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Minimizing Drift in Electrical Conductivity Measurements in High Temperature Environments using the EM-38

USDA-ARS, George E. Brown, Jr. Salinity Lab., 450 W. Big Springs Road, Riverside, CA 92507

View larger version (34K): [in a new window]   Fig. 1. (A) Data from field mapping where the same row was run in the morning and again later in the day showing responses that follow each other with an offset. (B) A similar data set from another field site run in the morning and again later in the day, where the response jumps at point 730.

View larger version (27K): [in a new window]   Fig. 2. Schematic diagram of the EM-38, which is 1 m in length. Tx is the transmitting coil and Rx is the receiving coil. Locations CP and Rx are where the temperature sensors were placed.

View larger version (31K): [in a new window]   Fig. 3. (A) Temperature response for control panel (CP) and receiving coils (Rx) of the EM-38 with the central 50 cm of the instrument wrapped in an electric blanket and warmed. (B) The soil bulk electrical conductivity (ECa) response, which reduces as the instrument panel is warmed.

View larger version (27K): [in a new window]   Fig. 4. (A) Temperature response for control panel (CP) and receiving coil (Rx) of the EM-38 with the whole instrument wrapped in an electric blanket and warmed. (B) The soil bulk electrical conductivity (ECa) response, which demonstrates the temperature compensation up to 140 min and then an unpredictable response as temperature increased above 40°C.

View larger version (51K): [in a new window]   Fig. 5. (A) Panel temperatures (control panel [CP], Fig. 2) for five days. (B) Temperature difference between CP and receiving coil (Rx) for the five days. (C) The instrument responses with increasingly hot panel temperatures. (D) Electromagnetic response with the instrument shaded.

View larger version (36K): [in a new window]   Fig. 6. (A) Temperature of the EM-38 corresponding to the locations under the handle (receiving coil [Rx], Fig. 2) and on the panel (control panel [CP], Fig. 2) of the instrument. (B) The soil bulk density of electrical conductivity (ECa) response on the asphalt in the vertical orientation without being moved, Points A-E are described in the text.