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What is REP

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Charlie Vuong edited this page Oct 12, 2026 · 26 revisions

A REP (retraction-extrusion pulse) is the measurement RheoBoard runs.

The board draws a sample into a tube, then pushes it back out. One pump pulls. The valve switches. The other pump pushes. A pressure sensor on the air line records the trace. The shape of that trace is a short record of how the material flows.

Equation

The air in the line follows (PV = nRT). (P) is the pressure the sensor reads, (V) is volume, (n) is the amount of gas, (R) is the gas constant, and (T) is temperature.

Sensing method. A pneumatic actuator retracts and extrudes. An air pressure sensor is on the line. The diagram marks PV = nRT.

How a REP works. The diagram marks (PV = nRT).

How a REP looks

A REP measures how a material responds to a brief pull and push. The pressure trace follows three phases: retraction, extrusion, and stabilization.

Pressure versus time from 0 to 1200 ms. Retraction, extrusion, and stabilization are shaded. Peak vacuum and peak pressure are marked. Red dots are pressure-and-time features. Blue bars are period features. Schematic, not measured.

Pressure trace from 0 to 1200 ms. Peak vacuum in retraction, peak pressure in extrusion, then stabilization. Schematic, not measured.

Setup

RheoBoard uses two pumps and a switching valve to draw a sample into a tube and push it back out. A sensor on the air line records the pressure throughout the cycle.

Bench with the probe, actuator, and sensor. The airtube probe retracts and extrudes a sample. A 1–2 second routine captures air pressure.

Bench with the probe, actuator, and sensor.

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