What it is

The Optris CTi LTfast is a two-piece infrared thermometer for precise and fast non-contact temperature measurement from –58 °F to 1,922 °F (–50 °C to 1,050 °C) in the 8–14 µm spectral range. Optris describes it as one of the smallest infrared sensors worldwide, with response times down to 6 ms. Its rugged 0.55 in (14 mm) sensing head is built for low target temperatures and is usable up to 257 °F (125 °C) ambient without cooling. The head connects by cable to an electronics box with programming keys, a backlit LCD display, and a built-in USB interface for setup via mobile phone or PC.

• Temperature range: –58 °F to 1,922 °F (–50 °C to 1,050 °C) across three models
• Spectral range: 8–14 µm
• Response time: 30 ms (LT02F), 9 ms (LT15F), 6 ms (LT25F)
• Optical resolution: 2:1 (LT02F), 15:1 (LT15F), 25:1 (LT25F)
• Measurement uncertainty: ± 1% or ± 3.6 °F (± 2 °C), whichever is greater
• NETD: 40 mK (LT02F), 75 mK (LT15F), 180 mK (LT25F)
• Smallest spot: 0.02 in at 0.4 in (0.6 mm at 10 mm), LT25F with CF lens
• Sensing head: 0.55 in (14 mm) diameter × 1.10 in (28 mm) length; up to 257 °F (125 °C) ambient without cooling
• Environmental rating: IP65 (NEMA-4). See the note in the Specifications tab
• Outputs: two analog outputs (0/4–20 mA, 0–5/10 V, thermocouple K, alarm); built-in USB
• Power supply: 8–30 V DC / 1.2 W

What it is used for

Some of the use cases for the Optris CTi LTfast include:

• Fast processes: temperature measurement with response times down to 6 ms.
• Moving or intermittent targets: objects passing the sensor on a line, where a slower sensor would average across the target and its background.
• Low target temperatures: measurement from –58 °F (–50 °C).
• Distance measurement: up to 25:1 optical resolution with the LT25F.
• Small targets: spots down to 0.02 in (0.6 mm) with the LT25F and the CF lens.
• Tight installations: fitting the 0.55 in (14 mm) head into confined locations, with the electronics box sited remotely.

The model range

Model choice on the LTfast is a trade between speed and noise. The LT25F is the fastest at 6 ms but has the highest NETD at 180 mK and the widest repeatability at ± 0.99 °F (± 0.55 K). The LT02F is the slowest at 30 ms and the quietest at 40 mK, with repeatability of ± 0.20 °F (± 0.11 K), though it tops out at 1,112 °F (600 °C) rather than 1,922 °F (1,050 °C). Pick the slowest model your process will tolerate.

Temperature ranges are scalable via the programming keys or software and app. Full optical, electrical, and environmental data is in the Specifications tab.

Key features

• Fast response: down to 6 ms on the LT25F.
• Very small sensing head: described by Optris as one of the smallest infrared sensors worldwide.
• Rugged head for low target temperatures: usable up to 257 °F (125 °C) ambient without cooling.
• Three optical resolutions: 2:1, 15:1, and 25:1, with an optional CF lens for small objects.
• Two-piece design: separate sensing head and electronics box with easily accessible programming keys and a backlit LCD display.
• Built-in USB interface: simple sensor setup via mobile phone or PC.
• Selectable analog outputs: two outputs, each 0/4–20 mA, 0–5 V, 0–10 V, or thermocouple type K, plus an alarm output.
• Optional fieldbus interfaces: EtherNet/IP, Profinet, EtherCAT, Ethernet TCP/IP with Modbus TCP, Modbus RTU, RS485, RS232, or two optically isolated relay outputs. IO-Link is listed among the optional interfaces in the datasheet feature list.
• Three programmable I/O pins: external emissivity adjustment, ambient temperature compensation, uncommitted value, trigger (reset of hold functions), or alarm output.
• Signal processing: peak hold, valley hold, and averaging, plus extended hold functions with threshold and hysteresis.
• Easy sensing head exchange: heads can be exchanged within a model group by entering the head's calibration code into the electronics box.
• Software and app: configuration through Optris CompactPlus Connect software or the IRmobile app.

Why engineers pick it

Speed in the 8–14 µm range. Response times of 30, 9, or 6 ms depending on model, where the standard CTi LT runs at 40 to 115 ms in the same band.

Low temperatures included. Measurement from –58 °F (–50 °C), so the same sensor family covers cold targets and process heat to 1,922 °F (1,050 °C).

Simple setup. Programming keys, a backlit LCD display, and USB setup via phone or PC.

Flexible integration. Two analog outputs, three programmable I/O pins, and optional industrial Ethernet, fieldbus, and relay interfaces.

Frequently asked questions

Can I use the CTi LTfast as a 2-wire sensor?

No. Do not connect a supply voltage to the analog outputs, as this will destroy the output. The CTi LTfast is not a 2-wire sensor. If you need a two-wire device, review the Optris CSmicro series instead.

What distance-to-spot size ratio is correct for my application?

The size of the measuring object and the thermometer's optical resolution determine the maximum distance between the sensing head and the object. To prevent measuring errors, the object should fill the field of view of the optics. The spot should always be the same size as the object or smaller.

Which settings change if an external close-focus lens is used?

The optional CF lens allows measurement of small objects. When it is fitted, transmission must be set to 0.78. That figure is an average characteristic value and may scatter between units, so determine it experimentally if your application requires it.

Can I shorten the cable between the sensing head and the electronics box?

It is not recommended, because the cable's impedance forms part of the sensor calibration. On all CTi LTfast models the sensing head cable can be shortened if necessary, but doing so introduces an additional measuring error of about 0.1 K per metre removed.

How do I exchange the sensing head?

Heads are connected and calibrated at the factory. Any exchange of sensing heads and electronics is possible within a given model group. Every head carries a specific calibration code printed on the head cable, and that code must be stored in the electronics box for correct temperature measurement and sensor functionality.

How can I improve the noise amplitude of the sensor?

Do not move the head cable during measurement. Use shielded cables only and ground the sensor shield. Avoid ground loops and related signal interference in industrial environments. It may be necessary to interrupt the ground connections inside the electronics box by switching the internal jumper to another position. Review the manual before doing so.

Configuring and scaling

Select the model and cable length on this page and use Request Quote to order. Cable lengths are 3.3 ft (1 m) standard, 9.8 ft (3 m), 26.2 ft (8 m), or 49.2 ft (15 m). Contact W5 for anything the selector doesn't cover, such as optional digital interfaces, relay outputs, and the CF lens.

Scope of supply

CTi LTfast with a 3.3 ft (1 m) cable, mounting nut, and quick start guide.

Choosing between the CTi LTfast and the CTi LT

Both cover –58 °F to 1,922 °F (–50 °C to 1,050 °C) in the 8–14 µm band on the same 0.55 in (14 mm) head. Choose the LTfast when process speed is the constraint: 6 to 30 ms against 40 to 115 ms. Choose the standard CTi LT when accuracy matters more than speed. Its measurement uncertainty is ± 1.8 °F (± 1 °C) against ± 3.6 °F (± 2 °C), its NETD reaches 25 mK against 40 mK, and its head tolerates 356 °F (180 °C) ambient against 257 °F (125 °C).

Get the CTi LTfast specified and supplied

W5 Engineering supplies Optris infrared temperature measurement products. We match the model to your process speed, temperature range, target size, and working distance, then specify the optics, cable length, and any fieldbus interface you need. Contact us with your application details and we will return a configuration recommendation and quote.