TMP117 Waterproof Digital Temperature Probe

The FST-TMP117 is a sealed digital temperature probe built around the original Texas Instruments TMP117 chip. It reports temperature over I2C with 0.0078 °C resolution. The chip is rated ±0.1 °C maximum from –20 °C to 50 °C. The probe seals it in a SUS304 or SUS316 steel tube rated IP67, on a 4- to 6-wire cable up to 5 m long. Every probe is tested and carries an ID label.

Since 2022 Focusens has supplied TMP117 probes to medical device makers in Western and Northern Europe.

Key specifications

Chip accuracy and probe accuracy are not the same number

The ±0.1 °C figure belongs to the TMP117 chip. Once the chip is sealed in a steel tube, three things add to it: the thermal path through the tube wall and epoxy, heat conducted along the tube and cable from the surroundings, and the uncertainty of whatever reference you compare against. In air or in a fast-changing liquid the probe also reads more slowly than a bare chip on a board.

Self-heating is small. At 3.3 V and one conversion per second the chip averages about 3.5 µA, roughly 12 µW (our calculation).

The chip itself works from –55 to 150 °C. The probe is rated –50 to 125 °C because the epoxy, heat-shrink and cable set the limit, not the chip.

Replacing a PT100 with a TMP117 probe

Focusens offers this probe as a higher-accuracy replacement for a PT100, PT500 or PT1000 where the host can read a digital signal. Between –20 and 50 °C the TMP117 chip is specified at ±0.1 °C maximum. A Class A platinum element alone is allowed ±(0.15 + 0.002|t|) °C under IEC 60751, which is ±0.2 °C at 25 °C, before the transmitter adds its own error.

The TMP117 probe gives a digital I2C reading. It replaces the RTD and its transmitter or ADC together, so the host needs an I2C input instead of a resistance input.

Ordering code

FST – TMP117 – (3) cable – (4) length – (5) housing – (6) pull-up – (7) wiring and address

Example from the Focusens datasheet: FST-TMP117-CPR-162-1650-1-5A is a probe with –40 to 105 °C PVC cable, 1.6 m long, in a SUS304 Ø6 × 50 mm tube, with a built-in 5.1 kΩ pull-up, 5 wires including ALERT, at I2C address 0x4A.

Wiring

Wire colors on the 6-core silicone cable

Dimension drawing and wire colors of a TMP117 probe with 6-core silicone cable.

On this cable black is SCL and white is GND. Check the colors before you power up. Other cable types can use different colors, so check the drawing that comes with your order.

Up to four probes can share one I2C bus, one per address.

Cable length and I2C

We normally keep the I2C cable within 5 m. Every meter of cable adds capacitance, and standard I2C allows up to 400 pF per bus (NXP UM10204). If you need a longer run, tell us the length and the host you use before ordering.

Probe not detected on the I2C bus?

The two most common causes we see:

1. The cable is too long. Shorten it, or lower the I2C clock rate.
2. The pull-up is wrong. A pull-up resistor with too high a value makes the signal edges too slow. If you ordered a probe with the built-in 5.1 kΩ pull-up (code 1), do not add another pull-up on your board. Two pull-ups in parallel lower the total resistance, and the bus may stop reading.

If readings still look wrong, send us the ordering code, cable length and host board, and our engineers will help find the cause.

Applications

• Medical devices and medical temperature logging
• Laboratory equipment and biological incubators
• Precision instruments
• Wireless environmental sensors, IoT nodes and thermostats
• Automotive test equipment
• A reference probe for checking other sensors in the same space

FAQ

Is a TMP117 probe more accurate than a DS18B20 probe?

At the chip level, yes. TMP117 is rated ±0.1 °C maximum from –20 to 50 °C. DS18B20 is rated ±0.5 °C from –10 to 85 °C (Analog Devices datasheet). In a sealed probe both numbers grow with the housing and installation.

Can TMP117 be used in a waterproof probe?

Yes. The chip itself is a small surface-mount part, so it needs a sealed housing. This probe seals it in a SUS304 or SUS316 tube with epoxy, rated IP67, and IP68 is available on request.

What temperature range can the probe handle?

The chip works from –55 to 150 °C. With silicone cable the probe is rated –50 to 125 °C. With PVC cable the cable sets a lower limit, from 85 °C to 105 °C depending on the type.

How long can the cable be?

Standard lengths go up to 5 m, and we normally keep I2C runs within 5 m. Longer runs need a lower clock rate or a bus extender.

Is the probe NIST traceable?

Texas Instruments tests every TMP117 on a NIST-traceable production setup. Focusens tests and ID-labels every probe, and can supply calibration records per probe or per batch on request.

Does it meet medical thermometer standards?

Texas Instruments states that the TMP117 chip meets ASTM E1112 and ISO 80601-2-56. That statement covers the chip. The assembled probe needs its own testing in your device.

Can I get the same probe with TMP119, TMP118 or TMP116?

Yes. TMP119 is pin-compatible with TMP117 and rated ±0.08 °C maximum from 0 to 45 °C. TMP118 is a smaller, lower-power option rated –40 to 125 °C. TMP116 is the earlier generation, rated ±0.2 °C maximum from –10 to 85 °C.