Melt Pressure Transducers

Home › Products › Pressure Instruments › Melt Pressure Transducers

Melt pressure is the one process variable an extrusion line cannot run blind on. Pressure ahead of the breaker plate tells you when the screens are loading up. Pressure at the die inlet tracks product dimensions. Pressure at a melt pump inlet and outlet proves the pump is fed and not deadheaded. The SI-PT series measures all of these points with the diaphragm wetted by the melt itself, so there is no impulse line to freeze off with solidified polymer.

If your application is hot fluid in a pipe rather than melt in a barrel, look at our high-temperature pressure transmitters instead; they carry the cooling structure for that job.

Selecting the model

Eight SI-PT models cover this job. Match the line’s needs to a starting model here, then confirm the range, accuracy and diaphragm rating in the specification table below.

Your situation	Start with
General extrusion, standard accuracy, best value	SI-PT111
A 4–20 mA or voltage signal straight into the PLC, with no separate amplifier	SI-PT112
Pressure and melt temperature from the same point	SI-PT127 (or SI-PT131)
Replacing a Dynisco, GEFRAN or RKC sensor	SI-PT124 (pressure) or SI-PT131 (pressure + temperature)
Tight or curved mounting, or heavy vibration	SI-PT123 (flexible capillary)
A flange connection instead of a threaded port	SI-PT2616
A hazardous or explosive area, or a HART signal	SI-PT292
The tightest accuracy, ±0.25% FS	SI-PT112, PT123, PT124 or PT292

Models at a glance

Model	Type	Range	Accuracy	Diaphragm	Output	Notes
SI-PT111	Rigid stem	0–5 to 0–100 MPa	±0.5 / 1.0% FS	300 °C	0–5 V, 0–10 V, 4–20 mA	Workhorse; wear-resistant coating option
SI-PT112	Rigid stem, amplified	0–5 to 0–200 MPa	±0.25 / 0.5% FS	Consult factory	0–5 V, 0–10 V, 4–20 mA or mV/V	Zero and span adjustable; feeds PLC direct
SI-PT123	Flexible capillary	0–3.5 to 0–150 MPa	±0.25 / 0.5% FS	350 °C (400 °C max)	2 / 3.33 mV/V	15-5PH coated diaphragm; built-in temperature sensor
SI-PT124	Rigid stem	0–5 to 0–200 MPa	±0.25 / 0.5% FS	450 °C	1.5 / 2.0 / 3.3 mV/V	Drop-in for Dynisco, GEFRAN, RKC
SI-PT127	Rigid stem, pressure + temperature	0–5 to 0–200 MPa	0.5 / 1% FS	450 °C	1.5 / 2 / 3.33 mV/V	J, K, E thermocouple or PT100 in one body
SI-PT131	Rigid stem, pressure + temperature	0–5 to 0–200 MPa	±0.5 / 1.0% FS	450 °C	1.5 / 2.0 / 3.3 mV/V	7-core connector; Dynisco, GEFRAN, RKC interchange
SI-PT2616	Flange mount	0–5 to 0–200 MPa	≤±0.5% FS	300 °C	1.5 / 2.0 / 3.3 mV/V	Flange sized to order
SI-PT292	Hazardous area	0–500 to 0–30,000 psi	Better than ±0.25%	Consult factory	4–20 mA loop powered + HART	Class I Div 1 Groups A–D; ATEX II 1 G; EEx ia IIC

