Installing in High Temperatures: Blocking Radiation, Dissipating Heat, Split Mounting and Cable Selection

Sensor failures in high-temperature environments are rarely caused by the unit being "baked". They come from accelerated ageing and persistent temperature drift when the sensor works for long periods near its rated upper limit. Four things can be done on the installation side: blocking radiant heat, improving heat dissipation, moving the electronics head out of the hot zone, and selecting temperature-rated cable. Moving the electronics head out of the hot zone is the most direct measure, and is the reason split-type models exist. This article sets out the installation sequence and the criteria for judging high-temperature applications. For how to read temperature ratings, see operating temperature vs. storage temperature; for selection-side constraints, see high-temperature selection.

Distinguish three temperatures before mixing them in discussion

When people on site talk about "high temperature", they are often not referring to the same thing. Confirm each separately:

• Ambient temperature: the air temperature around the electronics head, which sets the working conditions for the electronic components;
• Medium temperature: the hydraulic-oil temperature in which a cylinder-integrated rod is immersed, which sets the working conditions for the rod and seals;
• Radiant heat: radiation from nearby furnaces, castings or hot steel billets, which can locally raise surface temperature far above the surrounding air temperature.

The three constraints are different, and the datasheet maps them to different parameters. On metallurgical, forging and die-casting sites the third is the one most often missed — the air temperature looks modest, yet the sensor faces a heat source and its actual surface temperature far exceeds expectations.

Step 1: block radiation

This is the lowest-cost, fastest measure. Fitting a reflective heat shield (metal plate plus an air gap) between the sensor and the heat source can cut radiant heat input substantially. The essential point is that an air-flow gap must be left between the shield and the sensor; otherwise heat builds up in the cavity and the situation becomes worse. The measure is especially effective on metallurgical rolling mills, continuous casters and forging lines.

Step 2: manage convective cooling

Keep air moving around the sensor. Practical means include: not enclosing the sensor in an unventilated cover; introducing compressed-air purging or vortex-tube cooling where needed; and moving the mounting position off the path of rising hot air. A detail that is often overlooked: hot air collects upwards. On the same machine, the temperature difference between a high mounting and a low one can be considerable — if you can move it down, do so.

Step 3: split-type — move the electronics head away

When the ambient temperature genuinely exceeds what an integral model can tolerate, the correct solution is a split-type unit: the rod stays in the hot zone, and the electronics head is mounted via a connecting cable in a cooler location. The 19D split-type is designed for this duty. Points to watch when installing a split-type sensor:

• The electronics-head location must be genuinely cool — do not merely shift it half a metre and leave it in the hot-air stream;
• The section of connecting cable that still sits in the hot zone must be specified for temperature and given heat shielding;
• The electronics head must remain accessible for later maintenance; do not tuck it into an unreachable corner simply to avoid heat.

Step 4: cable selection and routing

The cable is often the first part to fail in high-temperature duty — the sheath hardens, cracks and insulation drops, then data loss or an open circuit follows. Selection points:

For connector and seal maintenance, see selecting waterproof M12 connectors and maintaining seals.

Effect on the measurement itself: temperature drift must have a planned response

Even when the sensor stays within its permitted temperature range, the reading still changes with temperature: the speed of sound in the waveguide (about 2830 m/s) varies with temperature, and the mechanical structure also expands. Together they produce zero and span drift. There are three engineering responses: perform zero calibration only after the system has reached a stable working temperature (see zero calibration step by step); introduce temperature compensation on the controller where accuracy is demanding; and, on long-stroke equipment, fix one end of the mounting and leave the other floating to relieve thermal-expansion stress (see external installation). For the underlying mechanism, see self-heating, thermal equilibrium and the magnitude of temperature effects.

Selection notes when high temperature stacks with other conditions

Sites rarely have high temperature as the only constraint. Common combinations: high temperature plus high pressure (cylinder-integrated types must meet both the 300 bar / 600 bar pressure rating and the temperature; see high-pressure cylinder selection); high temperature plus dust (consider Ex tD dust explosion protection and the ingress-protection rating); high temperature plus wash-down (IP69K protection is required, as on the Series 13 mobile hydraulics). For high-temperature cylinder-integrated applications, check the specification limits of the Series 17 hydraulic-cylinder integrated and the Series 16 cylinder-integrated; if those limits are exceeded, prefer a split-type solution.