UNITHERM ™ 6000 GUARDED HOT PLATE
THERMAL CONDUCTIVITY MEASURING SYSTEM

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Used to measure the thermal performance of insulations and other materials of high thermal resistance, the guarded hot plate is a primary measuring instrument that does not need to be calibrated with a known reference material. Due to the large sample size, the instrument is usable for testing even samples of inhomogeneous materials, including low density fibrous insulations, concrete, and composites. Depending on the temperature range, a variety of sample sizes can be accommodated, however, each instrument is only capable to test one fixed size specimen. These guarded hot plate instruments are designed in accordance with ASTM C177 and ISO 8302 specifications and can be used to test materials from -175°C to 550°C, in various range increments, depending on the model. Guarded hot plate instrument are used mostly for R & D testing where having the flexibility to meet many different applications and ultimate in accuracy is often more important than the speed of testing. All models are fully computer-controlled using current model PC's and Windows™ operating platform. Each unit is supplied with extensive operating and data reporting software. Here the user needs only to select the desired sample temperatures and the test proceeds unattended until completion. All testing parameters, such as equilibration criteria, heating rates, etc. are also user selectable within or outside of the applicable standards.

176;C to 550°C, in several ranges Absolute method, no reference needed ASTM C177 and ISO 8302 Fully automated operation Single or double sided construction

In most instances, single sided (one sample) designs are supplied, double sided (two sample) configurations are available as custom units

GUARDED HOT PLATE TEST METHOD

The material to be tested is placed on a flat plate heater assembly consisting of an electrically heated inner plate (main heater) surrounded by a guard heater. The guard heater is carefully controlled to maintain the same temperature on both sides of the gap separating the main and the guard heaters. This prevents lateral heat flow from the main heater and ensures that all heat energy flows in the direction of the sample. On the opposite side of the sample are additional flat plate heaters (the "cold" plate) that are controlled at a fixed temperature selected by the operator. For a given heat input to the main heater, the hot plate assembly rises in temperature until the system reaches equilibrium. The final hot plate temperature depends on the electrical power input, the thermal resistance of the sample, and the temperature of the cold plate. The average thermal conductivity, k, of the sample is determined from the Fourier heat flow equation:

where W is the electrical power input to the main heater, A is the main heater surface area, dT is the temperature difference across the sample, and d is the sample thickness. The thermal resistance of the sample is defined as:

During normal operation the heat sinks are cooled using city water. Since water temperatures can be as high as 30°C, the lowest attainable sample mean temperature is 50°C. To go below that a chiller/circulator is used. To reach cryogenic temperatures, liquid nitrogen is injected into the heat sink.
Features: Built-in thickness measurement, built-in compression stop, dead weight loading, gas tight enclosure for dry gas purge, dual guards (active), safety interlocks. Separate control cabinet.

To request a quote, please fill out our Request for Particulars form.
Specifications are subject to change without notice.