1. What is a Melt Pressure Sensor?

In core polymer manufacturing processes including extrusion, spinning and polymer synthesis, melt operating environments ranging from 200℃ to 400℃ have long been a major bottleneck for industrial pressure measurement. Featuring intense heat, viscous raw materials and corrosive media, such harsh conditions impose stringent standards for measuring equipment in terms of durability, precision and stability. Conventional pressure measuring instruments cannot withstand such extreme thermal environments. Prolonged operation commonly triggers data drift, declining measurement accuracy, equipment deterioration and drastically shortened service life. These defects lead to fluctuating process parameters, inconsistent product quality and frequent equipment breakdowns, which severely disrupt continuous and standardized polymer production.

Melt pressure sensors are core measurement & control devices custom-developed for severe melt operating conditions. They accurately detect subtle pressure variations inside melts and convert physical pressure signals into standardized electrical signals to deliver real-time, uninterrupted and precise pressure monitoring for production lines. For one thing, the sensors send instant alerts for overpressure risks to fully protect production equipment and prevent shutdowns, malfunctions and safety hazards arising from overloaded operation under high temperatures. For another, they maintain stable process parameters and consistent production performance, greatly cutting defective and rework rates caused by inaccurate, erratic pressure readings in hot environments. This facilitates efficient, stable, low-consumption and high-quality operation of smart polymer production lines, making the sensors essential core measuring and control components for melt manufacturing processes.

To tackle the prevalent industry challenge of pressure measurement at high temperatures, GRAEFF has devoted years to sensor technology development. Supported by three proprietary core technologies — NTX multi-alloy filling technology, AI intelligent zero thermal drift technology and NFM medium-free transmission technology — we deliver targeted solutions to measurement challenges under high-temperature conditions. Furthermore, our comprehensive G-series product portfolio fits a wide range of application scenarios, such as general mass production, high-end clean production, explosion-proof chemical processing and large pipeline flange mounting, covering nearly all melt pressure measurement demands across industries.

2.Working Principle of Melt Pressure Sensors

Many think melt sensor technology works in a complicated way, but its core principle is easy to understand. During production, pressure from melt acts directly on the front sensing diaphragm of the sensor, causing tiny deformation proportional to the pressure.

Such deformation changes the resistance of internal strain gauges. The built-in high-precision circuit captures resistance variations in real time, calculates the actual pressure via Wheatstone bridge, and outputs standard industrial signals like 4–20mA, 0–10V and mV/V to realize visual, intelligent and precise melt pressure measurement and control

Working Logic of the Wheatstone Bridge

The bridge forms a closed loop with four precision strain resistors: one pressure-sensitive resistor and three fixed reference resistors. The loop remains current-balanced under no pressure. Once melt pressure deforms the diaphragm and alters resistance values, the bridge balance breaks to output an accurate differential voltage, which is then amplified and converted by circuits to obtain precise melt pressure data.

3.Three Core Technologies of GRAEFF Melt Pressure Sensors

1. NTX Multi-Alloy Filling Technology

Mercury-free liquid multi-alloy serves as the pressure transmission medium to accurately transfer actual melt pressure. Its low thermal expansion property avoids common drawbacks of traditional silicone oil such as high-temperature volatilization and carbonization, as well as heavy metal pollution caused by mercury medium.

With this technology, the device works stably under long-term working conditions up to 300℃ with reliable signal output, delivering a measurement accuracy of ±0.5% FSO. Equipped with a dedicated intelligent compensation circuit to further restrain temperature drift, it meets precise melt measurement and control requirements in extrusion, rubber, aramid and other industries for long-term continuous production.

2. AI Intelligent Zero-Temperature-Drift Technology

Equipped with built-in temperature sensors and an embedded intelligent computing chip, it adopts a full-range calibration database covering multiple temperatures and pressure points as well as self-developed AI decoupling algorithm to identify the coupled zero and sensitivity temperature drift caused by core strain resistors, NTX multi-alloy filling medium and metal diaphragms, and dynamically correct output signals automatically.

