IEEE 442-2017 pdf download

IEEE 442-2017 pdf download.IEEE Guide for Thermal Resistivity Measurements of Soils and Backfill Materials.
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
successfully.
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 of5O: 1. The internal parts ofthe probe include a heater element and a temperature sensor that are both electrically insulated from each other and from the stainless steel probe body. I)etailed diagrams are depicted in Figure B. 1 and Figure 11.2 of Annex B.
4.2.2 Power supplylpower monitor
An adjustable regulated dc power supply is required with the capability of providing at least 20W. 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 theniial probe.
4.2.3 Temperature monitor
A multipoint portable digital instrument designed to measure temperatures with a resolution ofbetter than 0.1 °C
is preferred for lab use. Manual balance potentiometers with refcrcnccjunctions have also been used successfully.
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 below that dcpth. If, due to soil conditions, insertion of the probe is difficult, a pilot hole should first he made. Under no conditions should the thermal probe he 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 electric drill may be used to facilitate producing a pilot hole. In any event, if the ambient temperature 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.
5.1.2 Test procedure for field probe
After insertion has been completed, the following procedure should be performed:
a) Make power and temperature monitoring connections.
b) Conduct a verification test of the thermal probe prior to field testing by measuring a known standard for every project and compare with the calibration certificate.
c) Allow 10 mm to 15 mm for the probe to reach thermal equilibrium with the surrounding earth while monitoring the temperature at 2 mm intervals. This time will depend on the difference between the air temperature and earth temperature (natural and induced by the process used for installation).
d) Select a power level that will give at least 3 °C to 4 °C temperature rise over approximately one logarithmic cycle of time to allow for easy interpretation of the measured data. Depending on the size, heat input between 30 W/m and 50 W/m is usually applied to the field thennal probe. The power selected depends on the resistivity of the soil and will have to be based on experience for a given type of soil. If the soil has a very low resistivity, then a high heat input is required to produce an acceptable temperature change. Ifthe soil has a very high resistivity, then a low heat input is required to keep from overheating the probe that can also induce moisture migration. If the probe temperature reaches 50 °C at any time, the test should be terminated immediately, and a lower heat flux should be applied to the probe at the next location.
e) Switch on the power to the probe heater.
f) Regulate the constant current power supply.
g) Record temperatures of each temperature sensor in turn at 30 s intervals for the first 5 mm to establish that the probe is not overheated. The temperature should not exceed 10 °C above ambient soil temperature, during the first 5 miii under normal conditions
h) Continue recording temperatures in turn at 1 mm intervals for 30 mm to 40 mm or until the logarithmic temperature rise becomes linear. At the end of this time, switch off the power to the probe heater.