Technical specifications

Parameter	Specification
Pressure ranges	0–3.5 MPa to 0–200 MPa by model; SI-PT292 spans 0–500 to 0–30,000 psi
Accuracy	±0.25% FS to ±1.0% FS, model and range dependent
Power supply	10 VDC (6–12 VDC) sensor versions; 24 VDC (12–36 VDC) amplified PT112; PT292 is 4–20 mA loop powered
Output signal	1.5 / 2.0 / 3.33 mV/V; 0–5 V; 0–10 V; 4–20 mA; HART digital on PT292
Internal calibration	80% FSO shunt calibration, ±1%
Diaphragm temperature	300 °C (PT111, PT2616); 350 °C, 400 °C max (PT123); 450 °C (PT124, PT127, PT131)
Temperature drift	≤0.30 MPa per 100 °C (PT111, PT124)
Overpressure	1.5 × full scale
Diaphragm material	Stainless steel; 15-5PH with protective coating on PT123; optional anti-corrosion, wear-resistant coating extends life 3 to 5 times in abrasive filled melts
Process connection	1/2"-20UNF, M14 × 1.5, M18 × 1.5, M22 × 1.5, G3/4; flange to order on PT2616
Electrical connection	5-pin or 6-pin connectors; 7-core on PT131; wire leads on PT292
Hazardous area (PT292)	Class I, Division 1, Groups A, B, C, D; ATEX II 1 G; EEx ia IIC zones 0 and 1

Specifications apply at room temperature and rated supply unless stated. Diaphragm ratings are wetted-end limits, not electronics ratings. Confirm the exact figure for your model and range on the order sheet.

Mounting position

The measuring principle is direct. Melt pressure acts on the diaphragm, the diaphragm deflects a few microns, and that deflection changes the resistance of the strain gage bridge behind it. The electronics convert the resistance change into a standard signal. No fill ports, no impulse tubing, nothing for polymer to solidify inside.

Put the sensors where they earn their keep. One sensor upstream of the breaker plate watches the screen pack: as the screens load up with contamination, pressure climbs, and a rising trend tells the operator to change screens before the screw starts working against a wall. A pair across a melt pump proves the pump is fed at the inlet and not blocked at the outlet. A sensor at the die inlet holds the pressure that sets product dimensions, which is where scrap rates are won or lost on sheet and pipe lines.

From the case file: an engine builder in Southeast Asia needed pressure measurement against hot combustion gas in a diesel test rig at 0–250 bar with 0–5 V and 0–10 V outputs at roughly 1% accuracy. The same construction logic applies in both jobs: keep the diaphragm in the hot medium and the electronics out of it.

Replacing Dynisco, GEFRAN and RKC sensors

SI-PT124 and SI-PT131 are built to interchange with the common imported melt sensors: same 1/2"-20UNF mounting thread, same mV/V output levels, same 80% FSO internal calibration convention. Swapping one out is a like-for-like exchange, not a rewiring project. Match four things and the swap works: the mounting thread, the pressure range, the output signal, and the connector pinout. Send us the model code printed on the label of your existing sensor and we will match it line by line.

Ordering information

An SI-PT sensor is configured per application, not pulled off a shelf. Pick the range so your working pressure sits at 60 to 80% of full scale; overload protection is 1.5 × full scale, and a sensor sized this way rides drift and spikes without giving up resolution. Then choose the diaphragm rating for the melt temperature at the mounting port, not the barrel setpoint two zones away.

Ordering example: SI-PT124, range 0–35 MPa, 1/2"-20UNF thread, 3.33 mV/V output, 450 °C diaphragm, 5-pin connector, as a drop-in for an existing Dynisco port on a 90 mm extruder. Working screen-pack pressure of 22 MPa sits at 63% of full scale.

Applications

Related products

FAQ

What is a melt pressure transducer?

A pressure transducer built to measure molten-polymer (melt) pressure on an extrusion or injection line. It mounts flush at the barrel or die, withstands the high process temperature, and outputs 4–20 mA. The SI-PT series has several models for the position and range on the line.

What are the three types of pressure transducers?

By reference: gauge (versus atmosphere), absolute (versus vacuum), and differential (between two points). A melt pressure transducer is a gauge type, reading the melt pressure against atmosphere.

What is the purpose of a pressure transducer?

To convert pressure into a standard electrical signal the control system can read. On an extrusion line the melt transducer protects the process: it monitors die pressure for product quality and trips before an overpressure damages the screen pack or tooling.

How do you know if a melt pressure transducer is bad?

It drifts, sticks at a value, or loses output; on a melt line a coated or damaged diaphragm shows as a slow or noisy reading. Zero it at no load and compare against a known reference, and replace it if it will not zero or track.

Request a quote

Tell us the pressure range, the melt temperature at the port, the thread and the output signal. We respond with a configured model code, lead time and price, usually within one working day.