Unlike traditional single hardware static compensation that only offsets measurement deviation within a narrow range, this technology dynamically suppresses temperature drift across a wide temperature range. Combined with heat insulation and dissipation structures, it maintains stable measurement accuracy of ±0.5% FSO under long-term working conditions up to 400℃, reducing frequent on-site zero calibration. It is ideal for high-precision continuous melt measurement and control in extrusion, aramid and lithium battery industries.

3. NFM Medium-Free Conduction Technology

Abandoning filling media like silicone oil and NTX liquid alloy, the integrated metal elastic force-transmitting structure enables direct pressure transfer, fundamentally eliminating hidden troubles such as medium leakage, high-temperature carbonization and thermal expansion drift.

Melt pressure is rigidly transmitted through the Hastelloy diaphragm directly to the Wheatstone bridge of the sensing core, featuring no medium loss and faster pressure response. It operates stably for long-term use at up to 400℃ with a measurement accuracy of ±0.5% FSO. Free from medium contamination, it suits ultra-clean melt production in food, pharmaceutical, aramid and lithium battery industries, greatly lowering later maintenance and scrapping risks caused by leakage.

4.G Series Melt Sensors / Transmitters

GEMP Series Melt Pressure Sensors / Transmitters

Adopting NFM dielectric-free technology, this series delivers stable and reliable performance. It supports various mounting thread specifications and complete output signals complying with universal industrial standards. With an IP65 protection rating, it achieves accurate melt pressure measurement under harsh working conditions, offering reliable measurement solutions for food, pharmaceutical and other industries.

GINS Series Melt Pressure Sensors / Transmitters

The main body is made of stainless steel, while other components are fabricated via special processes and have passed high-strength tests. The diaphragm is protected by a special coating, shielding it from substances with high viscosity and friction. This series features a long service life, precise measurement performance, minimal temperature drift and excellent operational stability.

GMP Series Melt Pressure Sensors / Transmitters

This precision measuring device adopts high-performance core components and anti-interference analog circuits. Calibrated at 350°C, it delivers superior measurement accuracy.

GHP Series Melt Pressure Sensors / Transmitters

This precision measuring device adopts high-performance core components and anti-interference analog circuits. Calibrated at 350°C, it delivers superior measurement accuracy.

GCM Series Melt Pressure Sensors / Transmitters

Constructed from stainless steel, its components are produced by special processes and have passed high-strength tests. A special titanium compound coating shields the diaphragm against high-viscosity and abrasive substances. This series offers long service life, precise measurement, low temperature drift and stable performance. Adopting eco-friendly NTX alloy filling technology, it is applicable to food, pharmaceutical and other industries.

GM Series Melt Pressure Sensors / Transmitters

The main body is made of stainless steel, with other components fabricated via special processes and tested for high strength. A special titanium compound coating protects the diaphragm from high-viscosity and abrasive materials. This series features long service life, precise measurement, low temperature drift and stable performance. Equipped with eco-friendly NTX alloy filling technology, it can be applied in food, pharmaceutical and other industries.

GMX Series Melt Pressure Transmitters

The main body is made of stainless steel, and other components are manufactured through special processes and pass high-strength tests. A special titanium compound coating protects the diaphragm from high-viscosity and abrasive substances. This series boasts long service life, precise measurement, food-grade transmission medium, low temperature drift and stable performance. Adopting eco-friendly NTX alloy filling technology, it is suitable for food, pharmaceutical and other industries.

GMC Series Melt Pressure Sensors / Transmitters

It offers optional accuracy of ±0.25% FSO and ±0.5% FSO with 80% internal calibration for excellent stability and repeatability. Multiple output signals including 3.33mV/V, 0–5V, 0–10V and 4–20mA as well as various electrical connections are available. Designed with special threaded mounting, it features easy installation, high reliability, long service life, precise measurement and low temperature drift. Its unique exposed structure meets the requirements of special application environments.

