IEEE Std 442 pdf free download

IEEE Std 442 pdf free download.Thermal Resistivity Measurements of Soils and Backfill Materials.
4. Test equipment
Figure A. 1 and Figure B. 1 show diagrams of the system required to measure thermal resistivity in the laboratory or in the field. The equipment for testing differs primarily in the size of the probe and the portability requirements of the devices used in the field as shown in Annex A and Annex B.
4.1 Equipment required for field measurements
4.1.1 Field thermal probe
The field thermal probe is fabricated from a stainless steel tubing that can be made of various diameters and lengths. The tubing contains a heater element occupying the length of the seamless stainless steel tubing. A number of temperature sensors, electrically insulated from the heater element, and the probe body are shown in Annex A. Thermal probes of long lengths (more than 1 m) may contain multiple temperature sensors, positioned at intervals of 300 mm to 450 mm from the probe tip. with suitable means at the top of the probe for making electrical connections. In order to eliminate moisture infiltration in the probe and to reduce the initial thermal transient, the probe may be filled with an epoxy resin.
4.1.2 Power supply/power monitor
An adjustable, regulated electric power supply should be used in the constant current mode. The unit should be capable of providing a stable and constant power ranging from I W up to 250 W to allow flexibility to test with small lab probes and or large field probes. The field probes require higher power to heat the soil to the required temperatures and thus allow the determination of the soil’s thermal resistivity.
If such a power source is not available in the field, a portable generator or power inverter may be used to energize the heater in the probe. In such an application, accurate control can be exercised by using an ammeter and variable resistors to adjust the heater current. This configuration shall be able to adjust the currents between 0.1 A to 5 A and thus the heater power. Alternatively, power meter (digital or analog) may also be used to accurately measure the input power being applied to the heater in the probe.
5.2 Methods for laboratory measurements
5.2.1 Sample preparation and installation of laboratory probe
The laboratory thermal probe is used primarily to determine the effects of changes in density and moisture content on the resistivity of soil and backfill materials. It can be used for both undisturbed tube samples as well as reconstituted or re-moulded samples. If the soil is to be tested at the maximum density, ASTM D698, ASTM D1557, orASTM D2049 should be followed to determine the moisture content required at which the maximum density can be obtained. For most soils, the sample is mixed to the desired moisture content and then compacted to the desired density. Silty soils artificially moistened should be allowed to equilibrate for at least 12 h in an airtight container prior to sample preparation and testing. The soil should be compacted in 25 mm thick layers so that the density of the soil in the container remains relatively uniform. The sample should be placed in a rigid cylindrical container with a minimum inside diameter of 100 mm. The height of the container would vary depending on the length of the thermal probe used.
There are some sands that contain chemical deposits which form light bonds between sand particles as the sand dries. These bonds may lower the thermal resistivity of the sand due to the reduction in contact resistance between sand particles. Thus sand that is compacted at zero percent moisture could have a higher resistivity than sand that is compacted at a higher moisture content and then dried to zero percent moisture. Sand should be compacted to the condition in which it will be installed in the cable trench.
Care should be taken in inserting the thermal probe into the sample. If insertion of the probe is difficult, then a probe of slightly smaller diameter may be inserted into the soil to make a pilot hole.
IEEE Std 442 pdf download.