Bayonet RTD Assemblies Adjustable Length: When Do You Need a 75mm Tip Instead of 50mm for Your Extruder?

If you’ve browsed Aavad’s bayonet RTD range and noticed two Spring Bayonet RTD models that look almost identical — the APES_5X65 with a 50mm tip and the APES_5X75 with a 75mm tip — and you’re trying to figure out which one your extruder needs, this guide gives you the definitive answer. Tip length selection is the single most common bayonet RTD ordering error in Indian plastic processing plants, and it’s made worse by the fact that most catalogue listings don’t explain why two tip lengths exist and how you determine which is correct for your specific machine.

What Is a Bayonet RTD Assemblies Adjustable Length Sensor?

The Bayonet RTD Assemblies Adjustable Length (APES_5X75) is a PT100 Class A, 3-wire, spring-loaded bayonet resistance thermometer for plastic extruder barrel zone temperature measurement — identical in function and cap geometry to the Spring Bayonet RTD (APES_5X65), but with a 75mm tip rather than 50mm and a slightly different cable construction (TF/TF without SS braid rather than TF/TF/SS). The “adjustable length” designation refers to the adjustable threaded spring that allows the bayonet cap to be locked at the correct pre-load position for different recess depths.

Full Specifications: Aavad APES_5X75 Bayonet RTD Adjustable Length

The Core Question: When Do You Need 75mm Instead of 50mm?

Understanding Extruder Recess Geometry

A bayonet extruder sensor recess has two key dimensions:

1. Bore diameter — the drilled hole diameter that accepts the sensor tip. This is determined by the tip OD (5mm for the APES_5X75, also available in 4.7mm and 6mm variants).
2. Bore depth — how deep the drilled hole goes into the barrel material from the surface where the bayonet cap seats. This determines which tip length you need.

The 50mm Tip (APES_5X65)

The 50mm tip on the APES_5X65 Spring Bayonet RTD is correct when:

• Your extruder barrel’s sensor well depth is approximately 30mm–50mm from the bayonet cap seating surface
• The spring, when pre-loaded by 10–15mm compression, positions the 50mm tip comfortably within this depth
• Common on: modern Asian-manufactured extruders in the sub-80-tonne clamping force class, many twin-screw extruders, and compact extruder designs with shallow barrel section thicknesses

The 75mm Tip (APES_5X75)

The 75mm tip on the APES_5X75 Adjustable Length RTD is correct when:

• Your extruder barrel’s sensor well depth is approximately 55mm–75mm from the cap seating surface
• A 50mm tip would not reach the well bottom when the spring is at correct pre-load compression — the tip would be partially suspended in the bore rather than contacting the bottom
• Common on: larger extruders with thicker barrel sections, European OEM machine designs, older extruder generations with deeper drilled recesses, and injection molding machines with longer barrel heating zone dimensions

How to Measure Your Recess Depth

1. Remove the existing sensor from the recess
2. Insert a thin rod or calibrated depth gauge into the empty recess until it contacts the bottom
3. Measure from the bottom contact point to the seating surface where the bayonet cap face makes contact
4. If this depth is 50mm or less → specify 50mm tip (APES_5X65). If 50mm–75mm → specify 75mm tip (APES_5X75). If greater than 75mm → contact Aavad for a custom tip length

Cable Difference: TF/TF vs TF/TF/SS

The APES_5X75 uses Teflon/Teflon (TF/TF) cable without the stainless steel braid that the APES_5X65 (TF/TF/SS) includes. In practical terms:

• TF/TF (APES_5X75): Teflon insulation on inner conductors and outer jacket — provides chemical resistance and heat resistance up to the Teflon operating limit. Flexible, lightweight, suited to applications where the cable is neatly routed within machine cable trays.
• TF/TF/SS (APES_5X65): Adds a stainless steel braid over the Teflon jacket — provides additional mechanical protection against abrasion, crushing, and accidental contact damage, plus some EMI shielding. Better for exposed cable runs, more congested machine environments, or installations where cables may contact moving parts.

For most standard extruder barrel zone wiring within the machine’s cable management system, TF/TF is adequate. For exposed cable runs in harsher environments, the SS braid variant (APES_5X65) offers additional protection.

Comparing All Three Aavad Bayonet RTD Variants

Selection flowchart:

• Recess depth ≤50mm, want SS braid cable → APES_5X65
• Recess depth 50–75mm, standard cable adequate → APES_5X75
• Recess depth 50–75mm AND need long spring travel → APES_5X45
• Not sure → measure recess depth and contact Aavad to confirm

Why Tip Length Error Causes Measurement Problems

Getting the tip length wrong is more than a fitment issue — it directly affects measurement accuracy:

Tip too short for the recess depth: The tip cannot reach the well bottom when the spring is at correct pre-load. The spring is fully extended, providing no contact force on the tip. The tip floats in the air within the bore. An air gap forms between the tip and the well bottom — the sensor reads ambient air temperature in the bore rather than the barrel wall temperature. The controller sees a falsely low reading and drives the heater harder, overheating the barrel interior while the surface temperature sensor shows a “normal” setpoint reading.

Tip too long for the recess depth: The tip bottoms out in the well before the spring can compress to pre-load position. The bayonet cap cannot fully engage the locking pin. The sensor either cannot be locked at all, or locks in a partially-engaged position that vibration can disengage. Either way, the sensor is mechanically unstable and risks working loose during operation.

Correct tip length: The tip contacts the well bottom, the spring compresses 10–15mm below its extended length, and the bayonet cap locks securely. The spring maintains positive contact pressure throughout the thermal cycle.