GMR Series Melt Pressure Sensors / Transmitters

It adopts high-performance TI digital chips. The circuit complies with SIL 2 and PLC safety standards. Relay outputs are used for range limit control to secure extrusion equipment and production lines, effectively preventing equipment damage caused by overpressure and potential personal safety accidents. It is suitable for extrusion equipment and production lines requiring precise process control, widely used in refrigeration, chemical, environmental protection and other industries.

GAIM Series AI Intelligent (Zero Temperature Drift) Melt Pressure Sensors / Transmitters

Equipped with temperature compensation technology, the product is calibrated for zero drift at 350°C. Near-zero temperature drift is achieved when the pressure probe works under high temperatures, enabling GAIM series sensors to deliver more accurate and stable measurement.

GAIMX Series AI Intelligent (Zero Temperature Drift) Melt Pressure Transmitters

It adopts temperature compensation technology to realize zero drift calibration at 350°C, achieving nearly zero temperature drift when the pressure probe works under high temperatures. Integrated with an intelligent 4~20mA+HART protocol circuit, GAIMX series transmitters feature higher measurement accuracy and stability.

GPX Series Melt Pressure Sensors / Transmitters

The main body is stainless steel, and other components are manufactured via special processes and have passed high-strength tests. A special titanium compound coating protects the diaphragm from high-viscosity and abrasive substances. This series features long service life, precise measurement, food-grade transmission medium, low temperature drift and stable performance. With eco-friendly NTX alloy filling technology, it can be applied to food and pharmaceutical industries.

GMPG Series Melt Mechanical Pressure Gauges

This pressure measuring product features a 4-digit LED display, no indication error and dual-relay control. It can operate normally at up to 400°C, is installed via standard thread connection, and delivers high stability and long service life.

GMG Series Intelligent Digital Melt Pressure Gauges

This pressure measuring device is designed for high-temperature environments. It is equipped with a 4-digit LED display, free of indication errors and supports two-channel relay control. Capable of stable operation up to 400°C, it adopts standard threaded connection for installation, featuring high stability and long service life.

GIS Series Potentiometer Zero-adjustment Signal Converters

It realizes sensor signal isolation, amplification and standard conversion with strong anti-interference performance. Compatible with analog and digital outputs, it can be easily connected to industrial control systems. Suitable for melt and general industrial process measurement, it is widely applied in automatic measurement and control of plastics, rubber, chemical fiber, petrochemical and other industries to ensure precise and reliable detection.

5.Application Fields

1.Plastic Industry

Main Applications

Suitable for various plastic molding processes including extrusion, injection molding, blow molding, casting and calendering. It can be installed on key positions such as screen changers, molds, nozzles and cavities to monitor real-time melt pressure and realize closed-loop control of production processes.

Functions

It stabilizes plasticizing quality and extrusion flow to prevent equipment damage from overpressure. Meanwhile, it optimizes filling and holding pressure parameters, reduces defects like sink marks and flash, stabilizes dimensional accuracy and improves the yield rate of finished products.

2. Chemical Fiber Industry

Main Applications

Mainly used in melt spinning production lines. Installed on spinning beams and before & after metering pumps, it monitors the melt pressure of polymers such as polyester, nylon and polypropylene, providing data support for stable fiber forming.

Functions

Precise pressure and flow control matches the spinning conveying rhythm to ensure uniform fiber fineness. It reduces frequent defects including filament breakage, fuzzy yarn and uneven thickness, stabilizes spinning efficiency and lowers reject rates.

3. Chemical Industry

Main Applications

It is applicable to polymer synthesis reactors, high-temperature molten material conveying pipelines and other equipment for real-time pressure monitoring and process control of thermal medium working conditions.

Functions

It monitors melt pressure throughout the whole process to ensure stable chemical reactions within safe ranges, stabilizes the conveying efficiency of high-temperature materials, avoids hidden dangers caused by overpressure, and guarantees safe, orderly and controllable continuous chemical production.

4. Rubber Industry

Main Applications

It is applied to core processes of rubber extrusion and calendering, monitoring the melt pressure of mixed rubber in extruders and calender rolls to provide measurement and control support for mass production of various rubber products.

