Same measurement, different place to live
Both sensor types read the same two things: pressure and air temperature inside the tire. On our platform the accuracy figure is the same for either — ±7 kPa on pressure and ±3 °C on temperature. So if you are choosing between internal and external on accuracy, you are choosing on the wrong axis.
The real difference is where the sensor spends its life. An internal sensor is mounted inside the tire, on the rim or on a valve stem that reaches the drop centre. An external sensor screws onto the valve from outside. Everything that follows — service model, temperature range, battery life, survival rate — comes from that one decision.
Internal sensors
What it is. Mounted on the rim inside the tire. Nothing is visible from outside the wheel. Nothing can be knocked off by a kerb, a rock or a careless tyre iron.
Temperature range. −40 °C to +125 °C. That range is not a marketing number; it is what a sensor has to survive when it sits in the air chamber of a tire that is being worked hard.
Battery. Five to six years or more, because the cell can be large and the sensor is not fighting external heat.
Service model. Fitting and replacing requires breaking the tire off the rim. That is a tire-shop job, which is fine if you already break tires on a schedule and a problem if you do not.
Where it belongs. Mining haul trucks, port equipment, beam carriers and any machine where wheels are exposed to impact. This is the default choice for heavy industry for a reason: once it is in, it stays.
External sensors
What it is. A cap on the valve stem, fitted and removed by hand.
Temperature range. −20 °C to +85 °C. Less extreme than internal, which is enough for most surface ambient conditions and not enough to sit inside a hot tire.
Battery. A CR1632 cell gives at least two years, and it is replaceable in the field. This is the strongest argument for external: a flat battery costs you minutes, not a tire service visit.
Service model. No tire work, no special tools, no downtime for the machine beyond the time it takes to walk around it.
Where it belongs. Fleets where deployment speed matters, where tyres are changed frequently, and where the wheel face is protected. Also useful as a temporary measurement on a machine you are still evaluating.
What to watch. External sensors are exposed to impact, washdown, corrosion and, on unattended sites, removal. They also add mass to the end of the valve stem, so the stem and its support have to be suitable — a detail worth confirming with the vehicle's tyre fitter rather than assuming.
The five questions that actually decide it
Work through these in order. The answer usually falls out by question three.
1. Who breaks your tires, and how often? If tire work already happens on a planned interval, internal sensors add almost no burden and can be replaced at the same time. If the machine never sees a tire shop, external wins by default.
2. How exposed is the wheel face? Rock strikes, kerbs, loaders working close to the wheel, and spillage all argue for internal.
3. What are the ambient and duty conditions? Extreme cold, high ambient heat, or a duty cycle that keeps tires hot will push you toward the internal sensor's wider rating. Washdown and salt argue against exposed hardware.
4. How fast do you need coverage? Fitting external sensors on 200 wheels can be done by your own fitters in a shift. Fitting internal sensors on the same machine is a scheduled workshop event.
5. Who owns the data for the next five years? A battery change is a maintenance task. Ask who performs it, on which machine, and whether the sensor ID mapping survives it.
Mixed fleets are normal
There is no rule that says one machine must use one type. A common and sensible arrangement is internal sensors on the driven and heavily loaded axles, and external sensors on trailers and lightly loaded positions. Another is internal on production machines and external on the units still being evaluated.
What must not be mixed casually is the configuration record. If both types are in service, the ID list has to say which is which, or the next person to change a battery will create a mystery.
What matters more than the sensor type
Three things will affect your project more than the internal-versus-external decision.
Repeater planning. On a long chassis the radio path, not the sensor, is the constraint. Our production configuration for a 160-wheel beam carrier uses two receivers and twelve repeaters, and the largest single machine we have instrumented carries 224 wheels across 28 axles.
The interface. A sensor with perfect accuracy and no message map is still an integration problem. CAN 2.0B at 250 kbps with a 500 ms data period is our default, configurable in software, alongside J1939, RS485, RS232, Modbus RTU, PROFINET and UART.
The mounting hardware. Valve stem type, rim profile, whether there is a drop centre to mount into. This is where industrial TPMS projects lose weeks. Send photographs of the rim and the valve, not just the drawing.
Enclosure and environment
Both sensor types we supply are sealed to IP68, and both radios run on 433.92 MHz licence-free. The gateway and receiver are built for machine supply, DC 10–30 V, which covers both 12 V and 24 V systems without a converter.
If the machine is washed down, if it works in a corrosive atmosphere, or if it is pressure-washed by hand at the wheel face, say so early. It changes the mounting recommendation more often than it changes the sensor.
What we verify
We verify pressure calibration on every unit, run water immersion, verify the radio link over distance, run full wheel-count system integration, age the electronics under power, and verify CAN and serial protocol behaviour. Those are the checks we actually perform; the results ship with the configuration.
See the TR100 sensor and receiver specification, read the mining TPMS application page, or look at the mining truck installation.
How to choose in one step
If your tires already get broken on a schedule and the wheels take a beating, go internal. If nothing breaks your tires and a flat battery should cost you minutes rather than a workshop slot, go external. If you are unsure, tell us the machine, the rim, and who does the tire work. Send those three details and we will recommend one — and explain what changes if we are wrong.