Industries and Applications Across India

Plastic Extrusion — Blown Film, Pipe, Profile, Cable

Hubs: Ahmedabad, Rajkot, Vadodara (Gujarat) | Pune, Nashik (Maharashtra) | Noida, Greater Noida (UP) | Ludhiana (Punjab) | Chennai, Hosur (Tamil Nadu) | Hyderabad (Telangana) | Bengaluru (Karnataka)

Larger-format extruders and older European OEM machines commonly have the deeper 50–75mm recesses that make the 75mm tip the correct specification. The same slot-selection logic applies: count the pins in your recess (single or double slot cap selection from the same two options as APES_5X65).

Injection Molding — Large Clamping Force Machines

Hubs: Rajkot (Gujarat) | Pune (Maharashtra) | Noida, Faridabad (NCR) | Chennai (TN) | Ludhiana (Punjab)

Large injection molding machines (200 tonnes and above clamping force) typically have thicker barrel sections and deeper sensor recesses than smaller machines — making the 75mm tip the more common specification for these assets.

Rubber Processing

Hubs: Faridabad, Ballabhgarh (Haryana) | Vadodara (Gujarat) | Pune (Maharashtra) | Kottayam (Kerala)

Rubber extruder barrel temperature monitoring — where barrel wall thickness and recess geometry often match the 75mm tip specification.

OEM Replacement — European Machine Brands

Nationwide: European OEM extruders and injection molders (Battenfeld, Engel, KraussMaffei, Berstorff, Leistritz, Extricom brands common in Indian plastics plants) historically used deeper barrel recesses matching the 75mm tip length standard.

India-Wide Coverage

Aavad Instrument supplies Bayonet RTD Adjustable Length Sensors PAN India from Ahmedabad:

Gujarat: Ahmedabad, Vadodara, Surat, Rajkot, Ankleshwar, Vapi, Morbi, Bharuch, Gandhinagar, Jamnagar, Mehsana

Maharashtra: Pune, Nashik, Mumbai, Aurangabad, Nagpur, Kolhapur

Delhi NCR: Noida, Greater Noida, Faridabad, Gurugram | Haryana: Faridabad, Ballabhgarh, Gurugram

Tamil Nadu: Chennai, Coimbatore, Hosur, Sriperumbudur | Karnataka: Bengaluru, Mysuru

UP: Noida, Kanpur, Lucknow | Punjab: Ludhiana, Amritsar, Mohali

Kerala: Kochi, Kottayam | Rajasthan: Jaipur, Bhiwadi, Alwar

Telangana & AP: Hyderabad, Visakhapatnam | WB, MP, Jharkhand, Odisha, HP, Uttarakhand, Goa, Bihar, Assam: PAN India

Aavad Instrument: India’s #1 Bayonet RTD Manufacturer

Aavad Instrument Pvt. Ltd., Chandkheda, Ahmedabad, Gujarat:

• ISO 9001:2015 certified | NABL-accredited calibration laboratory
• 15+ years | 38M+ installations | 2,900+ customers | 12+ countries
• Trusted by Sintex, PepsiCo, Kohler, BHEL, L&T, Aditya Birla Group, Saint-Gobain

Frequently Asked Questions

Q1. What is the difference between the 50mm and 75mm tip bayonet RTD sensors?

The tip length must match your extruder’s sensor well (recess) depth. A 50mm tip is for recesses ≤50mm deep; a 75mm tip for recesses 50–75mm deep. Using the wrong tip length causes the sensor tip to either float in the bore (false low reading) or bottom out before the spring reaches pre-load (loose, unstable installation).

Q2. How do I measure my extruder’s recess depth to choose the right tip?

Remove the existing sensor and insert a calibrated depth gauge or thin rod into the empty recess until it contacts the bottom. Measure from that point to the bayonet cap seating surface. That measurement is your recess depth — match it to the tip length accordingly.

Q3. What is the difference in cable between APES_5X65 and APES_5X75?

APES_5X65 uses TF/TF/SS (Teflon/Teflon with SS braid) offering additional mechanical protection and EMI shielding. APES_5X75 uses TF/TF (Teflon/Teflon, no braid) — adequate for neatly routed cable within machine cable management; lighter and more flexible.

Q4. Are both single slot and double slot cap options available on this model?

Yes — the APES_5X75 is available with either single slot 11.5mm ID or double slot 12.5mm ID fixing cap, like the APES_5X65. Identify your machine’s recess pin configuration (one or two pins) to select the correct cap.

Q5. What tip diameters are available for the APES_5X75?

Available in 4.7mm (3/16″) and 5mm/6mm tip diameters. Measure your existing sensor tip or machine well bore to confirm the correct OD.

Q6. Is NABL calibration available?

Yes — Aavad’s in-house NABL-accredited calibration laboratory issues traceable calibration certificates on request.

Q7. Does Aavad supply these bayonet RTD sensors across India?

Yes — PAN India from Ahmedabad with active deployments across Gujarat, Maharashtra, Delhi NCR, Haryana, Tamil Nadu, Karnataka, Telangana, AP, UP, Punjab, Kerala, Rajasthan, WB, and all other major Indian industrial states.

Buy Bayonet RTD Adjustable Length from India’s #1 Manufacturer

View the product page and download datasheet APES_5X75 or contact Aavad Instrument with your recess depth measurement to confirm the correct tip length.

📞 +91 90996 22823 | ✉ hrg@aavadinstrument.com | ISO 9001:2015 | NABL Accredited | Ahmedabad, Gujarat | PAN India Supply