How to Install an Explosion‑Proof Temperature Transmitter Correctly?

When you need to measure temperature in hazardous areas – think petrochemical plants, oil refineries, or grain silos – a standard temperature transmitter won’t do. You need an explosion‑proof device that can withstand flammable gases, vapours, or dust while delivering accurate, stable readings. But how do you install such a transmitter safely and correctly? In this guide, we’ll walk through the installation of the HTM208 Explosion‑Proof Temperature Transmitter using real‑world best practices.

What Makes the HTM208 Different?

The HTM208 is designed for tough industrial environments. It uses a PT100 or thermocouple sensor and offers:

• Temperature range – from –196°C up to +1500°C (depending on the sensor)

• Accuracy – ±0.5% FS

• Output options – 2‑wire 4‑20mA, RS485, or HART

• IP66 aluminium housing – dust‑tight and protected against powerful water jets

• Long‑term stability – ±0.2% FS/year

• Built‑in protection – reverse polarity, overcurrent, and overvoltage

Its rugged construction and safety certifications make it a popular choice for Zone 1 and Zone 2 explosive atmospheres.

Step‑by‑Step Installation

1. Choose the Right Mounting Position

• Install the transmitter close to the process but away from direct heat radiation or strong vibration.

• The standard process connection is threaded (M20×1.5). Other options include G1/2, M27×2, tri‑clamp, or flange.

• Use a valve between the process and the transmitter – this allows removal without shutting down the whole line.

Tip: Always tighten the transmitter using a wrench on the hexagon of the body, not on the housing or electrical connection.

2. Prepare the Explosion‑Proof Housing

• Before installation, ensure the housing cover is fully tightened. A loose cover breaks the explosion‑proof seal.

• The housing is cast aluminium alloy. Both the internal and external grounding screws must be reliably grounded – this is mandatory for safety.

3. Make the Electrical Connections

The HTM208 uses a 2‑wire 4‑20mA loop (or RS485 / HART). Follow these rules carefully:

• Use certified cable glands that match the hazardous area classification.

• Connect the wires to the terminal block, then secure the anti‑loosening workpieces at both ends of the cover – tilt them at a slight angle and tighten the locking screws.

• The free end of the cable must be connected to an explosion‑proof device that is certified for the same zone.

Power supply limits:

• Allowable load resistance: 0–600Ω at 24V (including cable resistance). Exceeding this may cause output errors.

4. Check the Environmental Conditions

• Ambient temperature for explosion‑proof models: –40°C to +60°C.

• Working humidity: ≤90% at +25°C.

• Altitude: ≤2000m.

• Atmospheric pressure: 86–106 kPa.

Staying within these limits is essential to keep the explosion‑proof certification valid.

5. Perform Final Safety Checks

• Verify that the insertion depth and thread match your process connection.

• Ensure the sensor (PT100 or thermocouple) is compatible with the medium – wetted parts are 304 or 316L stainless steel.

• Do a visual inspection: no damaged cables, tight covers, proper grounding.

Critical Safety Rules for Explosion‑Proof Models

Working in hazardous environments leaves no room for shortcuts. Always follow these principles:

Common Mistakes to Avoid

• Over‑tightening the thermowell – This can damage threads or distort the sensor tip.

• Ignoring cable length – Long cables increase resistance; keep within 0–600Ω load limit.

• Mounting the housing upside down – Condensation may enter; orient the cable entry downward.

• Forgetting the grounding screw – A floating ground invites electrical noise and reduces safety.

Real‑Life Example

A chemical plant needed to monitor reactor temperature in a Zone 1 explosive gas area. They chose the HTM208 with a PT100 sensor, 4‑20mA HART output, and a cooling cone to protect the housing from radiant heat. After grounding both screws and using approved cable glands, the system passed a strict site inspection and has run fault‑free for over 18 months.

Final Thoughts

Installing an explosion‑proof temperature transmitter isn’t difficult – but every detail matters. Follow the manufacturer’s instructions, respect the safety rules, and test the loop before putting it into service. The HTM208 combines robust hardware with flexible outputs, making it a reliable choice for demanding temperature control applications.

Need help selecting the right sensor or configuring your loop? Contact us – we offer free technical advice and support.

Stay safe and measure accurately!