.
After a wildfire
Dataloggers often come through a wildfire. Of the 25 at this site, 15 were still working after the fire. We have seen that many times, and it is still not something to count on - it depends on how the fire passed over the spot. From units that no longer work we can usually still recover the data; the exceptions are a device that is completely charred or one struck directly by lightning. A strike nearby is usually survived, which is a hard test for any electronics; a direct hit is not, and some units have come back completely charred.
Applications
Reference (citation)
Wild J., Kopecký M., Macek M., Šanda M., Jankovec J., Haase T. (2019) Climate at ecologically relevant scales: A new temperature and soil moisture logger for long-term microclimate measurement. Agricultural and Forest Meteorology, 268, 40-47. https://doi.org/10.1016/j.agrformet.2018.12.018