These web pages may be helpful in making these calculations: http://onlineconversion.com/length_all.htm (opens new window), http://www.csgnetwork.com/sntodeccalc.html (opens new window). C1 & C2 are the outer probes and P1 & P2 are the inner probes. The RM Series Test Units also have a button which can be pressed to auto-range to determine the best choice of input current for the material being measured. For sixty seconds, a voltage is applied and the resistance is measured. When left will little room or poor conditions in which to conduct a proper soil resistivity test, one should use the closest available open field with as similar geological soil conditions as possible. COPYRIGHT © 2020 FOUR-POINT-PROBES. 19 What is the expected life of a Jandel Four Point Probe Head? These are the probes that inject current into the earth. A. 21 Wikipedia article regarding the Hall Effect, 22 Wikipedia article regarding the Van der Pauw method, 23 NIST web page regarding the theory and implementation of the Hall Effect Measurement technique, HOME | PRODUCTS | TECH INFO | FAQ | ABOUT | CONTACT. The formula is 2 x pi x s x V/I where s is the spacing between each of the needles in cm. The new RM Series Test Units can read out directly on the screen in ohm-cm (volume resistivity) if one inputs the sample thickness or if one indicates that a bulk material is being measured, in addition to reading out in either sheet resistance expressed in ohms-per-square or in millivolts. In this situation we can say that: bulk resistivity = sheet resistance x thickness in cm. Here are just a few of the mistakes you will learn about: This article discusses ground potential rise studies and soil resistivity testing for high voltage transmission towers and is applicable for any ground potential rise analysis. Note: we only store your data so that we can contact you with relevant information and we never share personal data with 3rd parties. To accurately calculate how those conductors will perform at these depths shallow soil readings must be taken. The inner two probes are the Potential probes, P1 and P2. These are the probes that take the actual soil resistance measurement. Shallow depth readings of 6-inches, 1-foot, 1.5-feet, 2-feet and 2.5-feet are important for grounding design, because grounding conductors are typically buried at 1.5 to 2.5-feet below the surface of the earth. In other words, at what point is a sample so thick that it is no longer valid to measure it as a thin film? It is a question of what you consider to be okay. Less than 40% of the tip spacing and the measurements need no correction. From the graph at http://www.fourpointprobes.com/page14.pdf it would appear that if you measure bulk on a 550 micron wafer with a 1.591mm probe head then t/s = 0.34 and a correction of 0.25 would need to be applied. Soil resistivity testing is the single most critical factor in electrical grounding design. Join our community and get complete access to our free library of Whitepapers, Many materials that are thick or relatively large such as silicon ingots (as opposed to a thin film or layer), can be measured using a four point probe to determine the volume resistivity. Continue moving the three probes (C2, P1 & P2) away from C1 at equal intervals to approximate the depth of the soil to be measured. When compared to the HM21, the RM Series Test Units have a greater measurement range on both ends of the scale and it they auto-range, whereas the HM21 does not auto-range. ], Some information about selecting the best choice of input current when using four point probe electronics that do not auto-range can be found here: http://www.fourpointprobes.com/reversing_current.pdf. At this point, a known current is applied across probes C1 & C2, while the resulting voltage is measured across P1 & P2. The term ohms-cm (“ohms centimeter”) refers to the measurement of the “volume” resistivity (also known as “bulk” resistivity) of a semiconductive material. Four-Point-Probes is a division of Bridge Technology. Data:Surface and Volume resistivity are calculated. Care should always be given when selecting a soil resistance meter, as the electronics involved in signal filtering are highly specialized. This crops up regularly, and it is hard to answer – let me give you an example to show the problem. Depending upon the equipment’s maximum voltage, Low-Frequency meters can take readings with extremely large probe spacings and often many thousands of feet in distance.