What it is

The Optris CTi LThot is a two-piece infrared thermometer for precise non-contact temperature measurement from –58 °F to 1,922 °F (–50 °C to 1,050 °C) in rough environmental conditions. Its sensing head works in hot environments up to 482 °F (250 °C) without any need for cooling. It suits dryers, ovens, and heat treatment lines in the metal and glass industry, as well as paper, plastic, and textile manufacturing and semiconductor processing. The head sits in a massive housing and connects by cable to an electronics box with programming keys, an LCD display, and a built-in USB interface. Response time starts at 40 ms.

• Temperature range: –58 °F to 1,922 °F (–50 °C to 1,050 °C), both models
• Spectral range: 8–14 µm
• Optical resolution: 2:1 or 10:1
• Smallest spot: 0.12 in at 1.2 in (3.0 mm at 30 mm), LThot 10:1 with CF1 lens
• Measurement uncertainty: ± 2.7 °F (± 1.5 °C) or ± 1%, whichever is greater
• NETD: 37 mK (2:1); 45 mK (10:1)
• Response time: 45 ms (2:1); 40 ms (10:1)
• Sensing head: massive housing, 1.16 in (29.5 mm) diameter, M18 × 1 thread; up to 482 °F (250 °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 LThot include:

• Dryers and ovens: measuring product temperatures inside hot equipment.
• Heat treatment lines: temperature monitoring in the metal and glass industry.
• Paper, plastic, and textile manufacturing: process temperature measurement in hot surroundings.
• Semiconductor processing: non-contact measurement across the full –58 °F to 1,922 °F (–50 °C to 1,050 °C) range.
• Machine integration: building the head into machinery where ambient temperatures rule out a standard sensor.
• Small targets: spots down to 0.12 in (3.0 mm) on the 10:1 model with the CF1 lens.

The model range

Both models cover the same temperature range, scalable via the programming keys or software and app. The choice is about optics and noise: the 2:1 gathers more energy for slightly better repeatability and NETD, while the 10:1 resolves smaller targets at distance and is the only model offered with the CF1 close-focus lens.

Key features

• Hot-environment sensing head: operates up to 482 °F (250 °C) ambient without cooling.
• Massive housing: the sensing head is supplied in a massive housing with an M18 × 1 thread.
• Close-focus option: CF1 lens for a 0.12 in (3.0 mm) spot at 1.2 in (30 mm) on the 10:1 model.
• Low noise: NETD of 37 mK (2:1) or 45 mK (10:1).
• Two-piece design: separate sensing head and electronics box with easily accessible programming keys and an LCD display.
• Built-in USB interface: for connection to Optris CompactPlus Connect software or the IRmobile app.
• 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.
• 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 ID into the electronics box.
• Software and app: configuration through Optris CompactPlus Connect software or the IRmobile app.

Why engineers pick it

No cooling up to 482 °F. The sensing head works in ambient temperatures up to 482 °F (250 °C) without cooling, removing the air or water supply a cooling jacket would otherwise require.

Built for rough conditions. Designed for dryers, ovens, and heat treatment lines, with a massive housing that minimizes thermal gradients along the head.

Simple setup. Programming keys, an LCD display, and a built-in USB interface for configuration from a phone or PC.

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

Frequently asked questions

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 LThot 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, with the Head ID already entered. Any exchange of sensing heads and electronics is possible within a given model group. Every head carries a specific Head ID, printed on the head cable and engraved on the sensing head. This calibration code must be stored in the electronics box for correct temperature measurement and sensor functionality.

Can you connect two pyrometers to the same computer?

Yes. Using CompactPlus Connect or CompactConnect, depending on which pyrometers you have, you create separate instances of the software. Two pyrometers can be connected via the USB ports. Connection over RS485 is also possible, with the first pyrometer connected to the PC through the supplied RS485-to-USB adapter.

Configuring and scaling

Select the model and cable length on this page and use Request Quote to order. Cable lengths are 9.8 ft (3 m) standard, 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 CF1 lens.

Scope of supply

CTi LThot with mounting nut, a 9.8 ft (3 m) high-temperature head cable, and a quick start guide.

Choosing between the CTi LThot and the CTi LT

Both cover –58 °F to 1,922 °F (–50 °C to 1,050 °C) in the 8–14 µm band. Choose the LThot when ambient temperature at the mounting point exceeds 356 °F (180 °C), up to its 482 °F (250 °C) limit. Choose the standard CTi LT when you need a smaller head, 0.55 in (14 mm) against 1.16 in (29.5 mm), finer optical resolution up to 22:1, or spots below 0.12 in (3.0 mm).

Get the CTi LThot specified and supplied

W5 Engineering supplies Optris infrared temperature measurement products. We match the model to your process temperature, ambient conditions at the mounting point, 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.