Functions

It precisely regulates melt pressure and fluidity, stabilizes extrusion dimensions and calendering thickness, reduces molding defects, and effectively improves the compactness and molding consistency of rubber products.

5. Food Industry

Main Applications

It can be used in food packaging as well as high and low-temperature molten food production lines for chocolate, candy, grease and other products. It monitors pressure throughout material melting and conveying, complying with hygienic standards for food-grade production.

Functions

By stabilizing melt conveying pressure and production processes, it ensures consistent finished food quality and reduces batch-to-batch differences, enabling clean, standardized, continuous and stable food production.

6. Pharmaceutical Industry

Main Applications

It is suitable for pharmaceutical hot melt extrusion processes, widely adopted in the production of high-end drugs such as sustained-release preparations, to monitor the melt pressure of mixed medicinal powder and polymers.

Functions

Accurate and stable extrusion pressure ensures uniform material mixing and consistent production processes, improves drug forming performance and the uniformity of drug efficacy, and meets the high cleanliness and high-precision production requirements of the pharmaceutical industry.

7. Metallurgical Industry

Main Applications

It is suitable for metallurgical equipment including melting furnaces, holding furnaces and die-casting machines, covering the whole working process of metal smelting and die casting.

Functions

It enables precise measurement under harsh high-temperature conditions, stabilizes die-casting injection processes and reduces forming defects, ensuring uniform dimensions and stable quality of die castings.

6.Quick Selection Guide

1.Model Selection Based on Medium Cleanliness Grade and Material Requirements

For mass production of general rubber and plastics, conventional food processing, pharmaceutical manufacturing, lithium battery separators, aramid fibers, optical films and other common working conditions, series products equipped with NTX multi-alloy filling technology (GINS, GMP, GHP, GCM, GMC, etc.) are applicable. Their filling medium complies with food-grade standards and fits most conventional production scenarios.

For high-cleanliness production conditions in the food and pharmaceutical industries where direct contact between the medium and raw materials is prohibited, the GEMP series adopting NFM medium-free conduction technology is the preferred choice, fundamentally eliminating risks of medium leakage and cross-contamination of materials.

For flammable and explosive chemical workshops, GMX and GAIMX explosion-proof series with official explosion-proof certifications are recommended. Combined with NTX eco-friendly alloy filling technology and AI intelligent temperature compensation technology, they can meet the application requirements of high-risk explosion-proof production environments.

2.Model Selection Based on Medium Temperature and Accuracy Requirements

Conventional working conditions below 300°C: All NTX medium-filled sensor models are available, widely applied in most medium and low-temperature production scenarios such as rubber & plastics, food, pharmaceuticals and chemical fibers with stable performance and strong versatility.

High-temperature and high-cleanliness working conditions ranging from 300°C to 400°C: The GEMP medium-free series is preferred. Adopting the NFM medium-free conduction structure, it can withstand long-term working temperature up to 400°C, fundamentally avoiding medium carbonization, leakage and contamination, suitable for various high-temperature clean production processes.

For production scenarios demanding high measurement stability and precision and sensitive to temperature fluctuations, the GAIM and GAIMX intelligent series equipped with AI intelligent zero-temperature-drift technology are highly recommended. With professional temperature compensation technology for zero drift calibration under 350°C high temperature, the probe achieves nearly zero temperature drift during high-temperature operation, greatly improving the overall measurement accuracy and stability of the equipment.

3.Model Selection Based on Installation Structure, Special Working Conditions and Explosion-proof Requirements

General installation for extruder dies: The 1/2" UNF standard thread series is recommended, with optional thread specifications including M18, M14 and others.

Large-volume reaction kettles and high-flow melt conveying pipelines: GM and GMX flange-mounted series are adopted.

Limited installation space and special working conditions requiring exposed structure: The GMC series with dedicated exposed design is preferred.

Explosion-proof workshops: GMX and GAIMX series with explosion-proof certifications are recommended. GMX is suitable for flange-mounted large-caliber explosion-proof scenarios, while GAIMX applies to high-precision threaded explosion-proof occasions.