IEEE 442-2017 pdf free download – IEEE Guide for Thermal Resistivity Measurements of Soils and Backfill Materials.
4. Test equipment Figure A.I and Figure B. I 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, clectrically 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 flled with an epoxy resin.
4.1.2 Power supply/power monitor An adjustable, regulated clectric power supply should be used in the constant current mode. The unit should be capable of providing a stable and constant power ranging from 1 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 Ato 5A 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.
4.1.3 Temperature monitor A multipoint portable digital instrument designed to measure temperatures with a resolution of better than 0.1 °C is preferred for field use. Manual balance potentiometers with reference junctions have also been used succssfully.
4.2 Equipment required for laboratory measurements
4.2.1 Laboratory thermal probe Laboratory measurements use a small stainless steel probe with a length to diameter ratio of 50:1. The internal parts ofthe probe include a heater element and a temperature sensor that are both electrically insulated from each other and fom the stainless stcel probe body. Detailed diagrams are depicted in Figure B.I and Figure B.2 of Annex B.
4.2.2 Power supply/power monitor An adjustable regulated de power supply is required with the capability of providing at least 20 W. Alternatively, power meter (digital or analog) of up to 20 W can be used in place of power supply for the power input to the thermal probe.
4.2.3 Temperature monitor A multipoint portable digital instrument designed to measure temperatures with a resolution ofbetter than0.1。C is preferred for lab use. Manual balance potentiometers with reference junctions have also been used succssfully.
5. Test methods
5.1 Methods for field measurements
5.1.1 Installation of field probe The thermal probe with multiple temperature sensors should be carefully inserted in the earth. The probe should be inserted such that the middle temperature sensor is located at the depth that the cable is to be installed. Resistivities could then be determined at the cable depth and 300 mm above and bclow that depth. If, due to soil conditions, insertion of the probe is dificult, a pilot hole should first be made. Under no conditions should the thermal probe be hammered or inserted with excessive force into the soil. When a pilot hole is needed, a pilot rod of slightly smaller diameter than the thermal probe should be driven into the soil using a slide hammer and guide (Annex C), or another appropriate device. Similar means should be used to remove the pilot rod. If insertion of the thermal probe is difficult, because of unusual soil conditions, the pilot rod should be reinserted and removed again. This process can be repeated until the hole is just enlarged enough to accommodate the probe to minimize the contact resistance at the probe/soil interface. If the soil is extremely rocky, an ectric drill may be used to facilitat producing a pilot hole. In any event, if the ambient termperature is raised as a result of this process, enough time should be allowed for the ambient temperature to return and stabilize at the initial condition. This may be several minutes to over an hour.IEEE 442 pdf download.